NUTRIENT INPUTS FROM TREES VIA THROUGHFALL, STEMFLOW AND

LITTERFACL IN AN INTERCROPPING SYSTEM

A Thesis

Presented to

The Faculty of Graduate Studies

of

The University of Guelph

by

PlNG ZHANG

In partial fulfilment of requirements

for the degree of

Master of Science

July, 1999

O Ping Zhang. 1999

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NUTRIENT INPUTS FROM TREES VIA THROUGHFALL, STEMFLOW AND LllTERFALL IN AN INTERCROPPING SYSTEM

Ping Zhang University of Guelph, 1999.

Advisor: A- M- Gordon

The purpose of this study was to determine the amount of nutnent input frorn

tree rows to adjacent crops in an agroforestry intercropping system and to evaluate

the effects of those inputs on crop growth- Concentrations of N, P, K, Ca, and Mg

were rneasured in open rainfall and in throughfall, stemflow and Iitterfall from

various tree species. Average annual nutrient inputs (kg-ha-') for total-N, NO,-N.

NH,-N, Pl K. Ca and Mg were 7.49,1.04, 1.11, 2.44. 8.53, 19.09 and 4.76,

respectively. LitterfaIl frorn the plantation canopy was the major contributor of N

(90.5% of al1 nitrogen inputs), whereas throughfall contributed the most K (62.7%

of al1 potassium inputs) and stemflow accounted for a very small proportion of the

nutrients but contributed the most P (50.3% of al1 phosphorus inputs). Wheat growth

response showed that the average wheat yield within 1 m of the tree row was 1-6

times the yield at a distance of 6m from the tree row.

ACKNOWLEDGEMENTS

I would like to thank the members of my advisory cornmittee. Dr. Paul

Voroney, Dr. Victor R. Timrner and especially my advisor. Dr. Andrew M. Gordon,

for this opportunity to pursue graduate research. Thank you for ail of the insightful

discussions, guidance, advice, encouragement and continued support. 1 would also

like to thank the Ontario Ministry of Agriculture and Rural Affairs for providing

financial support-

I would like to acknowledge the efforts of sevzral my dear friends - Dr.

Naresh Thevathasan for helping me settle down and for technical advice, especially

regarding laboratory equipment and field protocols. Ms. Elaine Mallory for

encouragement, friendship and proof-reading and Mr. Jamie Simpson for statistical

assistance.

To al1 of my friends, CO-workers and members of the Agroforestry Research

Group (especially Rick Gray, Nancy Luckai, Gordon Price, Rob McCart. Allison

Back, Kelly Bowen, Glen Wilson, Maren Oelbermann, Shelly Hunt, Heather

Middleton, Sandra Cook and lan Short), I extend my overall appreciation and

gratitude. Thank you for giving me strength and courage, for always being there,

for understanding and supporting me and for providing continual help.

I also wish to express gratitude to my parents for their continued love, for

their encouragement of me to work hard to achieve my goals, as well as for

providing unconditional help when I encountered difficulties during my study.

Finally, to al1 who helped me improve my English during the course of my

study - thanks!

All of you have helped make rny dream a reality!

TABLE OF CONTENTS

ACKNOWLEDGEMENTS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF APPENDICES

1. INTRODUCTION AND LITERATURE REWEW

1-1 Introduction

1-2 Literature review 1 -2.1 Agroforestry and intercropping 1.2.2 Nutrient inputs via throughfall. stemflow. litterfall and

dry deposition

2. MATERIALS AND METHODS

2.1 Site description

2.2 Field experirnental design

2.3 Sample collection and preparation 2.3.1 Throughfall 2.3.2 StemfIow 2-3.3 Rainfall 2.3.4 LitterfaIl 2.3.5 Soil nitrogen 2.3.6 Wheat biomass. grain yield and average tillers per plant

2.4 Laboratory analysis 2.4.1 Water 2.4.2 Soil 2.4.3 Plant

2.5 Statistical analysis

3. RESULTS AND DISCUSSION

3.1 LitterfaIl nutrient inputs

3.2 Throughfall nutrient inputs

3.3 Sternflow nutrient inputs

3.4 Nutrient inputs and wheat growth response under tree rows 3-4.1 Nutrient inputs 3.4.2 Wheat growth response

4- CONCLUSIONS

6. APPENDICES

Appendix 1. Seasonal patterns of throughfall for various nutrients in an intercropping system in Southern Ontario. Canada 1997-1 998.

Appendix 2. Seasonal patterns of stemflow for various nutrients in an intercropping system in Southern Ontario. Canada 1997-1 998-

Appendix 3. Modelling nutrient inputs in an intercropping situation in Southern Ontario, Canada,

LIST OF TABLES

Table 1.1. Comparison of macronutrients in stemflow in various forests.

Table 1.2. Cornparison of macronutrients in throughfall in various forests.

Table 1.3. Macronutrient concentrations of the foliage of 15 species of broad-leaved deciduous trees in the Lake Opinicon area of southeastern Ontario (from Ricklefs. 1982).

Table 1.4. Quantities of rnacronutrients in aboveground litterfall in various forests (from Kimmins. 1997).

Table 1.5. Nutrient concentrations of foliar elements in a variety of forest stands.

Table 3.1. Annual Iittërfall biomass distribution by different distances from tree rows under different tree species in the intercropping system. 38

Table 3.2, Nutrient concentrations in the litterfall from different tree species in the intercropping system. 39

Table 3.3. Estimated quantities of annual nutrients returned to ground by litterfall of different tree species in the intercropping system. 41

Table 3.4. Average concentrations of various nutrients in the throughfall from different tree species in the intercropping system. 43

Table 3.5. Estimated quantities of nutrients annually returned to the ground by net throughfall from different tree species in the intercropping system.

Table 3.6. Nutrient concentrations in the sternflow from different

tree species in the intercropping system- 48

Table 3.7. Estimated quantities of nutrients annually returned to the ground by net stemflow from different tree species in the intercropping system. 50

Table 3.8. Annuai nutrient input (kg-ha-') by litterfall, net throughfall and net stemflow in the intercropping systern, 52

Table 3.9. Comparison of nutrient concentrations in 0-20cm soi1 layer at diflerent distances from tree rows under different tree species in the intercropping system. 54

Table 3.10. Estirnated quantities of soi1 nutrient contents (kg-ha") in 0-20cm soi1 layer in different distances from tree rows under different tree species in the intercropping system. 55

Table 3.1 1. Wheat growth response (tillers-plant-') at different distances from tree rows under different tree species in the intercropping system. 57

Table 3.12. Wheat biomass (kg-ha-') at different distances from tree rows under different tree species in thtt intercropping system. 59

Table 3.1 3. Wheat yield (kg-ha-') at different distances from tree rows under different tree species in the intercropping system. 61

Table 3.14. Average total nitrogen concentrations of wheat grain (% dry weight) at different distances from tree rows under different tree species in the intercropping system. 62

Table 3.1 5. Estimated total nitrogen contents of wheat grain (kg-ha-') at different distances from tree rows under different tree species in the intercropping system .

LlST OF FIGURES

Figure 2.1: Field expefimental design used to rneasure throughfall, stemfiow, Iitterfall. soi1 and crop parameters. The design was repeated for 5 tree species. using 5 replications over two years. 30

LlST OF APPENDICES

Appendix 1. Seasonal patterns of throughfall for various nutrients in an intercropping system in Southern Ontario, Canada 1997-1 998.

Appendix 2. Seasonal patterns of stemfiow for various nutrients in an intercropping systern in Southern Ontario, Canada 1997-1 998.

Appendix 3. Modelling nutrient inputs in an intercropping situation in Southern Ontario, Canada-

1. INTRODUCTION AND LITERATURE REVIEW

1 -1 Introduction

This thesis is an investigation of nutrient inputs from trees via throughfall.

stemflow and [itterfall in a temperate intercropping system. The experirnent was

conducted under black walnut (Juglans nigra L), red oak (Quercus mbra L.). silver

maple (Acer sacchannum L.), hybrid poplar (Populus deltoidesxnigra DN 177) and

white ash (Fraxinus amencana L.) plantings with associated crops rotated in corn

(Zea mays L. cv. Pioneer 3917). soybean (Glycine max L.) and winter wheat

(Tntcum aestivum L.). The study was carried out over two field seasons (1 997 and

1998) in a replicated 10-1 2 year old tree intercropped planting at the University of

Guelph Agroforestry Research Station. It is an important component of a larger

investigation of intercropping systems in southern Ontario. Canada.

The hypothesis being examined is that additional nutrients from tree Iitterfall,

throughfall and stemflow may become available to the adjacent crop in addition to

becoming added to the soi1 nutrient pool. In other words, crops among trees rows

might enjoy enhanced nutrient inputs from trees, and may therefore be nutritionally

better than crops grown in a monocropping situation. The research provides

essential data for the management of fertilizer applied to row crops in intercropping

systems. The full use of fertilization via litterfall, throughfall and stemflow can be

achieved by reducing the use of chemical fertilizer, thus protecting the environment

as well as lowering production costs.

To maximize these benefits, an understanding of the complex biological and

ecological interactions that occtir in intercropping systems is currently of the utmost

importance. However, Iittle research on interactions between trees and crops with

respect to nutrient regimes has been conducted in intercropping systems, and

consequently, this study was designed to assess the role of throughfall. sternflow

and Iitterfall in transporthg nutrients from tree rows to adjacent crops and to quantify

these nutrient input fluxes.

1.2 Literature iieview

1 -2.1 Agroforestry and Intercropping

Agroforestry is an integrated land-use management system for production

and farmland conservation. The International Councii for Research in Agroforestry

(ICRAF) has defined agroforestry as "a sustainable management system for land

which increases overall production, combines agricultural crops. tree crops and

forest plants andfor animals simultaneously or sequentially on the sarne unit of land,

and applies management practices which are compatible with the cultural patterns

of the local population" (King. 1979). Based on this definition, there has been a long

history of agroforestry in the temperate zones of the United States and Canada,

Australia and New Zealand, Europe, including the Soviet Union and China.

Windbreaks and silvopastoral systems are the two major types of agroforestry most

commonly utilized in the temperate zone. although there has also been some

interest in systems where trees and crops are integrated (Byington, 1990). Such

integrated systems bridge production agriculture and natural resource conservation

with environmental protection and human needs.

In North America. agroforestry practices include integrated riparian

management systems, silvopastoral (tree-animal) systems. windbreaks and

shelterbelts, alley or intercropping systems, and forest farming (natural

forest/specialty crop). Benefits often attributed to the adaption of agroforestry are

increased crop production, diversified local economies, improved water quality. soi1

erosion and sediment control, filtering and biodegradation of excess nutrients and

pesticides, reduced flood damage, microclimate moderation, and diversified habitats

for wildlife and humans (Gold, 1995). Agroforestry practices can also be used to

protect the quality of the environment by reducing on site degradation processes

and by buffering adjacent areas from the negative impacts of activities in those

areas (Williams, 1993). For example, forest plantations can be used to rehabilitate

degraded fields by reducing soi1 erosion, and improving soi1 organic matter. nutrient

status, and soi1 structure. When planted as a buffer or contour strip, trees can trap

sediment (Williams, 1993). reduce runoff and nutrients in groundwater (Correll,

1983; Daniels and Gilliam, 1996), and shade waterways (Gordon and Kaushik,

1987). Through the selection of the proper species and the application of good

management strategies, increased financial gain can also be realized.

lntercropping or alley-cropping consists of planting trees at spacings that

allow the cultivation of crops among them. In temperate systems, the trees are

usually planted in widely-spaced rows leaving a stnp or "al1eyJy between the rows for

crop production (Gordon and Newman, 1997). lntercropping and related cover

cropping practices have been used to establish forest plantations and to re-

establish natural forest cover in agricultural areas (IMlliams and Gordon. 1992). The

complex interactions among the crop and tree components demands that systems

must be designed carefully so that the plantations will provide the expected benefits

(Gordon and Newman, 1997).

Black walnut is one tree species that has been commonly used in

intercropping systems in North America. Wth this tree species many landowners in

the eastern United States and Canada have adopted a spacing of 12.5m between

tree rows and 3m between trees within rows (270 trees-ha-' ) (Garrett et al.. 1991).

The selection of companion crops is also a critical decision in the design of an

intercroppinglalley-cropping system. At wider spacings, annual crops can be grown

for a number of years. followed by perennial crops such as hay (or pasture) or other

more shade tolerant crops (Gordon and Newman, 1997).

In the tropics. agroforestry. especially fortns involving intercropping, is often

cited as an excellent land-use system because of its productivity. sustainability and

adoptability (Nair. 1993), and many ecological interactions in these tropical systems

have been researched (e.g. Tian. 1992). In temperate systems. much of the early

research on intercropping systems has been concerned with establishment and

4

cultural practices (Gordon and Williams, 1991). More recently. research has been

conducted on the developing interactions found in temperate systems as the trees

age. For exarnple, Williams and Gordon (1995) studied soi1 water potential. soi1 and

air temperature, relative humidity, wind speed and light regimes in clean-weeded

tree rows within crops of corn, soybeans and winter wheat. The growVi patterns of

these crops are different and this ultimately affected environmental and

microclimate conditions within the tree rows and the actual growth of the trees.

Thevathasan and Gordon (1995). working in southern Ontario with a potted poplar-

barley systern, found no difference in the final grain yield (or in other parameters)

between monocropped and intercropped barley. This suggested that poplar was

not in cornpetition for moisture or nitrogen with the barley, and was actually

exploiting a different set of soil resource "horizons". Furthemore, total above ground

biomass produced per pot in the intercropped system was 14% higher than in the

monocropped system.

This study led to further investigations in the field. partially reported on by

Thevathasan and Gordon (1997). The authors investigated soil nitrogen

mineralization and respiration fluxes at regular time and space intervals in the crop

alley-way between adjacent rows of poplar trees in an intercropped field. There was

an increase in N avaiiabiiity due to enhanced N mineralization close to the tree row.

thought to be a result of poplar leaf biomass inputs from shedding trees in the fall.

resulting in a corresponding increase in barley grain N concentration. It was also

noted that there was an increase in the release of CO, from the soi1 profile adjacent

5

to the tree rows as cornpared with the middle of the alley. This was presumably a

result of enhanced root and rnicrobial respiration. Mclean (1990) modelled light

penetration into tree (black walnut and red oak) rows established with corn. and

su bsequent seedling carbon assimilation. He was able to demonstrate differences

in assimilation (initiation and duration) and in the height growth of seedlings,

depending upon the orientation of the rows of corn. Ntayombya and Gordon (1995).

working in southern Ontario with a potted black locust (Robinia pseudoacacia L.)

and barley (Hordeum vulgare, var. OAC Kippen) system, found that intercropping

decreased yiefds of the cornpanion crop. However. they also noted that cultural

practices such as pruning and mulching could moderate yield reductions. In

addition. they found the overall productivity of the black locust-barley system to be

53% higher than that of the sole cropped barley. They were also able to

demonstrate a transfer of nitrogen from the black locust to the barley: barley in the

intercropped treatments showed superior quality and had, on average. 23% higher

grain nitrogen content than sole-cropped barley.

Rhoades et al. (1998) indicate that on highly-weathered Uitisols of the

Georgia (USA) Piedmont, a combination of no-till agriculture and alley cropping

presents an option for rapidly increasing soi1 nitrogen availability while restoring

long-term soi1 fertility. Averaged over a Cmonth study. soi1 nitrate and ammonium

were 2.8 and 1.4 times higher in the alley-cropped than in the treeless no-till plots.

Alley cropping with Albizia (Albizia julibnssin L.) hedges offen Piedmont farmers an

option for reducing reliance upon chemical N fertilizer while improving soi1 organic

6

matter levels. Thevathasan (1 998) has also indicated that intercropping may be one

way in which to reduce N-loadings to adjacent water ways. His prelirninary rnodels

indicate a 50% reduction in N-loadings, largely attributable to the adoption of

intercrop ping practices.

Buresh and Tian (1 998). working in sub-Saharan Africa with trees to improve

soils, found that trees can influence both the supply and availability of nutrients in

the soil. Trees increase the supply of nutrients within the rooting zone of crops

through (1) input of N by biological N,fixation, (2) retrieval of nutrients from below

the rooting zone of crops and (3) reduction in nutrient losses from processes such

as leaching and erosion. Trees can increase the availability of nutrients through

increased release of nutrients from soi1 organic matter (SOM) and recycled organic

residues,

To summarize, agroforestry systems. in addition to providing crop and

income diversification strategies, are often utilized on degraded lands for their soil,

water and nutrient conservation properties (Young, 1989). This is especially true in

the tropics (e.g. Grewal et al., 1994). In contrast, in temperate North America,

agroforestry systems have developed largely as a result of financial considerations,

most likely because the adoption of agroforestry by the farming community is

econornically driven. For example, Ball (1991) working in southern Ontario,

advocated the adoption of nut production and hard wood intercropping as a

potential diversification strategy for tobacco farmers faced with dwindling incomes

from that crop. Nonetheless, there are many conservation and environmental

benefits (e-g. maintenance or enhancement of biological diversity) associated with

the development and adoption of agroforestry systems in North Arnerica, and

recently, some of these benefits have been evaluated in tandem with economic

returns (e-g. Simpson et al., 1994).

1.2.2 Nutrient inputs via throughfall. stemflow. litterfa11 and dry deposition

LitterfaIl. throughfall and stemfiow are the three main pathways through

which nutrients move from trees to surrounding components of the ecosystern. In

intercropping systems, they may also serve as a source of nutrient input to crops

grown adjacent to tree rows. In this section. the major characteristics of these fluxes

and associated pools are discussed -

Stemflow

Stemflow is defined as the concentration of precipitation by leaves and

branches into flow pathways down the stem. Precipitation that reaches the soi1 via

a plant stem (Kimmins, 1997). In north temperate systems. stemflow is a function

of stand density, canopy size. precipitation regime, bark roughness, canopy holding

capacity and other factors. (Kimmins. 1997; Perry, 1 994; Voigt, 1960).

The absolute amount of interception loss is relatively independent of storm

size since it is determined by interception storage capacity, which is more or less

constant. By the same argument, interception loss becomes a decreasing

percentage of total precipitation as storm size increases. Interception storage for

8

tree and shrub cover has been reported to range between 0.25 and 7.6 mm of rain

and up to 2.5 cm (water equivalent) of snow (Satteriund. 1972). Interception loss of

rain attributed to trees can range from 100% for light summer showers in dry

climates to 0% for heavy or continuous winter rain in humid climates. It is much

reduced in deciduous trees in the nonleafy period.

Water intercepted by tree crowns is redistributed into two major subtypes and

reaches the fioor very non-uniformly: throughfall and stemflow. The importance of

sternflow varies greatly. Immature forests, forests of hardwoods such as cherry

(Prunus spp. L.) or alder (Alnus mbra Bong. ; Alnus sinuata (Rage) Rydd.). and

forests of coniferous species such as pine (Pinus spp.) tend to have more stemflow

because their upturned branches act as a funnel. Stemflow also varies with stand

density. For exarnp le, an 1 8-year-old Doug las-fir (Pseudotsuga menziesii (Mirb)

Franco.) spacing plantation near Vancouver. B.C. (Kimmins, unpublished data).

revealed that interception loss varied from 15 to 26% of incident precipitation as the

number of trees per hectare decreased from about 10.000 to 730, and that the

relative proportions of stemfiow to throughfall declined from 44% (Le. 44% of the

water reaching the ground beneath the trees was sternflow) in the most dense stand

to 3% in the least dense stand. This difference was attributed to differences in

crown morphology.

Tree species with pendulous branches tend to have little stemflow and

redistribute much of the incident precipitation into canopy-edge drip. Species with

erect or acute-angled branches have much more stemflow and less canopy drip.

9

The closer the spacing in many stands. the higher the proportion of acute-angled

branches and the greater the importance of stemflow (Kimmins. 1987). Stemfiow

is also affected by bark roughness. Smooth-barked species have little stem water

storage capacity. and stemflow will commence on smooth-barked species such as

beech (Fagus grandifolia Ehrh.) after only slightly more than 1 mm of rain has fallen

(Voigt, 2 960; Leonard, 1961). Rough-barked species such as spruce (e-g. Picea

spp.) and other conifers often have a rarge stem storage capacity, and appreciable

stemflow rnay not reach the ground until more than 2 cm of rain has fallen (Helvey

and Patric, 1965; Chourmouzis, 1995). The amount of water arriving via stemflow

per unit area over a small area close to the tree bases has been found to be up to

seven times that of the incident precipitation (Gersper and Holowaychuk. 1970).

Quantitative contributions of stemflow to overall nutrient cycling are srnall

and often limited to small distances (about 30cm) from the tree base (Voigt. 1960a;

Cole et al., 1967; Mahendrappa and Ogden 1973b). although the overall effects of

stemfiow can be significant in some circumstances (Mina, 1965; 1967). Where

stemflow is appreciable, it serves to concentrate a lot of the incident precipitation

close to the base of the trees. For example, in a study of the distribution of

radioactive fall-out in the soi1 beneath beech trees in Ohio, it was found that soi1 at

the base of a tree where there was abundant stemflow contained five times as

much radioactivity as soi1 where there was no stemflow.

Acidified stemflow of some tree species has lowered soi1 pH around tree

stem (Matsura et al., 1991). and the stemflow pH of urban street trees has been

10

found to be higher than that of some suburban trees. One of the possible reasons

for higher pH is neutralization by higher concentrations of K', Ca2+ and ~ g ~ ' in the

stemfiow (Takagi et al., 1997). It has also been suggested that the quality and

quantity of stemfiow and throug hfall from individual trees can also influence soi1

properties (Zinke, 1962).

Many researchen have quantified nutrient additions and changes in nutrient

concentrations in stemflow (Cole et al.. 1967; Carlisle et al.. 1967; Duvigneaud and

Denaeyer-DeSmet, 1970; Eaton et al.. 1973; Mahendrappa. 1974; Malkonen,l974;

Torrenneva, 1975; Verry and Timmons, 1 976; Tang, 1 996; Li et al.. 1 997; Whifford

et al., 1997; Takagi et al., 1997; Oyarzun et al., 1998). However, there is still a great

need for information on the chernical composition of stemfiow from different tree

species in Canada and their influence on the soi1 properties (Foster and Gessel.

1 972).

Sternflow has been shown to contribute 0.0-1 -1 kg - ha-'- yrl N, 0.0-0.1 kg

- ha-'- yr-' P, 0.2-7.2 kg ha-'- yfl K, 0.4-6.2 kg - ha*'- yrl Ca. and 0.24.8 kg - ha-'.

yr-' Mg in nutrient returns to various forest types (Table 1.1 ) (Kirnmins, 1 997).

There appear to be no reports concerning the chemistry of sternflow in

intercropping systems.

Throug hfall

Throughfall is defined as precipitation that either falls to the soi1 surface

directly through gaps in the canopy, or drips from branches and foliage (Kirnrnins.

11

1997). In north temperate systerns, throughfall is a function of stand density, canopy

size, precipitation, holding capacity and many other factors (Kimmins, 1997; Perry,

1994)-

The nutrient content of throughfall rnay either decrease or increase on its

way through the canopy. Decreases reflect direct absorption by foliage or foliar

epiphytes (including lichens, fungi. and bacteria). However, increases are more

commonly reported than decreases and result from: a. nutrients that have collected

on foliage through dryfall, and b. nutrients leaching from foliage or foliar epiphytes.

The former is an input to the system, while the latter is part of the intrasystem cycle.

It is very difficult to distinguish between these two sources (Perry, 1 994).

Temperate and tropical forests growing on relatively fertile soils mostly add

nutrients to precipitation. Forests g rowing on highly infertile soils, however, often

scrounge cations and phosphorus (the most Iimiting nutrients in many tropical

systems) from rainfall as it passes through the canopy (Duvignead and DeSmet,

1 970; Jordon et al.. 1982; Brasell and Sinclair, 1983).

Any nutrient may be leached from tree canopies by rainfall as long as it is in

soluble form. However, the basic cations are usually more prevalent in throughfall

than nitrogen and phosphorus. This is particularly true for potassium. which is not

known to occur in organic forms within tissues (Duvignead and DeSmet, 1970;

Jordon et al., 1982; Brasell and Sinclair, 1983). The potassium content of

precipitation is often increased 10-fold by passage through the canopy

(Gooley, 1983).

lntracycle nutnents in throughfall may corne primarily from canopy

components other than leaves. Reiners and Olsen (1 984), for example. studied

nutrient fluxes to and from various parts of balsam fir (Abies balsamea (L.) Mill.)

canopies and found that dead twigs and lichens growing on twigs added well more

than 10 times the amounts of sulfate and potassium to precipitation water than were

added by foliage. On the other hand. lichens were a strong sink for ammonium and

nitrate in precipitation. Active nutrient release by dead twigs to precipitation water

may explain why calcium, which is quite immobile in living tissues, sometimes

occurs in rather high concentrations in throughfall.

Throughfall is a major component of nutrient input and cycling in forest

ecosysterns. Many researches have quantified nutrient additions and changes in

nutrient concentrations in throughfall as a result of passage through forest canopies

(Nye, 1961 ; Attiwill, 1966; Carlisle et al., 1965,1967; Brown et al-, 1 970; Denaeyer-

DeSmet, 1 970; Wells et al., 1972; Reiners, 1972; Abee and Lavender, 1 972; Hart

et al., 1973; Eaton et al., i 973; Malkonen, 1974; Torrenneva, 1975; Henderson,

1977; McColl et al., 1978; Sigmon et al., 1989; Arthur, 1992; Blew et al., 1993;

Matzner et al., 1994; Amezaga et al., 1996; Fenn et al., 1997; Lin et al., 1997), and

much attention is being focused on the extemal and interna1 sources of throughfall

enrichment (Parker, 1983). Throughfall deposition collection rernains a useful tool

for quantiQing the input of elements from atmospheric deposition to the forest soi1

(Hovrnand et al., 1995; Butler et al., 1995).

Throug hfall has been shown to contribute 0.9-1 1 .O kg - ha-'= yrl N, 0.3-2.7

14

kg - ha-'- y s P. 4.1-1 96.0 kg - ha-'- yr-' K. 2.0-26.0 kg - ha-'- yr-' Ca, 0.4-16.0 kg

ha-'- yr' Mg in nutrient returns to various forests types (Table 1.2) (Kirnmins. 1997).

There appear to be no reports concerning the chemistry of the throughfall in

intercropping systems.

Litterfal l

Litterfall is defined as Ieaves. branches and bark that are annually shed from

trees. Litterfall studies have largely focused on aboveground litterfall processes,

although the few data that are available suggest that in most forest ecosystemç. the

death of roots and mycorrhiza may account for two thirds or more of the narogen

returned to the soi1 in plant litter (Cole and Rapp, 1981 ; Vogt et al-, 1986).

The return of nutrients frorn the tree component of the forest to the soi1

provides an important source of nutrients for replenishing the soi1 and ensuring

availability for further plant developrnent. Litterfail from the forest canopy is often the

major contributor of N to the soi1 system (e.g. Foster. 1972) but is also important

as the source of the majorÏty of the nutrients taken up annually by plants (e-g. P. Ca.

Mg). Decomposing Iitter forms a superficial organic layer that plays an important

role in the protection of soi1 against erosion and in regulating soi1 moisture status

(Kimrnins. 1997). Litterfall generally accounts for the majority of the nitrogen,

calcium, and magnesium loss from standing vegetation. and leaching generally

accounts for the majority of the potassium loss. The major pathway of phosphorus

loss is occasionally Iitterfall and sometimes leaching (Kimmins. 1997).

15

The litterfall component of the nutrient cycle has been studied in many

conifer and hardwood forests (e.g. Madgwick and Ovington, 1959; Will, 1959; Nye.

1961 ; Ovington, 1962; Bray et al., 1964; Carlisle et al., 1966. 1967; Cole et al..

1967; Durigneaud and Denaeyer-DeSmet. 1970; Hegyi, 1972; Gosz et al., 1972;

Foster and Gessel. 1 972; Abee and Lavender, 1 972; Nihlgard. 1972; Foster. 1 972.

1 974, Morrison, 1973, 1974; Malkonen, 1974; Ashton, 1975; Attiwill, 1978; Lee,

1978; Binkley, 1982; Baker. 1983; Nair. 1984; Sharrna. 1989: Zhang. 1990;

Crockford et al., 1 997; Santamaria, 1998; Crockford et al-. 1998).

Table 1.3 and Table 1.4 present a summary of the quantities of selected

rnacronutrients transferred from trees to soi1 by aboveground litterfall. The quantity

is a function of the biomass, the type (leaves, branches. bark. etc.), and the nutrient

concentrations in the litterfall , al1 of which Vary from site to site. Litterfall losses are

generally greatest on moist, warm. fertile, and other high-productivity sites and least

on dry, cold, infertile, and other low-productivity sites.

Litterfall has been shown to contribute 11-228 kg - ha4- yr ' N; 0.2-9.0

kg ha-'. yrl P; 2.5-103 kg - ha-'- yrl K; 7-0-206 kg - ha". yrl Ca; 1.145 kg ha"-

yfl Mg in nutrient retums to various forest types (Table 1.3) (Ricklefs et al.. 1982).

(Table 1 -4) (Kimmins, 1 997)-

Wth the exception of Thevathasan and Gordon (1 997). who studied litterfall

-N inputs in a poplar-barley system, there appear to be no reports concerning the

chemistry of litterfall in intercropping systems.

Table 1.3. Macronutrient concentrations of the foliage of 15 species of broad- leaved deciduous trees in the Lake Opinicon area of southeastern Ontario (from Ricklefs, 1982).

Macronutrient concentrations (percent dry weight) Species N P K Ca Mg Fag aceae

Fagus grandifolia 2- 1 (beech) 1.9

1-8 Quercus alba L- 2.2

(white oak) 1-9 1-8

Quercus ruba 1.8 (red oak) 1 -8

1.8 Quercus marcrocarpa Michx. 2.1

(bur oak) 2-1 2.1

Aceraceae Acer negundo L- 2.5

(Manitoba maple) 2.7 2-4

Acer pensylvanicum L. 1.9 (striped map le) 1 -6

1.3 Acer rubrum L- 2-0

(red maple) 1.5 1.4

Acer saccharum Marsh. 2.2 (sugar maple) 1.5

1 -7 Oleaceae

Fraxinus amencana 2.1 (white ash) 1-9

1 -6 Fraxinus nigra Ma rs h . 2- 1

(black ash) 2- 1 1.7

Fraxinus pennsylvanica Marsh. 1 -8 (red ash) 1.8

1 -4

Table 1.3, (Continued).

Species Macronutrient concentrations (percent dry weight)

N P K Ca Mg - - - -

Saliaceae Populus balsamifera L. 2-0 0.29 0-88 0-75 0-32

(balsam poplar) 1 -9 0.29 0.73 0.84 0-25 1 -6 0.20 0-51 0-65 0-24

Populus deltoïdes Bartr. 2-4 0.23 1.19 0-70 0-17 (eastern cotton wood) 2.3 0.19 0.44 0.92 0.20

1 -9 0.14 1-36 0.86 0-20 Pop ulus grandiden tata M ic hx- 2-5 0.24 4-36 0.86 0.20

(big-toothed aspen) 2-4 0.18 0-59 0.70 0.30 2.2 0.18 0-49 0-62 0-22

Populus tremuloides Michx, 2.6 0.24 0-61 0-54 0-19 (trembling aspen) 2- 1 0-17 0-76 0-83 0-26

2- 1 0.17 0.63 0-94 0-26

Table 1 -4. Quantities of rnacronutrients in aboveground litterfail in various forests (from Kimrnins, 1 997).

N P K Ca Mg Location (kg-ha-'-yP') Reference

2-5 7.8 - Malkonen, - 1974 Scots pine, Finland

Doug las-fir, Washington

Jack pine, Ontario

Canada

Douglas-fir, Oregon

Nothofagus forest.

New Zealand

Oak forest, England

Oak forest, Belgium

Spruce, U S S R -

Hardwood forest, N.H-

Loblolly pine, N.C.

Oak forest, U.S.S.R.

Birch forest, U.S.S.R.

Beech, Sweden

Red alder, B.C. Canada

Tropical forest, Ghana

Cole et ai-, 1967

Foster and Gessei,

1972

Abee and Lavender,

1972

Ovington, 1 962

Carlisle et al., 1966

Duvigneaud and

Denaeyer-DeSmet,

1970 -

Ovington, 1962

Gosz et al-, 1972

Ovington, 1962

Ovington, 1 962

Ovington, 1 962

Nihlgard. 1972

Binkley, 1 982

Nye, 1961

Leaves are the major component of aboveground Iitterfall in most

ecosystems (Kimmins, 1997). and the nutritional status of tree leaves provides an

important diagnostic tool for establishing their condition (Innes, 1993; Wyttenbach

et al., 1995). While most studies have concentrated on identifying deficiencies.

excesses may also occur, particularly with nitrogen, sulphur and some heavy metals

(Bergman, 1993; Breckle et al., 1992). Major problems occur when comparing foliar

nutrient concentrations in trees in different areas and through tirne because of the

spatial and temporal variation of nutrient concentrations (Helmisaari, 1990: Santene

et al., 1990)- ln addition, the nutritional status of forest trees has only been

established for some species and the nutrient dynamics of other tree species

remain virtually unknown (Santamaria and Martin, 1998).

A summary of the variation in foliar nutrient concentrations in some tree

species is given in Table 1 -5. Over a two year period (1 992-1 993), foliage samples

from different tree specks were taken in 17 forest stands located in Navarre. Spain.

Samples were analysed for Ca, Cd, Cu, Fe, K, Mg, Mn, N, Na, P. Pb, S. and Zn.

The health of the sampled trees was also assessed by determining the degree of

defoliation and discolouration of the canopies (Santarnaria and Martin, 1998).

Strong relationships between f~ l i a r nutrient concentration and stand

productivity have been reported for various tree species (Van Cleve et al.. 1983;

Allen and Gillespie, 1991). These relationships are of great importance in

quantifying canopy-scale processes on a landscape level. For example, canopy

nitrogen (N) content has been shown to be correlated with aboveground net primary

31

Table 1.5. Nutrient concentrations of foliar elernents in a variety of forest stands (after Santarnaria and Martin, 1 998). - Macroelements (rngag'l) @ Microelements (vg#gs1)

Stand Species Ca K Mg N P S Cd Cu Fe Mn Na Pb Zn 1 Quercusrobur 12,3 13,6 2.1 26,9 25 2,4 0,05 10.0 163 977 491 1.5 27 2 llexaquifolium 13,O 153 2,7 29,O 2.2 1.7 0.24 6,9 81 983 127 0,8 104

3 Quercusrobur 17.3 9,3 2.5 19.1 2.5 2,3 0,05 8.6 143 622 224 1,3 16 4, Fagus sylvatica

8 5 ~ a g u s sy~vatica 6 Fagus sylvatica 7 Pinus sylvestris 8 Qther deciduous* 9 Pinus sylvestris 1 O Fagus sylvatica 11 Fagus sylvatica 12 Quercus ilex 1 3 Quercus ilex 14 Pinus sylvestris 15 Quercus faginea 16 Pinus nigra 8 5 6,O 1.8 12,3 2,l 1.2 0,04 4,6 30 31 17 0,7 26 17 Quercus ilex 20,O 6.8 1,7 17.0 2.0 1.8 0.06 6,5 137 181 77 1.0 22

* Acer Campestre, Corylus avellana and Fraxinus excelsior

productivity across a variety of coniferous and deciduous forests (Birk and Vtousek.

1986; Matson et al., 1994). This relationship is not surprising considering that foliar

nutrients. particularly N and P. influence the photosynthetic capacity of leaves and

thereby overall canopy photosynthesis (Linder and Rook. 1984; Field and Mooney,

1986; Foyer and Spencer. 1986). However, the strength of the relationship varies

depending on whether a mass or area-based expression (either nutrients or

photosynthesis) is utilized (Reich and Walters, 1994; Reich et al., 1995). The

photosynthetic capacity of leaves and canopies normally changes along gradients

of varying resource (light, water, and nutrients) availability (Field, 1991). and this

has been associated mainly with changes in canopy specific leaf area (SLA, Leaf

area per unit mass) (Gutschick and Wiegel. 1988; Brand. 1987; Running et al.,

1986). Many researchers have reported on the relationship between nutrient

concentration and growth response for various tree species (Grier et al., 1981 ; Van

Cleve et al., 1983; Pastor et al., 1984; Bowen et al.. 1984; Waring et al.. 1985;

Mclaughlin et al.. 1985; Nambiar et al., 1987; Mitchell, 1 990: lngested et al.. 1991;

Slapokas et al., 1991), but Iittle, if any information exists on the crop growth

response or productivity under plantations in intercropping systems.

Dry Deposition

Nutrients contained in dust and gases that are present on leaf surface are

solubilized and become part of throughfall. A heterogeneous mixture of gases and

aerosols are either raked from horizontally moving air masses by the canopy or (in

the case of large aerosols) seffle ont0 canopy surfaces under the influence of

gravity. Collectively referred to as dry deposition, these represent a significant

pathway by which nutrients and other elements are added to local ecosystems. In

forests that are periodically immersed in clouds or fog, elements are additionally

deposited on canopy surfaces along with water droplet (Perry, 1994)-

Dryfall is used to describe the transfer of atmospheric gases and dust to

surfaces. such as tree crowns which very effectively remove gases and dust from

atrnosphere. This is both good news and bad news for trees. Dryfall rnay provide

an important source of nutrients, but in the industrial northern hemisphere, an

increasing proportion of dryfall over the past few decades has been pollutants

(Perry, 1 994).

In areas with polluted air or high levels of atmospheric dust from natural

sources (e.g. sites that are downwind from deserts or agricultural lands). significant

amounts of some elements are added to ecosystems through dry deposition. In

addition to gases, nutrients are input from the atrnosphere to forests as constituents

of aerosols, particles ranging from 5 mm to 20 prn in size. At least 77 different

elernents have been detected in atmospheric dust, including al1 of the essential

plant and animal nutrients. (Bowen (1 979) presents data on the aerosol composition

of the atmosphere at various points across the globe). Aerosols are readily washed

out of the atmosphere by precipitation and may also be deposited on canopy

surfaces by condensation.

Much of the atmospheric input of sulfur and nitrogen (excluding the biological

fixation of N2) is derived from gases- nitrogen frorn nitrous oxides and ammonia. and

sulfur from sulfur dioxide. These react chernically with foliar or soi1 surfaces in a

process that is greatly facilitated if the gases are dissolved in water. Nitrogen and

sulfur are transferred from the atmosphere to foliar surfaces with particular

efficiency in forests that are frequently enshrouded in clouds or fog (Lovett et al.,

1982) and from the atrnosphere to surface soi1 layers when they are wet

(Hanawalt 1969a. 1969b). Malo and Purvis (1964) estimated that 20-60 kg - ha-'-

yr ' of nitrogen were absorbed as ammonia (NH,) in the New Jersey soils they

studied and Young (1964) similarly found that NH, was absorbed in Pacific

Northwest soils-

These values do not represent a net nitrogen increment to the ecosystem,

since NH, is also released frorn canopies and soils to the atmosphere. Whether a

given forest (or any vegetation type) absorbs more NH, than it releases or vice

versa, depends at least in part on atmospheric concentrations of the element.

Recent work by Langford and Fehsenfeld (1 992) in the rnontane forests of Colorado

shows that when atrnospheric NH, concentrations were low, forest canopies

released more NH, to the atmosphere than they took up. When atmospheric

concentrations were high. net transfer was in the opposite direction (Le. from the

atmosphere to forest). In some areas, atmospheric concentrations rnay be high

enough to produce net transfer to forests only when winds were from agricultural

areas. Since NH, is volatilized from animal wastes and fertilizers, agriculture is

believed to be a significant source of NH, and acid rain in Europe.

25

Calcium. potassium, and rnagnesium are major constituents of dry deposition

in both temperate and tropical forests (Jordan, 1982; Swank and Henderson,

1976;Ulrich et al., 1981). Between 1969 and 1972 in one German beech forest, the

proportion of total atmospheric inputs accounted for by dryfall ranged from 0% for

phosphorus to 78% for potassium and 89% for manganese (Ulrich et al., 1981).

Proportions of dry input for the other nutrients were generally on the order of 30%

to 50%. ln contrast. dry deposition accounted for 20% of the atmospheric

phosphorus inputs to a Caribbean pine forest in Belize but only 8% and 9% of the

potassium and calcium, respectively (Kellman and Carty. 1986).

Nutrients deposited on canopies may be absorbed before they are washed

to the ground (particularly elements that are in short supply). In a mixed hardwood

forest in the eastem United States, dry deposition was estimated to account for 56%

of the total atmospheric inputs of sulfate and inorganic nitrogen (Le., nitrate and

amrnonia). 59% of the potassium, and 67% of the calcium (Lindberg et al., 1986).

In that study, 7% of the deposited nitrogen was retained in the canopy, probably

absorbed directly by foliage or epiphytes growing on the foliage. Most of the acidity

(Le., H' ions) accompanying the nitric and sulfuric acids that composed a high

proportion of the dry deposition to that site were also absorbed by foliage with an

accompanying release of calcium and potassium ions from foliage. Direct

absorption of nutrients by leaves and canopy epiphytes has been shown to be quite

important on nutrient-poor sites in Amazonia (Jordan et al., 1979).

In summary. the amount of nutrients added to ecosystems from the

26

atmosphere is extremely difficult to measure accurately. particularly in areas that

are impacted by acid rain. Most available data on atmospheric inputs are based on

the nutrient content of bulk precipitation, and do not account for deposition on

canopy and soi1 surfaces. Such values probably underestimate total atmospheric

inputs by 10% to 90% depending on the nutrient in question and the local

ecosystem. The difficulty of rnaking accurate measurements is fu rther compounded

by the fact that in at least some ecosystems, significant amounts of nutrients are

directly absorbed by canopies and hence never appear in collectors on the ground.

On the other hand, many of the nutrients that are captured in collectors placed

beneath canopies do not represent inputs from the atmosphere but rather are

leached from foliage. Leaching of cations from foliage occurs in al1 forests, but is

particularly prevalent in areas with acid rain (Perry, 1994).

2. MATERIALS AND METHODS

2.1 Site Description

The study was conducted at the University of Guelph Agroforestry Research

Station in southern Ontario (43' 16' 30" N. 8 9 O 26' 35" W), at an elevation of 340rn.

Mean annual precipitation at this site is 702mrn. The mean frost free period is 136

days and the mean annual temperature is 6.65OC with average highest

temperatures of 25.5OC in July and average lowest temperatures of -12.2% in

January. The temperature extremes range from -33OC to 38OC. The soi1 type is

sandy loam (Luvisolic order, grey brown luvisols great group, Can. Syst. Soil Class..

1974) with A-horizon depths between 28 and 53cm. All cultural practices (land

preparation, seed rate, weed control and fertilizer application) were the same for

al1 growing seasons in the overall study. The land was zero-tilled. During the study

period the field was fertilized at the rate of 45 kg N ha" during the last week of April.

The site was used for continuous hay production prior to the initiation of the

overall intercropping study in 1987. Annual crop production prior to this time had

been in decline and soi1 erosion was becoming a serious problern. The first tree

planting was established in 1987 with row spacings of 12.5m and 15.0m. parallel to

the crop rows, and within row spacings of 5m and 6.25m. Trees were lower stem-

pruned on an ad hoc basis during the initial years.

Since 1990, three annuai crops have been grown under normal rotation

between the tree rows at the site: corn. soybean and winter wheat. The main tree

species at the study site hclude black walnut, hybrid poplar, silver maple. red

maple, red oak, white ash, Nonnray spnice (Picea abies (L.) Karst.) and eastern

white cedar (Thuja occidentalis L.).

2.2 Field Experimental Design

The current experiment was conducted in an intercropped field with wheat-

tree, and soybean-tree combinations at the Agroforestry Research Station. Guelph.

Treatments included five tree species - black walnut, red oak, hybrid poplar, white

ash and silver maple. Five trees were randomly selected (within existing designs)

for each tree species (total 25 trees) for throughfall and stemfiow collection. At each

tree. three sampling plots were established at distances of lm, 3.5m and 6m from

the tree row for the collection of soil, Iitterfall and crop (wheat) biomass and yield

data. The data was collected over two years (1 997. 1998). Data was analysed as

a 3 (distance from tree row) x 5 (species) factorial design. The layout of the

experiment is shown in Figure 2.1.

2.3 Sample Collection and Preparation

2.3.1 Throug hfall

Throughfall was collected from beneath the overhanging tree canopy and

removed within 24 hours of the end of each rainfall event from July to November

29

*w O min gauges

tree row

and stemflow samplers

6m )/sampiing points

- litterfail, soi1

and crop parameters

Figure 2.1. Field experimental design used to measure throughfall, stemflow. litterfall, soi1 and crop parameters. The design was repeated for 5 tree species, using 5 replications over two years.

1997 (14 rainfall events), and from May to June 1998 (6 rainfall events) using 25

throughfall collection gauges (5 species x 5 replications). 50ml water was collected

for each of 25 samples fiom each rainfall event. The pH and volume of each sarnple

were detemined on site using a Digi-Sense Model 5985-80 pH meter and

volumetric cylinder respectively. Residual water was poured around the tree base

after each measuring and sarnpling. By the end of the 1997 sampling season.

snowfall had comrnenced and 50 to 100% of the leaves had been shed from the five

identified tree species. Sarnples were placed in a cooler box with ice. transferred

to the lab and stored at -20% in the dark until analysed for nutrient content.

Throughfall collectors consisted of rnodified Plastmo K-snap eaves trough,

lOcm in width and 75cm ni length with a catchment ares of 750cm2. Polyethylene

tubing connected the troughs to 5-10 litre jugs, depending on species of the

sarnpled trees; nylon screening was also inserted into the link between the tubing

and trough in order to prevent the entiy of foreign matter. The throughfall collectors

were mounted on frarnes (about 0.5m in height) and inclined gently to the tubing

end. After each sampling, collectors and screening rolls were cleaned using water.

2.3.2. Stemflow

Stemflow was intercepted using spiral collars of spl iit vinyl tubing and grav ity

fed through intact tubing into plastic receptacles at the base of the trees after each

rainfall event A total of 25 trees received collas. The height of the lower end of the

collar varied from 0.3-0.5m above ground level, depending on the shape of the tree

base. To ensure total stemflow interception an adhesive (Silicone II) was used to

seal the coliar to the stem- 50mf water was collected for each of 25 samples from

each rainfall event. Nylon screening was also inserted into the link between the

collar and receptacle in order to prevent the entry of foreign matter. The pH and

volume of each stemfiow sample was deterrnined on site using a Digi-Sense Model

5985-80 pH rneter and volumetric cylinder respectively and then the rest of the

water was poured around the tree base. Stemflow samplings were conducted at the

same time as throughfall collection. The samples were placed in a cooler box with

ice, transferred to the lab and stored at -20°C in the dark until analysed.

2.3.3. Rainfall

Rainfall was collected after each rainfall event using four funnel-type

collectors that were constructed using 5-litre bottles with a 140crnZ catch area

plastic funnel fitted to the top of the bottle. A nylon screen roll was inserted in the

connecting stem between funnel and bottle to prevent foreign matter (leaves, insect

frass, etc.) from entering. The funnel-bottles were then attached on raised stands

(1 -5m) and placed in an open area away from any obvious influence of canopies of

trees and crops. Precipitation sarnplings (four at each collection) were conducted

at the same time as stemflow and throughfall. The sarnples were placed in a cooler

box with ice, transferred to the lab and stored at -20°C in the dark until analysed-

2.3.4. LitterfaIl

Leaf biomass distribution on the study site was assessed at 3 distances (1 m.

3.5m and 6m) from the 25 sarnpling trees by setting up 75 litterfall traps. These

were located on the northeastern side of the tree rows due to the prevailing wind

direction. The traps were 2m in length paralleling tree row and l m in width, the

boundary which closed to the tree row was 1.0m from the tree row. They were fixed

on the ground using stakes; Iitterfall collected in traps was removed by hand so that

the sarnples rernained intact prior to analysis- LitterfaIl collections began at the

beginning of leaf shedding in later September and conti~ued to the end of shedding

in early December 1997. In order to avoid decay of the shed leaves, the collections

were conducted once or twice a week depending upon the humidity and

temperature between collection periods-

The samples from each trap were air dried, mixed completely, and then

stored in open-top paper bags. Samples were then placed into the drying oven for

48 hours at 65*C, dried, and then weighed for biomass. About 209 litterfall from

each sample was taken and ground in a Wiley miIl for nutrient analysis.

2.3.5 Soil nitrogen

Total nitrogen: About 100-2009 of field moist soi1 for each of 75 samples was

collected from a depth of 0-20cm on July 16, 1997 at 3 distances, 1 m. 3.5m and

6m, from 25 sampling trees. The soi1 was air dried and woody debris were removed

by hand. Air dried soi1 samples were then ground in a grinder and sieved through

a 2mrn screen. The samples were placed in the drying oven for 48 hrs at 65OC

33

before digestion.

lnorganic nitrogen: About 100 to 2009 of field moist soi1 for each sample was

collected from a depth of 0-20cm at the same locations as for total nitrogen

sarnpling. Sampling was on a monthly basis starting in June and ending in August

1998. Soil sampling was collected hnro days after a substantial rainfall event. Soil

was mixed well and free of any woody debris. Soil samples were placed in a cooler

box with ice, transferred to the lab and kept frozen at -20°C until extraction for NO,-

N and NH,-N.

2.3.6 Wheat biomass, grain yield, and average tillers per plant

Total above ground wheat biomass, grain yield and average tillers per plant

were assessed several days before crops were harvested. Data were collected in

both 1997 and 1998-

From the same locations where Iitterfall and soi1 samples were collected,

wheat plants (including roots) were removed within a sample area of 2m by 0.2m.

A total of 75 samples were collected. After the number of plants and the tillers per

plant were counted, wheat roots were removed and then samples were placed in

paper bags and dried in a drying oven at 60-70°C for 2-4 days. Dried samples were

weighed for biomass. Grain was shelled and weighed for yield. Appraximately 209

of grain was ground for nutrient analysis.

2.4 Laboratory Analysis

2.4.1 Water

Throughfall, stemflow and rainfall samples were thawed and filtered through

Whatman No.2 filter paper before analysis. N and P concentrations were

determined using a Technicon Autoanalyzer II Systern, and K, Ca and Mg were

determined using fiame analysis on a Varian Spectra AA-300 Atomic Absorption

Spectrorneter (Va rian Associates, Sunnyvale, CA).

2-4-2 Soil

1) Total nitrogen

Soil and grain samples were digested using the Kjeldahl Method and then

total nitrogen was analysed using a Technicon Autoanalyzer II System (Technicon

Industrial System, Tarrytown, N.Y.).

2) Inorganic nitrogen (NO,-N and NH,-N)

Samples were allowed to thaw in order to re-incorporate the moisture inside

the bags before extraction with 2N KCI. 209 of soi1 was extracted with 60ml of 2N

KCI in a 100ml clear snap via1 by shaking on a mechanical shaker for one hour

(Keeney and Nelson, 1982). In order to determine the moisture content of the

samples, another sub-sample of soi1 was taken from each sample and oven-dried

at 105°C for 48 to 72 hours. The calculated moisture contents were then used to

35

convert ppm nitrate to a dry soi1 weight basis (pgll00g soil). Extracts were analysed

on a Technicon Autoanalyzer II system.

2.4.3 Plant

Total nitrogen on litterfaIl and wheat grain was done using standard Kjeldahl

methods and then analysed using a Technicon Autoanalyzer II System.

Total P, K, Ca and Mg were done using the Dry Ash digestion rnethod

(Gavlak, 1997) and then analysed using a Technicon Autoanalyzer II system for P

and flame analysis on a Varian Spectra AA-300 Atomic Absorption Spectrometer

for K, Ca and Mg,

2.5 Statistical Analysis

Statistical analysis was conducted using SPSS 7.5 for Windows (General

Linear Model-General Factorial, Normal probability plots, Data transformations, etc.)

and Microsoft Excel 7.0 for Windows 95 (data organization, graphie).

3. RESULTS AND DISCUSSION

3.1 LitterfaIl nutrient inputs

The annual Iitterfall biomass (g-m-2) distribution at different distances frorn

the tree rows under different tree species in the studied intercropping system is

shown in Table 3.1. The Iitterfall biornass from different tree species is significantly

different at pl; 0.05: silver maple = hybrid poplar > red oak = white ash > black

walnut.

For al1 species, litterfall biomass between 1.0m to 2.0m from the tree row was

greater than litterfall at a distance of 6.0m to 7.0m. For walnut. this difference was

5.66 times, for red oak, 3.1 1 times, for silver maple, 2.93 times, for Hybrid poplar.

2.07 times, for white ash, 12-68 times.

Some between species differences were also apparent. For example.

regardless of distance from tree row, litterfall (g-m-2) was always greatest under

silver maple and hybrid poplar compared to the other species. The lowest litterfall

was found under black walnut,

The mean concentrations of the major elements in the Iitter are shown in

Table 3.2. Leaves from black walnut and silver maple had the highest litterfall N

concentration. For P. K, Ca and Mg, no obvious trends were found with 4 of the 5

species (not the same ones) exhibiting similar leaf nutrient concentrations.

Table 3.1. Annual litterfall biornass (g~rn'~) distributions by different distances from tree rows under different tree species in the intercropping system.

LitterfaIl biomass (gm2 I SD) in distances from tree rows

Btack walnut 24.261 4.05 a (a) 8.5512.79 a (b) 4.2910.58 a (b)

Red oak 1 07.27121.86 b (a) 46.9511 3.17 b (b) 34,4714.47 b (b)

Silver maple 191,47132.57 c (a) 99.89118.90 c (b) 65.40114.68 c (b)

Hybrid poplar 161.4718.95 c (a) 105.77113.12 c (b) 78.0215.63 c (c)

White ash 113,58129.46 b (a) 40.5914.94 b (b) 8.9611.69 a (c)

Values followed by the sarne letter by column across species and (row) across distances are not significantly different at ps0.05.

Table 3.2. Nnutrient concentrations in the litterfaII from different tree species in the intercropping system -

Concentrations of nutrients (% dry weight * SD) Species

N P K Ca Mg Black walnut 1,401 0.121 O -405 2-466 0.61 5

10,079 a k0.007 a *O-034 ab i0-076 a 10.070 a

Red oak 0-740 0.056 0-297 1,735 0-520 i0-077 b *O-015 b 10.043 a k0.325 abc 10.126 a

Silver rnaple 1-286 0.084 0-264 1,305 0.21 0 10,131 ac 10.047 ab 10.155 a 0,731 b *O-121 b

Hybrid poplar 0.956 0.093 0-476 2-469 0.631 k0.077 d *O-009 ab 10.056 b 0-396 ac 10-052 a

White ash 0.896 0.094 0-341 2,459 O -442 10.123 bd IO-012 ab 10-045 ab *O-18lac 10,109 a

Values followed by the same letter. by colurnn. are not significantly different at ps0.05.

The estimated quantities of annual nutrients returned to the ground by Iitterfall of

different tree species are given in Table 3.3.

For al1 species, nutrient inputs within 1.0m to 2.0m from the tree row were

greater than the inputs at a distance of 6.0m to 7.0m except the nutrients of P. K.

Ca, Mg from silver maple. N: for walnut, this difference was 5.65 times, for red oak,

3.1 0 times, for silver maple, 2.92 times. for hybrid poplar. 2.04 times, for white ash.

12.73 times; P: for walnut, this difference was 5.80 times, for red oak, 3-21 times,

for hybrid poplar, 2.07 times, for white ash. 13.25 times; K: for walnut. this difference

was 5.76 times, for red oak, 3.1 5 times, for hybrid poplar, 2.07 times, for white ash.

12.39 times; Ca: for walnut, this difference was 5.65 times, for red oak, 3.16 times,

for hybrid poplar, 2.07 times, for white ash, 12.64 times; Mg: for walnut, this

difference was 5.76 times, for red oak, 3.17 times, for hybrid poplar, 2.07 tirnes. for

white ash, 12.00 times.

LittefiaIl frorn the trees in the intercropping system was a major contributor

of N but was also important as a source of nutrients taken up annually by plants,

e-g. Ca. Silver maple transferred the maximum N (1 5.2 kg-ha-') to the soil, followed

by hybrid poplar (1 1.0 kg-ha-'), white ash (4.86 kg-ha-'), red oak (4.62 kg-ha-'), black

walnut (1.74 kg-ha-'). Hybrid poplar transferred the most Ca (28.5 kg-ha-') followed

by silver maple (15.5 kg-ha-'), white ash (1 3.4 kgeha-'), red oak (1 1.1 kg-ha-'), and

black walnut (3.08 kg-ha-'). The magnesium content of Iitterfall ranged from 7.27

kg-ha-' for hybrid poplar to 2.37 kgaha-' for white ash. The potassium content of

litterfall ranged from 5.49 kg=ha-' for hybrid poplar to 0.50 kg-ha-' for black walnut.

40

Table 3.3. Estimated quantities of annual nutrients returned to the ground by litterfall of different tree species at different distances from the tree row in the intercropping systern.

Returned Black walnut Red oak Silver rnaple Hybrid poplar White ash nutrients (kg-ha- ) content mean conteniTëK content mean content mean' content mean

Values followed by the same letter by column across distances for the same nutrient element or by (row) across species are not significantly different at p i 0.05.

The phosphorus content of litterfall ranged from 1.06 kg9ha-l for hybrid poplar to

0.1 5 kg-ha" for black walnut (Table 3.3)-

The results from the intercropping situation can be compared to nutrient inputs

by Iitterfall under various forest types. The annual nutrient inputs by litterfall for N,

P. K. Ca and Mg were 34.0, 2.0, 16.0, 45.0 and 8.0 kg-ha", respectively in a

Quercus pinus (L.) forest (Henderson. 1977) and the annual nutrient inputs by

litterfall for N, NO,-N+NH,-N, K, Ca and Mg were 9.0. 1 -0. 8.0, 0.9 and 1 -4 kg-ha-'.

respectively, in an Eucalypt (Eucalyptus spp. Benth. & Hook.) plantation (Crockford,

1998). The nitrogen content of Iitterfall ranged from 41 kg-ha-' for an E. Regnans

forest (Ashton, 1975) to 9.8 kg-ha-' for an E. Obliqua/baxten (L' Herit.) forest (Lee

and Correll. 1 978). while the Ca of those forests were 48.8 kg-ha" for E. Regnans

and 17.1 kg-ha-' for E. Obliquahaxten. The inputs of phosphorus were 0.33 kgoha-'

and 1.9 kg-ha", respectively. Annual nitrogen inputs as high as 200 kg-ha-' have

also been reported by Nye (1971) for a moist tropical forest in Ghana with an

associated phosphorus input of 7.3 kg-ha". A comprehensive list of nutrient input

as litterfall by various forest types has been presented by Bevege (1 978). LitterfaIl

inputs under intercropping are lower than those in mature forest types. most likely

as a result of the lower tree density in the intercropped situation.

3.2 Throug hfall nutrient inputs

The average concentrations (mg-L-') of nutrients in the throughfall from different

tree species in the intercropping system and in rainfall are shown in Table 3.4.

42

Table 3.4. Average concentrations of various nutrients in the throughfall from different tree species in the intercropping system.

Concentrations of nutrients (mgC1 * SD) Species NOrN NH,-N P K Ca Mg Black walnut 0.6610.88 a 0.0810.17 a 0.68î1.48 a 5.3215.37 a 4.3613.08 a 1 Jïîl .O2 a

8 Red oak 1 ,09&1. 18 b 1.1713.38 b 0.7711.56 a 3.3712.75 a 3.9912.66 a 1.2310.65 b Silver maple l.8OIl.34 c 2.3418.79 c 0.4110.61 b 3.8611.83 a 4.8311.61 a 1.52kO.4Iab

hybrid poplar 1 XkO.88 bc 0.48k0.96 d 0.5111.25 b 7.9817.89 b 5.1211.70 b 1.57M.48ab

White ash 0,9510.88ab 0.2010.47a 0.4711.16b 3.4111.86a 4.5512,41a ll.42IQ.58ab

Values followed by the same letter by column across species are not significantly different at ps 0.05.

Silver rnaple exhibited the highest throughfall NO,-N and NHhN concentrations. For

KI Ca and Mg, throughfall concentrations aiways exceeded those in rainfall,

regardless of tree species. Little difference was noted between tree species.

although throughfall from hybrid poplar was higher than the other species for K and

Ca. Forthe N species and P, throughfall concentrations occasionally equalled those

found in rainfall. For example, P throughfall concentrations under black walnut and

red oak were higher than those found in rainfall, although throughfall P

concentrations under silver maple. hybrid poplar and white ash did not significantly

differ from those in rainfall-

Estirnated quantities of nutrients annually returned to the ground by net

throughfall from different tree species at the intercropping system are shown in

Table 3.5. Throughfall from the intercropped plantation canopy was a major

contributor of K and Ca. The net throughfall of hybrid poplar in the studied

intercropping field exhibited the maximum potassium inputs (1 5.44 kg-ha-'). followed

by silver maple (7.67 kg-ha.'), black walnut (2.99 kg-ha-'), white ash (1 -62 kg-ha-')

and red oak (1 -29 kg-ha-'). The calcium inputs of net throughfall ranged from 8.99

kg-ha-' for hybrid poplar followed by 8.93 for silver maple, to 1 -39 kg-ha" for red oak

and the net throug hfall of silver maple transferred the most NOrN and NH,Nl (2.73

and 3.05 kg-ha'' respectively), followed by hybrid poplar (1 -75 and 0.73 ), red oak

(0.24 and 0.34), white ash (0.32 and 0.10). black walnut (0.06 and 0.09). The

phosphorus inputs of net throughfall ranged from 0.38 kg-ha-' for hybrid poplar to

0.04 kg-ha-' for white ash and the magnesium content of net throughfall ranged

44

Table 3.5. Estimated quantities of nutrients annually returned to the ground by net throug hfall from different tree species at the intercropping system.

Nutrïents returned to ground (kg-ha-'-yr')

Species NO,-N NH,-N P K Ca Mg Black wainut 0-06 a 0-09 a 0-17 a 2-99 a 2.21 a 0.92 a

Red oak 0.24 b 0-34 b 0-14 a 1-29 a 1.39 a 0-42 a

Silver maple 2-73 c 3-05 c 0.12 a 7-67 b 8.93 b 2-77 b

Hybrid poplar 1.75 d 0-73 b 0.38 b 15.44 c 8.99 b 2-71 b

White ash 0-32 b 0-10 a 0-04 c 1-62 a 2.02 a 0.62 a -- - -

Net throughfall (kg-ha-') = throughfall (kg-ha-') - rainfall (kg-ha-'). Values followed by the same letter by column are not significantly different at ps 0.05.

from 2.77 kg-ha-' for silver maple to 0.42 kg-ha-' for red oak (Table 3.5). In short.

the silver maple and hybrid poplar, with the exception of P returns under silver

rnaple, retumed the highest nutrient contents of N, P. K, Ca and Mg from throughfall

to the surrounding intercropping system.

The results from the intercropping situation can be compared with nutrient

inputs from net throughfall under variouç forest types. The annual nutrient inputs by

throughfall for N. P. K. Ca and Mg were 2.9, 0.3, 16.7, 12.4 and 1.9 kg-ha-',

respectively in a Quercus prinus forest (Henderson, 1977). The annual nutrient

inputs in throughfall for N, NO,-N+NH,-N, K. Ca and Mg were 9.0. 1.0. 8.0, 0.9 and

1.4 kg-ha-'. respectively in an Eucalypt plantation (Crockford, 1998). and the annual

nutrient inputs in throughfall for N, P. K. Ca and Mg were 10.60, 0.63. 26.94. 6.98

and 1,98 kg-ha", respectively in a northern hardwood forest (Eaton. 1 973).

3.3 Sternflow nutrient inputs

The average concentrations (mg-L-') of nutrients in stemflow from different

tree species in the intercropping system and nutrient concentrations in rainfall are

shown in Table 3.6. For al1 nutrient elements, stemflow concentrations aiways

exceeded (ps 0.05) those in rainfall, regardless of tree species. Stemflow under

silver maple generally contained the highest concentrations of nitrate and

ammonium, with nitrate stemflow of silver maple = hybrid poplar whereas the

stemfiow under black walnut contained the highest concentrations of calcium and

magnesium. For phosphorus, stemflow concentrations under al1 five tree species

46

did not significantly differ from one another, although the concentrations were higher

than those found in rainfall. For magnesium. stemflow concentrations under four

tree species other than black walnut did not significantly differ from one another. For

P, K, Ca and Mg, respectively. stemflow concentrations from silver maple, hybrid

poplar and white ash were similar.

Estimated quantities of nutrients annually returned to the ground by net

sternflow from different tree species in the intercropping system are shown in Table

3.7. Stemflow from plantation canopies accounted for a very small proportion of

total nutrients added although P contributions were significant. The maximum

stemflow phosphorus flux was found associated with silver maple (4.10 kg-ha*'),

followed by 3.56 kg-ha-' for hybrïd poplar, 0.32 kg-ha-' for black walnut, 0.24 kg-ha-'

for white ash, and 0.13 kg-ha-' for red oak.

Except for NH,-N returns under hybrid poplar, al1 the nutrient elements,

NO,N, NH,-Nt Pl K, Ca and Mg fluxes under silver maple and hybrid poplar were

found to be higher than other tree species within the five studied tree species. The

NO,-N and NH,-N flux of net stemflow ranged from 0.05 and 1.20 kg-ha-',

respectively for silver maple to 0.01 and 0.004, respectively for black walnut. The

potassium flux of net stemflow ranged from 0.29 kg-ha-' for hybrid poplar to 0.08

kg-ha" for white ash, red oak and black walnut The calcium content of net stemflow

ranged from 0.1 2 kg-ha-' for silver maple to 0.04 kg-ha-' for white ash. The

magnesium content of net stemflow ranged from 0.05 kgoha-' for hybrid poplar to

Table 3.6. Nutrient concentrations in the stemflow from different tree species in the intercropping system.

Species NO,-N NH,-N P K Ca Mg (mg-L-' I SD)

Bfack walnut

Red oak

Silver maple

Hybrid poplar

White ash

Rainfall 0.51 0-08 0-45 0.22 O -60 0.21 10.56 d iO.12d k1.28 b 10-09 c 10-18 d 10.09 c

Values followed by the same letter by column are not significantly different at ps 0.05.

0.01 kg-ha-' for red oak and white ash. Except for hybrid poplar NH,-N, silver maple

and hybrid poplar retumed the highest NI P. K, Ca and Mg, respectively to the soi1

within the five studied tree species-

The results from the studied intercropping system can be compared with the

inputs of nutrients via net stemflow under various forest types. The annual nutrient

inputs by stemflow for N, K. Ca and Mg were 0.16. 2.22, 0.32 and 0.08 kgoha-'.

respectively in a red rnaple (Acer mbwm) plantation (Mahendrappa, 1974). The

annual nutrient inputs by stemflow for N, NO,-N + NH,-N. K. Ca and Mg were 0.6.

0.2, 1.5.0.2 and 0.3 kg-ha-', respectively in an eucalypt plantation (Crockford, 1998)

and the annual nutrient inputs by stemflow for N, P, K. Ca and Mg were 1.1 1, 0.1 0,

3.51. 0.64 and 0.19 kg-ha-'. respectively in a northern hardwood forest (Eaton.

1973).

3.4 Nutrient inputs and wheat growth response under tree rows

3.4.1 Nutrient inputs

As shown in the previous section, nutrient inputs from trees in an

intercropped situation rnay be substantial. The nutrients from throughfall and

sternflow will be imrnediately available to adjacent crop plants whereas the nutrients

in litterfaIl will only become available gradually, as the rate of release will depend

Table 3.7. Estimated quantities of nutrients annually returned to the ground by net stemfiow from different tree species in the intercropping systern-

Nutrients in stemflow returned to soi1 (kg-ha"-yf')

species NO,-N NH,-N P K Ca Mg BIack walnut 0-01 a 0-004a 0.32a 0-08 a 0.06 a 0-02 a

Red oak 0-01 a 0-01 a 0.13 a 0-08 a 0-05 a 0.01 a

Silver maple 0-05b 1.20b 4.10b 0.24b 0.12b 0.04b

Hybrid poplar 0-03 b 0.01 a 3-56 b 0.29 b 0.11 b 0-05 b

White ash 0.01 a 0.02 a 0.24 a 0.08 a 0-04 a 0.01 a

Net stemflow (kg-ha-') = Stemflow (kg-ha") - Rainfall (kg-ha-'). Values followed by the same letter by colurnn are not significantly different at ps 0.05.

on how rapidly litter leaches and decornposes For efficient and economic use of

fertilizers in intercropping systems, it is essential to understand the cycling of

nutrients in intercropping systems. The cycling of nutrients must be considered

when wheat or other crops and tirnber are removed from the intercropping system,

because it will influence prirnary productivity in the ecosystem.

A ) Annual nutrient inputs

Annual nutrient inputs (kg-ha-') by litterfall, throughfall and stemflow are

shown in Table 3.8. Litterfall, on average, represented 90.5% al1 nitrogen inputs

from the tree vegetation while throughfall and stemflow accounted for 8.9% and

0.6%. respectively. Throughfall, on average. represented 62.7% al1 potassium

inputs while litterfall and stemflow accounted for 35.6% and 1.7%. respectively.

Stemflow. on average. represented 50.3% al1 phosphorus inputs while litterfall and

throug hfall accounted for 37.0% and 1 2.7%,respectively. Litterfall from the

plantation canopy was the major contributor of N, wher-as for some species (e-g.

hybrid poplar, silver maple) throughfall contributed the most K. Stemflow accounted

a very small proportion of the nutrients received at the soi1 surface, but in certain

species (e-g. silver maple, hybrid poplar) contributed the most P. K inputs from net

throughfall comprised 83.7% of the total nutrient input for black walnut, followed by

72.8% for hybrid poplar to 39.9% for red oak. P inputs from net stemfiow comprised

78.6% of the total nutrient input for silver maple, followed by 71 -2% for hybrid

poplar to 20.5% for red oak.

Table 3.8. Annual nutnent inputs ( kg-ha-') by Iitterfall, net throughfall and net sternflow, and associated percentages-

Total-N NO,-N NH,-N P K Ca Mg Black walnut Litterfall 1-74 0-15 0-50 3 -08 3-21 Net throughfall 0-06 0-09 O. 175 2-99 2.21 0-92 Net sternflow 0-01 0.004 0.32 0-08 0.06 0-02 Total 1 -74 0-07 0-1 O 0.63 3-57 5-35 4.16

LitterfaIl 23.7% 14-0% 57.6% 77.3% Net throughfall 3,6% 53% 26.0% 83,7% 41.3% 222% Net stemfiow 0,37% O-21% 50.3% 2.30% 1-10% OSO?! Red oak Litterfa t l 4.6 0.35 1-87 1 1-09 3-29 Net throughfall 0.24 0.34 0-14 1-37 1-39 0-42 Net stemflow 0-01 0-01 0-13 0 -08 0-05 0-01 Total 4.6 0.25 0-35 0-62 3-25 12.53 3-73

Litterfa Il 56.8% 57.6% 885% 88.3% Net throughfall 5.1% 7.3% 22.7% 39.9% 11-1% 11.3% Net stemflow 0.17% - 0.26% 20.50% 0.25% O-40% 0-40% Silver maple LitterfaIl 15.22 0.99 3.13 15.51 2.50 Net throughfall 2-73 3.05 0-1 2 7.67 8.93 2-77 Net stemflow 0.05 1 -20 4.10 0-24 0.12 0.04 Total 15-22 2.78 4.25 5.21 1 1.04 24.56 5-31

LitterfaIl 19.0% 28.4% 63.2% 47.1% Net throughfall 17-9% 2OcO3/o 2.4% 69.5% 36.4% 522% Net stemflow 0.31% 7.9% 78.6% 2-1% 0,4% 0,7% Hybrid poplar litterfall 10.99 1 .O6 5.49 28.51 7.27 Net throughfall 1.75 0.73 0.38 15.44 8-99 2-77 Net stemf ow 0.03 0.07 3.56 0-29 0.1 1 0.05 Total 10.99 1.78 0-74 4.99 21 -22 37.61 10-03

LitterfaII 21.2% 2Sc9% 75.8% 725% Net throughfall 15.9% 6.6% 7.5% 72.8% 23.9% 27.1%

0.29% O-07% 71.2% 1,3% 0.30% 0.47% Net stemflow White ash LitterfaIl 4-88 0.51 1 -84 13.38 2.37 Net throughfall 0.32 0.10 0.048 1-63 2-02 0.62 Net stemfiow 0.01 0.002 0.24 0.08 0-04 0.01 Total 4.88 0.33 0-1 1 0.79 3-55 1 5.44 3-01

LitterfaIl 64.5% 51.8% 86_66% 7874Dh Net throughfall 6-6% 2.2% 4.8% 459% 1 3-1% 20206?! Net sternfiow 0.15% 0.03% 30.7% 2.3% 0.28% O.Wh

2) Soil nitrogen

Cornparisons of nitrogen concentrations (% dry weight. pg-100g-'SD) in the

0-20cm soi1 layer at different distances frorn tree rows under different tree species

at the intercropping system are shown in Table 3.9. Total N concentrations (% dry

weight), at distances of 1,0m, 3-5m and 6.0m from the tree row, were not

significantly different under any tree species, whereas total N concentrations within

tree species at a distances of 1 -Orn and 3.5m from tree row were significantly

different. There was no significant difference in soi1 NO,-N or NH,-N within species

across the three distances. NO,-N concentrations in the soi1 (pg-100g") at the

distances of 1.0m from tree row were significantly different from those at a distance

of 6.0m for black walnut, red oak, silver maple and hybrid poplar but not white ash.

There was no significant difference of NH4-N concentrations within 1.0m, 3.5m and

6.0m from tree row for the most tree species although the NH,-N concentrations of

hybrid poplar at the distance of 1.0m from tree row was different from that at a

distance of 6.0m.

Seasonal sampling (June, July, August) of soi1 NO,-N and NH4-N indicated

that the highest soi1 NOzN concentrations were found in July. The highest soi1 NH,

N concentrations were found at the beginning of the sarnpling season in June.

Estimated quantities of soi1 nitrogen content (kg-ha-') in the 0-20 cm soi1

layer at different distances from tree rows under different tree species at the

intercropping system are shown in Table 3.1 0. Soil total N ranged from 41 06 kgeha-'

for silver maple at a distance of 3.5m from tree row to 3043 kg-ha" for red oak at a

53

Table 3.9. Cornparison of nitrogen concentrations in the 0-20 cm soi1 layer at different distances from tree rows under different tree species at the intercropping system.

Soil nitrogen concentrations by different distances from tree row Species 1,Om 3.5m 6,Om

TN NO3-N NH4-N TN NO3-N NH4-N TN NO34 NHA-N (W (pg'100") (%) (~g*loO'l) (%) (C(g*IOO")

Black walnut 0,14 a 1392.53 a 232,49 a 0,14 a 856,16 a 122,81 a 0,14 a 532,43 a 209,33 a ~1 f0,002(a) &604,75(a) k l 71 .85(a) 10.02(a) &718,86(a) 1137.88(a) 10.02(a) 1514,81 (b) 1323,48(a) A

Red oak 0,13 ab 1235,47 a 333,19 a 0,13 a 998,47 a 155,81 a 0.13 a 552,47 a 162.21 a 10.01 (a) 1547.49(a) *358,58(a) 10.09(a) 1662.90(a) 11 gO.ig(a) 10.01 (a) t311,77(b) 11 48,94(a)

Sîlver maple 0,16 a 1203.46 a 287,55 a 0.17 b 722,06 a 299.95 a 0,14 a 433,Ol a 224,66 a 10.02 (a) 161 8.25(a) 11 74,66(a) tO.O1 (a) 1387,33(a) 1256.66(a) 10,05(a) t215,94(b) f 172.61 (a)

Hybrid poplar 0.16 a 97661 a 331,59 a 0,17 b 523.59 a 194,83 a 0,16 a 370,89 a 145,51 a 10.02 (a) k608.94(a) +l56,83(a) tO.O1 (a) 1444.51 (a) 11 3l,54(a) +0.01 (a) 11 57.99(b) 1145,32(b)

White ash 0,17 ac 1016.69 a 238,48 a 0.168 b 61564 a 183.10 a 0.16 a 509,02 a 306,52 a 10.01 (a) î655.27(a) +lOl.65(a) 10,02(a) f503.82(a) f l36,24(a) 10,02(a) 1337,12(a) 11 78,24(a)

- - - -- -- -

Values followed by the same letter or letter pairs by column across species, or by (row) across distance for the same nutrient element are not significantly different at ps; 0,05,

Table 3.1 0. Estimated quantities of soi1 nitrogen content (kg-ha-') in the 0-20 cm soi1 layer at different distances from tree rows under different tree species in the intercropping system.

Nitrogen content by different distances from tree row Species 1.0m 3.5m 6,Om

TN NO3-N NH4-N TN NO3-N NHA-N TN NOrN NHcN (kg~ha'')

Black watnut 3432.0 a 33.4 a 5.6 a 3271.2 a 20.6 a 2.9 a 3250,O a 12.8 a 5.0 a

Red oak 3225.6 ab 29.7 a 8,O a 3163.2 a 24.0 a 3.7 a 3043,2 a 13.3 a 9,9 a (a) (a) (a) (a) (a) (a) (a) (b) (a)

Silver maple 3921.6 a 28.9 a 6.9 a 4106.4 b 17.3 a 7.2 a 3408.0 a 10.4 a 5.4 a (a) (a) (a) (a) (a) (a) (a) (b) (a)

Hybrid poplar 3876.0 a 23.4 a 8.0 a 4070.4 b 12.6 a 4.7 a 3868.8 a 8.9 a 3.5 a (a) (a) (a) (a) (a) (a) (a) (b) (b)

Values followed by the saine letter or letter pairs by column across species, or by (row) across distance for the same nutrient element are not significantly different at ps 0.05.

distance of 6.0rn. Soif NH,-N ranged frorn 9.89 kg-ha-' for red oak at a distance of

6.0m to 2.95 kg-ha-' for black walnut at a distance of 3.5m. Soi1 NO,-N within 1 -0rn

of the tree row for black walnut were 2-62 times the content at a distance of 6.0m;

for red oak, 2.24 times; for silver maple, 2.78 times; for hybrid poplar, 2.63 times.

3.4.2 Wheat growth response

1) Wheat tillers

The average annual number of wheat tillers per plant (tillers-plant-') by

different distances frorn tree rows under different tree species at the intercropping

system are shown in Table 3.1 1. The number of wheat tillers per plant by distances

of 1.0m. 3.5m and 6.0m from the tree rows. across the five species ranged frorn 5.8

tillers*plant-' for white ash at a distance of 1.0m from tree row in 1997 to 2.0

tillers-plant-' for black walnut at a distance of 6.Om in 1998. Wheat tillers per plant

within 1.0m of the tree row for black walnut were 1.57 and 1.75 times (in 1997 and

1998 respectively) those at a distance of 6.0m; for red oak, 1.33 in 1997 only; for

silver maple. 1.33 times (1998 only); for hybrid poplar, not significant and for white

ash. 1.66 and 1.42 times. The average nurnber of wheat tillers per plant at any

distance in both 1997 and 1998 were not affected by the presence of any particular

tree species-no sig nificant differences existed.

2) Wheat biomass

The average accumulated wheat biomass (kg-ha-') by different distances

56

Table 3.1 1. Wheat growth response (tillers-plant-') at different distances from tree rows under different tree species in the intercropping system-

(tillers-plant-'Hl) by distances from tree rows S pecies 1997 1998

1 -0m 3-5m 6 -0m 1 -0rn 3-5m 6-Om Black walnut 4.7 a 3-5 a 3-0 ab 3-5 a 2-8 a 2-0 a

10.2(a) 10.3(b) &0.7(bc) i0.7(a) *O-4(ab) 10.5(b)

Red oak 4-4 a 3-8 a 3-3 a 2-9 a 2-2 a 2-3 a îO_4(a) *O-3(a) &0.3(bc) *0,5(a) I0S(a) *0.7(a)

Silver maple - - - 3.2 a 2.6 a 2-4 a *0_3(a) *O .2(b) IO. 1 (b)

Hybrid poplar 4.5 a 4.2 a 3.9 ac 3.5 a 2.6 a 2.5 a *0.5(a) *O -7(a) &O 3(a) 11 4(a) Ii0-6(a) *0.4(a)

White ash 5-8 a 3.6 a 3 - 5 a 3-7 a 3.3 a 2-6 a 11.3(a) 10-5(b) *0.6(bc) *0.6(a) &0.7(ab) i0.4(b)

Values followed by the same letters or letter pairs by ( row) across distance or by column across species are not significantly different at ps 0.05.

from the tree rows under different tree species are shown in Table 3.12. The mean

of 1997 and 1998 of annual wheat biomass (kg-ha-') by distances of 1 .Omr 3.5m.

6.0m from tree rows, across the tree species ranged from 9833 kg-ha-' for white ash

at a distance of 1 .Om to 5038 kg-ha-' for black walnut at the distance of 6.0m from

tree row. Significant differences were found across distances in both 1997 and

1998. For the species comparÏson, significant differences in wheat biomass existed

only between red oak and white ash at a distance of 1 .Om in 1997. The average

annual wheat biornass under black walnut within 1 .Om of the tree row was 1.69 and

2.01 times, for 1997 and 1998 respectively the annual wheat biomass at a distance

of 6.Om; for red oak, 1.36 and 1.82 times; for silver maple. 2.23 times (1998 only);

for hybrid poplar. 1.45 times (1 998 only); and for white ash, 1.49 and 1.49 times-

The two year mean, with al1 distances combined, ranged from 7748 kg-ha-' for white

ash to 6545 kgoha-' for red oak.

3) Wheat yields

The average annual wheat yields (kg-ha-') by different distances from tree

rows under different tree species at the intercropping system are shown in Table

3.1 3. The wheat yields were significantly different between the distance of 1.0 m

and 6.0m from the tree rows. Wheat yield ranged from 5046 kg-ha'' for white ash

at a distance of 1.0m from tree row in 1997 to 1800 kgha-' for black walnut at a

distance of 3.5m in 1998. Wheat yields within 1.0m of the tree row for black walnut

were 1.71 and 2.32 (in 1997 and 1998 respectively) those at a distance of 6.Om; for

Table 3.12. Wheat biomass (kg-ha-') at different distances from tree rows under different tree species in the intercropping system-

Annual wheat biornass (kg-ha-'SD) by distances from tree rows Species 1997 1998

1-Om 3.5m 6.0m 1 ,Om 3-5m 6-0m Mean Blackwalnut 9400 a 7300 a 5550 a 9100 a 4330 a 4525 a 6701

e21(a) 1154(ab) 1161(b) 181 (a) i 4 1 (b) 163(b)

Red oak 7400ab 7450a 5450a 8980a 5055a 4935a 6545 *15l(a) i45(a) ~ l O l ( b ) i76(a) i 81 (b ) 1114(b)

Siiver maple - - - 9545 a 5795 a 4710 a 6683 11 33(a) 11 O8(b) 11 26(b)

Hybrid poplar 8450 a 8100 a 7200 a 8580 a 5360 a 5915 a 7268 *154(a) i209(a) 133(a) &%(ab *93(b) 130(b)

White ash 17700ac 7750a 7850a 7965a 5880a 5340a 7748 i215 (a) t149(b) I 2 8 (b) 11 75(a) i62 (ab) 11 O8(b)

Values followed by the same letters or letter pairs by (iow) across distance within years or by column across species are not significantly different at ps0.05.

red oak, 1.45 and 1.97 times; for silver maple, 1.90 tïmes (1 998 only); for hybrid

poplar. 1.49 times (1 998 only) and for white ash, 1.54 and 1.52 times. Wheat yiekls

at any distance in 1998 were not significantly different between tree species. In

1 997, some minor differences in wheat yield were noticed between the white ash

and other treatments but only at tom; no differences were noticed at other

distances. The two year mean, with al1 distances combined, ranged from 3394

kg-ha-' for white ash to 2858 kg-ha-' for red oak.

The winter wheat grain yields in the intercropping system and in an

monocropping system were estimated using data from this study. Assuming that the

distance between tree rows is 15m and that the yield of the centre plot (a distance

of 6.0m - 9.0m from one side of tree row) is equivalent to the yield found in a

monocropping system, the yields in the intercropping and monocropping situations

were 2450.3 kg-ha" and 2244.4 kgoha-' respectively. There was a 8.4% yield

increase in the intercropping system compared to the monocropping system-

Excluding land occupied by the tree rows, these yields are equivalent to those found

on adjacent monocropped fields-

4) Wheat grain total nitrogen

Average concentrations of wheat grain total N (% dry weight) by different

distances from tree rows under different tree species at the intercropping system

are shown in Table 3.14. There was no significant difference among the wheat grain

TN concentrations within the five studied tree species, across the three distances

Table 3.1 3. Wheat yield (kg-ha-') at different distances from tree rows under different tree species in the intercropping system.

Annual wheat yield (kgoha-'k SD) by distances from tree rows

S pecies

Black walnut 41 36 ab 2991 a 2421 a 4351 a 1800 a 1877 a 2929 1127(a) 152 (ab) 157 (b) d24 (a) i27 (b) G!9 (b)

Red oak 3309a 3237a 2287a 4053a 2200a 2062a 2858 fil (a) I 2 7 (a) 149 (b) *29 (a) 145 (b) 152 (b)

Silver maple - - - 4516 a 2722 a 2375 a 3204 179 (a) 160 (b) k61 (b)

Hybrid poplar 3086 a 3357 a 2923 a 3726 a 2128 a 2495 a 2953 172 (a) 6 7 (a) 115 (a) 141 (a) 164 (b) k12 (b)

White ash 5046b 3339a 3282a 3643a 2643a 2413a 3394 188 (a) 164 (b) il 18(b) 166 (a) 134 (b) 151 (b)

Values followed by the same letters or letter pairs by ( row) across distance within years or column across species are not significantly different at ps0.05.

Table 3.14. Average total nitrogen concentrations of wheat grain (% dry weight) at different distances from tree rows under different tree species in the intercropping system-

Wheat grain TN (% dry weig ht f SD) by distances from tree rows Species 1 -0m 3-5m 6.0m Black walnut 1-91k0-28 a (a) 1,7810.12 a (a) 1.9110-21 a (a)

Red oak 1 -68k0.15 a (a) 1-71f0.11 a (a) 1 -8810.05 a (b)

Silver maple 1 -94k0.25 a (a) 1.81k0-18 a (a) 1.941021 a (a)

Hybrid poplar 1 -68I0.08 a (a) 1-77k0.11 a (a) 1-75I0.13 a (a)

White ash 1 -76*0-20 a (a) 1 -7910-1 4 a (a) 1 -89*0- 1 0 a (a)

Values followed by the same letten by column across species. or by (row) across distance are not significantly different at ps 0.05,

of 1.0m. 3.5m and 6.0m. Signifiant difference among grain TN concentrations were

only found in the red oak treatment. where wheat grain TN at 6.0m from the tree

row was significantly higher than at either 1.0m and 3.5m.

Estimated quantities of wheat grain total N content (kg-ha-') by different

distances from tree rows under different tree species at the intercropping system

are shown in Table 3.15. Annual wheat grain total N

distances of 1 .Om, 3.5m and 6-0m from the tree rows,

content (kg-ha-'-yr') by

across the five species

ranged from 87.79 kg-ha" for silver maple at a distance of 1 -0m from tree row to

31 -80 kg-ha-' for black walnut at a distance of 3.5~1. Wheat grain total N content

within I.Om of the tree row for black walnut were 2-34 times the content at a

distance of 6.0m; for red oak, 1.75 times; for silver maple, 1.93 times; for hybrid

poplar, 1.43 times and for white ash. 1 -42 times. An average 51 -99 kg TN per

hectare was removed annually from wheat grain harvest at the studied field with the

five tree species.

The above results indicate that the trees in the studied intercropping system

provided additional nutrients to adjacent crops. Winter wheat, which is planted in

the previous fall and grows mostly in the spring before the tree leaves flush out,

benefts from tree nutrient inputs. Wheat apparently does not compete with trees for

Sun light and fully uses the fertilizer inputs from the trees.

5) Implications and recommendations

63

Table 3.1 5. Estimated total nitrogen contents of wheat grain (kg-ha") at different distances from tree rows under different tree species in the intercropping systern in 1998-

Wheat grain TN content (kg-ha-') by distances from trees

Species 1 -0m 35m 6-0m

Black walnut 83-56 a (a) 31 -80 ab (b) 35.78 a (b)

Red oak 67.86 a (a) 38-04 a (b) 38-72 a (b)

Silver maple 87-79 a (a) 49-22 ac (b) 45-41 a (b)

Hybrid poplar 62-75 a (a) 37.26 a (b) 43.80 a (b)

White ash 65.02 a (a) 47.21 a (a) 45-70 a (a) Values followed by the sarne letten or letter pairs by ( row) across distance or by column across species are not significantly different at p i 0.05.

Greater amounts of cations, especially potassium, were found in throug hfall

compared to litterfall and stemflow presurnably because the cations in foliage were

available for leaching. However. nitrogen and phosphorus were less available for

leaching due to translocation from the foliage and because they primarily present

in organically-bound forms.

While the nutrient fiuxes of Iitterfall, net throughfall and net sternflow varied

among tree species, no correlation were found between these parameters and

wheat yield and biomass and soi1 nitrogen content. This is rnost likely because of

difierences in decomposition rates of foliage and accumulation processes. The

foliage of silver maple and hybrid poplar decomposes faster than red oak, black

walnut or white ash. Leaves of red oak, for example. contain more lignin which

takes a longer time to breakdown. The compound ieaves of black walnut and white

ash are arched which allow individual leaflets to rest off the ground, making them

harder to decay. In addition, the trees at the study site are 13 years old and It is

difficult to interpret the history of nutrient accumulation that has occured over the

period of the study. More research is necessary to further explain the results.

The total nitrogen content of wheat grain ai l m from the tree rows was 20 to

49 kg-ha-' more than that of wheat grain at a distance of 6m. The additional nitrogen

came not only from the nutrient inputs of litterfall. throughfall and stemflow but also

from decomposing fine tree roots.

The results indicate that farmers could consider growing wheat next to tree

rows. Farmers may either fertilize more in the middle of the alley between the tree

65

rows to increase the yield in that area or reduce fertilization close to the tree rows

to lower costs-

4- CONCLUSIONS

The annual nutrient inputs from tree vegetation are a significant contributor

to nutrient availabilit. in a intercropping system.

The average annual nutrient inputs by litteifall for N, P, K. Ca and Mg were

7.49, 0.61, 2.57, 14.31 and 3.24 kg-ha-'-yrt. respectively (Ca > N > Mg > K > P).

The average annual nutrient input by net throughfall for NO,-N, NH,-NI P. K. Ca and

Mg were 1.02, 0.86. 0.17. 5.81. 4.71 and 1.49 kg-ha4-yfl, respectively (K >Ca >

NO3-N+NO,-N > Mg >P). The average annual nutrient inputs by net stemflow for

NO3-N, NH,-NI P. K. Ca and Mg were 0.014, 0.25, 1.62, 0.15. 0.08, and 0.03

kg-ha-'-yr', respectively (P > NO3-N+NO,-N >K > Ca > Mg). Litterfall, on average.

represented 90.5% al1 nitrogen inputs from the tree vegetation while throughfall and

stemflow accounted for 8-9% and 0.6%, respectively. Throughfall, on average,

represented 62.7% al1 potassium inputs while litterfall and stemflow accounted for

35.6% and 1.7%. respectively. Stemflow, on average. represented 50.3% al1

p hosp horus inputs while litterfall and throughfall accounted for 37.0% and

12.7%,respectively. Litterfall from the plantation canopy was the major contributor

of NI whereas throughfall contributed the most K and stemflow accounted for a very

small proportion of the nutrients but contributed the most P.

The average annual total-N input by litterfall for silver maple, hybrid poplar.

white ash, red oak and black walnut were 15-22. 1 0.99.4.88.4.62 and 1.74 kg-ha-'.

respectively. The average annual P inputs by Iitterfall. net throughfall and net

stemfiow for silver maple, hybrid poplar, white ash, black walnut and red oak were

5.21.4.99 0.79. 0.63 and 0.62 kg-ha-'. respectively. The average annual K inputs

by litterfall, net throughfall and net stemflow for hybrid poplar, silver maple. black

walnut, white ash and red oak were 21 -22. 11 -04. 3.57. 3.55 and 3.25 kg-ha-'.

respectively .

Inputs of N from tree vegetation result in increased soil inorganic N during the

growing season. The average soi1 inorganic N content within 1.0m of the tree row

was 2.1 0 times the soi1 inorganic N content at a distance of 6.0rn. The average

annual wheat grain total N content at 1 -0rn of the tree row was 1 -75 tirnes the grain

total N content at a distance of 6.0m, and the average annual wheat yield at 1.0m

of the tree row was 1.60 times the wheat yield a i a distance of 6.0m.

The study demonstrates that wheat grown adjacent to tree rows benefits from

the additional nutrients contributed by litterfall, throughfall and stemflow. Among the

five tree species in the studied intercropping system, silver maple and hybrid poplar

were the best species in terms of nutrient input.

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6. APPENDICES

Appendix 1. Seasonal patterns of throughfal1 for various nutrients in an

intercropping system in Southern Ontario, Canada 1997-1 998.

Appendix 2. Seasonal patterns of stemfiow for various nutrients in an

intercropping system in Southern Ontario, Canada 1997-1 998.

Appendix 3. Modelling nutrient inputs in an intercropping situation in Southern

Ontario, Canada-

Appendix 1. Seasonal patterns of throughfall for various nutrients in an

intercropping system in Southern Ontario, Canada 1997-1998- .

Figure 6.3 through 6.3 show the seasonal pattens of phosphoms, nitrate and

ammonium fluxes in throughfall under different tree species. The nutrient fluxes

from event to event varied strongly (pc0.05) for al1 three elements.

The values of 0-20 on figure 6.1,6.2 and 6.3 represent the dates which are:

1-July 15, 1997 2-July 21, 1997 3-J~ ly 28, 1997 4- AU^. 14, 1997

5Aug. 16. 1997 6-Aug. 21, 1997 7Aug. 28, 1997 8-Sept. 7, 1997

9-Sept. 1 1, 1 997 10-sept. 20. 1997 1 1 -Sept. 26, 1 997 12-0ct.24. 1997

13-oct. 29, 1997 1CNov. 4. 1997 15-May 31,1998 16-June 3,1998

17-June 12,1998 18-June 17,1998 19-June 24,1998 20-June 30,1998

- - ranfal -+ - walnut ' - oak maple ::

-poplar -*-ash l

I

Date

Figure 6.1. Temporal changes in phosphorus fluxes in throughfall passing through the vanous tree species at the intercropping system.

--.--- rainfall - - walnut

oak - e- maple --- poplar - -0 - ash

O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Date

Figure 6.2- Temporal changes in nitrate fluxes in throughfall passing through various tree species at the intercropping system

84

1 --*-- rainfaii - wainut I

- oak -=- maple / \ -+ poplar -- - ash

O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Date

Figure 6.3. Temporal changes in ammonium fluxes in throug hfall passing through vanous tree species at the intercropping system

Appendix 2. Seasonal patterns of stemflow for various nutrients in an

intercropping system in Southern Ontario, Canada 1997-1 998.

Figure 6.4 through 6.6 show the seasonal pattens of nutrient fluxes of

p hosp horus, nitrate and ammonium from stemflow under different tree species. The

nutrient Ruxes from event to event varied strongly (Pc0.05) for al1 three elements.

The significant differences (pç0.05) were presented in stemflow fluxes across tree

species-

The values of 0-20 on figure 6.4, 6.5 and 6.6 represent the dates which are:

1-JUIY 15, 1997 2-JUIY 21. 1997 3-July 28, 1997 4- AU^. 14, 1997

5-Aug. 16, 1997 6-Aug. 21, 1997 7Aug. 28, 1997 8-Sept 7, 1997

9-Sept.11, 1997 10-sept 20, 1997 1 1 -Sept. 26, 1997 12-0ct. 24, 1997

13-oct. 29,1997 14-NOV. 4, 1997 15-May 31,1998 16-June 3,1998

17-June 12,1998 18-June 17,1998 19-June 24,7998 20-June 30, 1998

. walnut oak maple p o p l a r

-.,- ash

O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 f 18 19 20

Oate

Figure 6.4- Temporal changes in phosphorus fluxes in stemflow under various tree species a t the intercropping system

- , . walnut oak maple poplar

-..-. ash

Date

Figure 6.5. Temporal changes in nitrate fluxes in stemflow under various tree species at the intercropping systern

-., . - walnut oak a

C 0-1 - , . maple - poplar QI -..-- ash

Date

Figure 6.6. Temporal changes in ammonium fluxes in stemflow under various tree species at the intercropping system

Appendix 3. Modelling nutent inputs in an intercropping situation in Southern Ontario, Canada-

Comparison of Soil Organic Matter compononts in an Intercropping System and a Monocropping System Using the CENTURY Model

ABSTRACT

This study compares the SOM regime (dynamics of SOM residue, SOM

carbon, SOM nitrogen) in intercropping and monocropping systems using the

CENTURY mode1 as an evaluation tool. The results show that the SOM residue in

an intercropping system is 4 times the amount in a monocropping system; SOM C

in an intercropping system is 2 times the amount in a mûnocropping system. Total

N input in an intercropping systern is also more than monocropping system, while

mineral N leaching in stream flow is lower.

Key Words: lntercropping system. monocropping system. SOM residue. SOM

carbon, SOM nitrogen

INTRODUCTION AND LITERATURE REVIEW

Soil organic matter (SOM) plays an important role in nutrient cycling and soi1

productivity in al1 ecosystems. SOM is a major agent that stabilizes aggregates and

can be adequately described by three different p o o k an active pool (microbial

biomass), a slow pool and a passive pool. The amount and stability of soi1 organic

matter depends on how much organic matter entes the soil each year and how fast

this organic matter decomposes in the soil (Parton et al., 1987: Voroney et al.,

1995). Decomposition, turnover and the biochemistry of soi1 organic matter are

affected by different cropping systems. lntercropping is considered an excellent

land-use system because of its productivity, sustainability and adoptability (Nair,

1993; Williams and Gordon, 1997). The purpose of this study was to compare soi1

organic matter between intercmpping practices and monocropping practices, using

the CENTURY rnodel.

The CENTURY mode1 developed by Parton et al. (1 987) has been used to

analyse the short-term effects of management on soi1 organic rnatter in Quebec,

Canada, and to sirnulate management practices, crop production and soi1 organic

matter dynamics at each field site (Voroney et al. 1995). The CENTURY model can

simulate the impacts of climate and farm management effects on prirnary

productivity, C, N, P. and S dynamics and soi1 water balance in agroecosysterns.

al1 of which centre around soi1 organic matter dynamics (Parton et al., 1983, 1987,

1988; Paustian et al., 1992; Carter et al., 1993; Probert et al., 1995; Vallis et al.,

1996). The CENTURY model has also been used to evaluate the impact of

alternative farrn management practices on nitrogen pollution of ground water in

southwestern Ontario. It can be used to gain insights into the effect of fertilizer

management, tillage treatment, crop choice, and multi-crop rotation effects on N

90

leaching and on crop yields (Yiridoe et al., 1997) and has been used to analyse the

interactions between organic matter addition, fertilization, and crop productivity

(Paustian et al., 1992).

MATERIALS AND METHODS

Study Site

The field site was located at Agroforestry Research Station. University of

Guelph, in southern Ontario (43' 32' 28" N, 80 92' 3 2 W). Mean annuai

precipitation at the site is 836mm yr' and the mean annual temperature is 6.65 OC.

The soi1 is a sandy clay loam with a clay content of 35% (Brunisolic Gray Brown

Luvisol).

The site had been used for continuous production of hay prior to initiating

the intercropping study in 1987. Annual crop production had been declining and soi1

erosion was becorning serious. Since 1987, trees (mostly broad leaf tree species)

have been planted into this site with row spacing of 12.5m or 15m between crops;

three crops have been grown on the site using a corn - soybean - winter wheat

rotation.

Treatment and Management Description

The treatments of this study were: (1) monocropping - continuous hay

production was simulated over 20 years from 1965 to 1985, then the rotations of

91

corn-soybean- winter wheat were simulated over 30 years from 1986 to 201 5.

(ii) intercropping - continuous bariey production were simulated over 20 years from

1965 to 1985, then the intercropped, broad leaf trees and the rotations of corn-

soybean- winter wheat. were simulated over 30 years from 1986 to 2015. To be

constant. the growing season for al1 crops and trees was detemined to be from

April to September, and 50% straw from crops was removed from study site every

year. 100% of the deciduous tree leaves fall at the end of the growing season.

Fertilization (medium) and cultivation (plow) were carried out once a year,

respectively, in each of the 50 simulation years.

The CENTURY model

The CENTURY model is a general model that has been used extensively to

describe the SOM dynamics for different ecosystems. The CENTURY mode!

enables the user to simulate several different land uses and allow for a wide variety

of management options (Motavalli et al. 1994). The model is used for predicting site

productivity and soi1 dynamics over periods in excess of those available for field

experimentation. Results have shown that the modei accurately simulated total soi1

organic carbon, nitrogen dynarnics, and net primary productivity (NPP) across a

wide range of managed and natural tropical ecosysterns (Parton et al. 1994).

The model is broken down into three soi1 organic pools (active, slow and

passive), which have different associated below and aboveground Iitter pools,

decornposition rates and a surface microbial pool which is associated with

92

decomposing surface Iitter (Metherell et al. 1 993).

In the execution process of the CENTURY 4.0 model there are 5 main

stages:

1. File1 00 - User inputs the data for their specific site

2. Eventl00 - User plans the events to occur over time

3. CENTURY execution

4. List1 00 - User identifies variables for output

5. Reading output - User exports data to graphical software (e-g., Excel)

Parameterization

The CENTURY model functions on a rnonthly time-step that requires:

-monthly average max and min air temperature

-monthly precipitation

-soi1 texture

-plant nitrogen, phosphoros, and sulfur

-1ignin content of plant material

-atrnospheric and soi1 nitrogen inputs

-initial soi1 carbon, nitrogen, phosphoros and sulfur

Wherever information was unavailable, the data from the Elora research

station, 15 km away from the study site was used to fiIl the gaps.

Site-specific parameters, crop parameters and initial conditions such as soi1

93

texture, bulk density, soi1 depth, pH, total soi1 C and N content, initial mineral values,

monthly precipitation and mean maximum and minimum monthly temperature were

obtained from the field site at EIora Research Station, University of Guelph in

southern Ontario. Tree parameters are based on fked values that are set in the

Tree. 1 00 file-

RESULTS AND DISCUSSION

The different cropping systems (intercropping and monocropping) resulted

in changes to soi1 organic matter residue, soi1 organic matter carbon and soi1

organic nitrogen using the CENTURY model.

Soil Organic Matter Residue Dynamics

SOM residue dynamic is a useful indicator for turnover of organic matter in

both intercropped and monocropped soil. The SOM residue in the surface of the

intercropping system stays at 450 kg ha-' from 1 990 to 201 5. Meanwhile, it is 250

kg ha-' in the monocropping system. The SOM residue in the soi1 of the

intercropping system keeps increasing from 1987 to 2015 and amounts to 2.5 t ha-'

in 2015. In monocropping system, it is 0.6 t ha". The SOM residue in soi1 in the

intercropping system is 4 times the amount of the monocropping system.

Soil Organic Matter Carbon Dynamics

94

Table 6.1. Carbon pools and fluxes in intercropping and monocropping systems.

Carbon parameters lntercropping Monocropping

annual C input 1-5 t ha-' 0-8 t ha-'

litter structural C in surface 280 kg ha-' 120 kg ha-'

litter structural C in soi1 2-5 t ha-' 0-5 t ha"

C in active SOM in surface 120 kg ha-' 27 kg ha-'

total C including belowground 45 t ha-' 32 t ha''

surn of C in wood components 4.7 t ha-' O t ha-'

total C in forest sysiem 70 t ha-' 35 t ha"

C from organic leaching of stream flow 0.2 kg ha-' 0.1 kg ha-'

annual CO, respiration 1 -7 kg ha" yr -' 1.0 kg ha-' yr -' annual accumulator for CO, loss 300 kg ha-' yr -' 200 kg ha-' yr -'

Table 6.2. Ntrogen pools and fluxes in intercropping and monocropping systems.

Nitrogen parameters lntercropping Monocropping

total N 4 t ha-' 3.8 t ha"

litter structural N 1.4 kg ha-' 0.5 kg ha-'

N in active SOM 8 kg ha-' 2.2 kg ha-'

N from mineral leaching of strearn flow O g ha-' 1.5 g ha-'

SOM carbon is the main component of SOM. SOM carbon dynamics

represent the biological and biochemical process of decomposition, accumulation

and turnover of SOM, There are marked differences of SOM carbon dynamic

between intercropping and monocropping systems Fable 1).

The annual C input in the intercropping system from 1990 to 2015 was

constant at 1.5 t ha-' and in the monocropping system 0.8 t ha". Litter structural C

content in the surface of the intercropping system is constant at 280 kg ha" from

1990 to 201 5, and in the monocropping system 120 kg ha''. Litter structural C in

soi1 from the intercropping system is increasing from 1990 to 201 5. amounting to 2.5

t ha-' in 201 5; in the monocropping system, it decreases, and is 0.5 t ha" in 201 5.

This is a 5-fold difference. C in the active SOM in the surface of the intercropping

system increases from 1990 to 2015 and amounts to 120 kg ha"; in the

monocropping system, it is only 27 kg ha-'. C in passive SOM in both the

intercropping and monocropping systems decreases slightly. Total soi1 C including

belowground structural and metabolic components in the intercropping system

increases slightly from 1990 to 2015 (45 t ha-'), and in the monocropping systern

decreases (32 t ha-') (Fig. 6.7. 6.8). The sum of C in wood components in the

intercropping system increases from 1990 to 2015 (4.7 t ha-'), and remains at zero

in the monocropping system (O t ha") since there is no organic rnatter input source

from trees in this system. The total C (Le. sum of soi1 organic matter, trees dead

wood, forest litter) in the intercropping system increases from 1988 to 2015 and

amounts to 70 t ha-'; in the monocropping system, it decreases slowly from 1988

96

Fie- 6-7. Total soi1 C in intercropping system

.- - -, - --

1960 1970 $980 f 990 2000 2010 2020

1 ime

Fig. 6.8. Total soi1 C in monocropping system

1990 2000

Time

to 2015 (35 t ha-'). C from organic leaching in stream fiow in the intercropping

system increases slowly from I W O to 201 5 and arnounts to 0.2 kg ha-' in 201 5;

in the monocropping system. it decreases to 0.1 kg ha-'.

Soil respiration is an indicator of intensity of biological activity. Annual CO,

respiration from decomposition in intercropping systern increases from 1990 to 201 5

and amounts to 1 -7 kg ha-' yr' ; the in

ha-' yrl. The annual accumulator for

SOM decornposition in intercropping

monocropping system. it decreases to 1.0 kg

CO, loss due to microbial respiration during

system increases slowly frorn 1 990 to 201 5,

and amounts to 300 kg ha-' yr'; in the monocropping system, it decreases to 200

kg ha-' yr'.

Soil Organic Matter Nitrogen Dynarnics

SOM N also is a main component of SOM. SOM N dynarnics represent the

biological and biochemical processes for assimilation, mineralization. nitrification

and imrnobilization of SOM- There are marked differences in SOM N between

intercropping and monocropping systems (Table 2).

The total N in the intercropping system was constant (4 t ha-') from 1990 to

201 5. and in monocropping system decreased slowly to 3.8 t ha-' (Fig. 6.9. 6.1 0).

Structural N in litter in the intercropping systern increased from 1990 to 201 5 and

amounted to 1.4 kg ha-'; in themonocropping systern. it decreased to 0.5 kg ha-'.

N in active SOM in the intercropping system increases from 1990 to 2015 and

amounts to 8 kg ha", and in the monocropping system decreases to 2.2 kg ha-'. N

98

Fig. 6.9- Total soi1 N in intercropping system

O 1960 1970 1980 1990 ZOO0 2010 ZOZO

Tim e

Fig. 6.10. Total soi1 N in monocropping system

1960 1970 1980 1990 2000 2010 2020

Tim e

in passive SOM in both intercropping and monocropping systems decreases. N

from organic leaching in stream flow in the intercropping system is constant at 20

g ha*'. N from mineral leaching stream flow Ri the intercropping system goes to zero

in 1990 and remains in constant until 2015; in the monocropping system, the

mineral N leaching of stream flow is retained at 1.5 g ha-'. The study shows that

trees in an intercropping system can be used to remedy N contamination from

agricultural systems. improving water quality and protecting environment.

CONCLUSION

From a comparison of SOM residue. SOM carbon and SOM nitrogen. the

SOM regime in intercropping system has clear superiority. The SOM residue is 4

tirnes the amount of the monocropping system. the SOM carbon is double and the

SOM nitrogen is more while at the same time the minera1 N in stream flow is lower.

ACKNOWLEDGEMENTS

I would Iike to thank Dr. R. Paul Voroney and Dr. Andrew M. Gordon for their

helpful comments.

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