wood ash effects on soil solution and nutrient budgets in a willow bioenergy plantation

WOOD ASH EFFECTS ON SOIL SOLUTION AND NUTRIENTBUDGETS IN A WILLOW BIOENERGY PLANTATION

BYUNG BAE PARK, RUTH D. YANAI, JAMES M. SAHM,BENJAMIN D. BALLARD and LAWRENCE P. ABRAHAMSON

SUNY College of Environmental Science and Forestry, Syracuse, NY 13210, U.S.A.(∗author for correspondence, e-mail: [email protected], Fax: +1 315 470-6934,

Tel:+1 315 470-4742)

(Received 13 October 2003; accepted 3 June 2004)

Abstract. The management of wood ash is an important factor in the environmental and economicanalysis of wood burning. Wood ash can be applied to energy crops as a fertilizer, which can helpreplace nutrients removed during harvest. The objectives of this study were to examine the temporaland spatial dynamics of nutrient elements applied in wood ash to an intensively cultured, short-rotationwillow bioenergy system. Wood ash was applied at the rates of 10 and 20 Mg ha−1 yr−1 to coppicedwillow, Salix purpurea, clone SP3, from 1992 to 1994. The relative abundance of nutrients in appliedwood ash was Ca > K > Mg > P > N. There was little effect of wood ash on N or P concentrationsin soil solution measured at 20 and 40 cm depth. Soil solution concentrations of base cations wereelevated in the last two years of the study by 30 to 90%, depending on the element and treatment,in plots receiving wood ash. Wood ash treatments had little influence on foliar leaching. Wood ashtreatment also had few significant effects on willow growth or on the contents of N, P, K, Ca, andMg in foliage and stems. The addition of P, K, Ca, and Mg in wood ash was more than enough tocompensate for harvest removals and leaching losses. This study demonstrated that wood ash cansupply most nutrients removed during harvest in willow plantations, with the exception of N, withoutadverse effects on groundwater or vegetation.

Keywords: biomass, nutrient input-output, Salix purpurea, short-rotation, soil solution, throughfall

1. Introduction

Woody biomass is an important alternative to fossil fuel. Biomass or bioenergyplantations utilize fast growing hardwood species, such as Salix spp. and Populusspp., that coppice vigorously following harvest, potentially yielding many succes-sive crops with rotations ranging from 1 to 4 yr.

Wood ash is generated during the process of burning wood for energy. The mostabundant elements in wood ash are Ca and K, followed by Mg, Al, Fe, and P.Micronutrients potentially toxic in high concentrations, such as Cd, Cu, Zn, Pb,As, and Cr may also be present. Nitrogen, including organic and inorganic forms,is low in wood ash because most of it is volatilized during combustion.

Wood ash could become an important industrial problem as wood is increas-ingly used as an energy source, as landfill capacity for wastes becomes limited,and as disposal costs rise (Campbell, 1990). Waste management programs are

Water, Air, and Soil Pollution 159: 209–224, 2004.C© 2004 Kluwer Academic Publishers. Printed in the Netherlands.

210 B. B. PARK ET AL.

required to dispose wood ash in a cost-effective and environmentally acceptablemanner.

Many investigators have examined the possibilities of wood ash utilization onagricultural lands as an alternative liming agent and fertilizer (Erich, 1991; Meyersand Kopecky, 1998; Naylor and Schmidt, 1986). This same practice has beenproposed for fiber production (Arvidsson and Lundkvist, 2003; Hytonen, 1998;Moilanen et al., 2002). The potential benefits of a land-disposal program for woodash include improvement in crop productivity and soil fertility.

However, in order for land application of wood ash to be a viable alternative, it isessential to test for adverse effects on soil properties, groundwater, and vegetation.To date, few field studies have connected wood-ash moderated changes in the soilsystem with nutrient leaching, as most are concerned with effects on crop productionand plant elemental concentrations.

The objective of this study was to describe biogeochemical changes associatedwith land application of wood ash in an intensively cultured, short-rotation willowbioenergy system in central New York. Internal system cycling was monitoredthrough collection and analysis of throughfall and leaf litter. Stemflow was notmeasured because of the large number of stems in a willow coppice system. The fateof wood ash components in the system was described using a budgetary approach,monitoring nutrient inputs in the form of wood ash application and atmosphericdeposition, and outputs due to harvest removals and soil solution leaching loss.

2. Material and Methods

2.1. STUDY SITE

The study site is located at the Forestry Genetics Field Station of the State Universityof New York College of Environmental Science and Forestry in Tully, New York(42◦47′N, 76◦7′E). The site receives approximately 105 cm of precipitation annually(30-yr average, Volk, 2002), with about 55 cm falling during the growing season,from May through September. The soil at the site is a Palmyra gravely silt loam,which is a Glossoboric Hapludalf, on 0 to 3% slopes (Hutton and Rice, 1977).Because it is derived from limestone and shale outwash and till, the pH is relativelyhigh, ranging from 5.8 to 6.8 (Volk, 2002). This agricultural soil is deep and welldrained, with a medium to heavy texture, 24% clay to a depth of 40 cm, and coarsefragment fraction of up to 32% in the 20–40 cm layer (Sahm, 1995).

2.2. EXPERIMENTAL DESIGN

The current study was conducted on an existing split-plot design with three repli-cates of each treatment (Figure 1). Fertilization with two levels (fertilized and un-fertilized) was the whole-plot factor in the original design. Fertilized plots received

WOOD ASH EFFECTS ON NUTRIENT BUDGETS IN A WILLOW PLANTATION 211

30 cm

15 cm

45 cm

15 cm

45 cm

30 cm

45 cm

30 cm

15 cm

30 cm

15 cm

45 cm

15 cm

45 cm

30 cm

45 cm

30 cm

15 cm

20 Mg ha-1 ash 0 Mg ha-1 ash 10 Mg ha-1 ash

20 Mg ha-1 ash 0 Mg ha-1 ash 10 Mg ha-1 ash

Blo

ck 1

Blo

ck 2

Tre

e sp

acin

gP

lot b

ound

ary

Lysi

met

ers

Thr

ough

fall

&

litte

r tr

aps

Figure 1. Plot layout showing location of sampling devices and treatment plots receiving wood ashtreatments of 0, 10, and 20 Mg ha−1. Three precipitation collectors are located outside of the plotboundary. Block 1 and Block 2 received different fertilization treatments in a prior experiment.

336 kg ha−1 N, 112 kg ha−1 P, and 224 kg ha−1 K annually as ammonium nitrate,treble superphosphate and muriate of potash, respectively, from 1987 to 1991, ex-cept that in 1990 N was applied as urea through an irrigation system (Kopp et al.,2001). Density with three levels of spacing (15, 30, and 45 cm) was established asthe sub-plot factor in the spring of 1987. The current study was designed to mini-mize the effect of these other treatments. Spacing effects were ignored by treating


three spacing plots as one experimental unit, and past fertilization effects wereeliminated by blocking (Kuehl, 2000). By treating in this manner, variation due tospacing would be equally distributed across all wood ash treatments and levels ofpast fertilization. The plots were planted with willow clone SP3 (Salix purpurea)in 1987 using dormant hardwood cuttings 25 cm in length. Plots were harvestedannually after leaf fall from 1987 to 1991.

Wood ash was provided by the Lyons Falls Pulp and Paper Company, Lyons Falls,New York. The ash was homogenized prior to application. The moisture content ofthe ash was determined by drying at 105 ◦C and used to calculate the desired appli-cation rates. Wood ash was applied to treatment plots in late April before bud breakin 1992, 1993, and 1994 at the rates of 0 (control), 10, and 20 Mg ha−1. Subsamples(0.5 kg) were collected at the time of application for chemical characterization.

2.3. WOOD ASH CHARACTERISTICS

The chemical properties of wood ash that were determined included pH, total N,P, K, Ca, and Mg. Extractable metal concentrations including Cr, As, Se, Ag,Cd, Ba, Hg, and Pb were determined through the toxic characteristic leachingprocedure (U.S. EPA, 1992). Ash pH was determined from one 20 g subsamplefrom each plot (n = 12), in 2:1 deionized water: ash mix using a glass electrode(Orion Research Digital Ionanalyser Model 601A). Nitrogen concentration wasdetermined by the macro-Kjeldahl method (Bremner, 1965) and P concentrationwas determined colorimetrically with vanadate-molybdate (Wilde et al., 1972).After dry ashing the samples at 470 ◦C, the ash was dissolved in 10 mL of 6 N HCl.Concentrations of K, Ca, and Mg in the acid solution were determined by atomicabsorption spectrophotometry (AAS).

2.4. VEGETATION ANALYSES

Foliage for chemical analysis was sampled each year at the end of August from1992 to 1994 by selecting six stems randomly from the center of each plot andstripping all leaves from the entire length of stem.

Litter was collected weekly from mid-June through leaf fall in November from1992 to 1994 with samples composited on a calendar month basis. Leaves wereremoved from a tray-style collector (33 cm × 20 cm) and returned to the laboratoryfor chemical analysis. Seasonal litter biomass was calculated by adding the dryweights (65 ◦C) of monthly litter samples.

Woody biomass production (Mg ha−1) was obtained by entirely harvesting eachplot in December each year. Foliar biomass was estimated by sampling six stems,stratified by relative stem size (small, medium, and large), collected in July frominterior border rows of each plot. Leaves from each plot were dried to a constantweight at 65 ◦C and weighed.


Litter, foliage, and biomass samples were dried at 65 ◦C and ground in a Wileymill to pass a 1 mm screen. All samples were analyzed for N, P, K, Ca, and Mg,following the same methods described above for wood ash analysis.

2.5. SOLUTION COLLECTION AND ANALYSES

Soil solution was collected with porous ceramic cup tension lysimeters. Two lysime-ters were installed in each plot in January of 1992, one at 20 cm soil depth andthe other at 40 cm soil depth, for a total of 18 lysimeters at each depth. Lysimeterswere sampled weekly throughout the year, except in winter when access tubes wereblocked with ice.

Throughfall was collected weekly in each plot from mid-June through leaf fallin November, using a tray-style collector designed to accommodate the low growthhabit of coppiced willow in the spring. These samplers also served as litter traps.Each plot contained one randomly located throughfall collector/litter trap, for atotal of 18 collectors.

Bulk deposition was collected weekly from April through November using fun-nel collectors placed in three locations around the study site. During winter months,bucket collectors were used for snow.

All precipitation and soil solution samples were weighed to estimate volume,then filtered and frozen until chemical analysis. Monthly composites of weeklysamples were analyzed for NO3, NH4, PO4, K, Ca, and Mg. Concentrations of K,Ca, and Mg in solutions were determined by AAS. Phosphate and NO3 concen-trations were determined by ion chromatography, and NH4 was measured with theindophenol blue method (Keeney and Nelson, 1982).

2.6. NUTRIENT FLUX

The net loss or net accumulation (kg ha−1) of each nutrient on each plot was cal-culated by summing inputs from wood ash application (kg ha−1) and precipitation(kg ha−1), and subtracting leaching (kg ha−1) and harvest losses (kg ha−1). Nutri-ent removal by harvesting was calculated by Park et al. (2004). Throughfall andlitterfall cycle nutrients within the plot do not affect overall system balance.

To estimate nutrient fluxes in soil solution requires an estimate of water flux. Weassumed that a constant fraction of incoming precipitation passes by each lysimeterdepth in the soil. At 20 cm, we used 55% of incoming precipitation (i.e., 45% isevaporated or transpired) and we used 45% of incoming precipitation at 40 cm (i.e.,an additional 10% is removed by root uptake between 20 and 40 cm) (Luxmoore,1983; Yanai, 1991). Soil solution fluxes were not estimated during the winter.During snowmelt in the spring, we assumed all melt water moved through the soilprofile.


2.7. DATA ANALYSES

A completely randomized design was used to compare the contents of appliedwood ash among years. Solution and vegetation nutrients were analyzed using acompletely randomized block design with three wood ash treatment levels (0, 10,and 20 Mg ha−1) and two blocks based on previous fertilization practices (fertilizedand unfertilized). Analysis of variance procedures with LSD multiple comparisontests were used to test the effect of wood ash application on soil solution andvegetation.

3. Results and Discussion

3.1. WOOD ASH CHARACTERIZATION

Nutrient contents of the applied wood ash varied over the three years of application(Table I). Nutrient additions in wood ash were significantly lower in 1994 than1992 because the insoluble fraction was greater (Park et al., 2004). Potassium, Ca,and Mg additions in 1994 were less than half of those in 1992. Although our woodash was always from the same source, its characteristics could vary with the treespecies burned, soil properties of the area from which the wood was harvested, andamount of bark burned (Campbell, 1990).

The relative abundance of nutrients in the wood ash was Ca � K > Mg > P �N. Except for N, the rate of additions of these nutrients was adequate to maintainwillow growth (Perttu, 1999). The ideal proportions by weight of the most importantmineral nutrients for maximum willow production are 100:14:72:7:9 for N, P, K,Ca, and Mg (Ericsson, 1981; Perttu, 1999). The elemental composition of woodash in this study (1:10:50:193:17 for N, P, K, Ca, and Mg) was clearly far from

TABLE I

Nutrient additions to a willow plantation with wood ash applications of 10 and 20 Mg ha−1 in1992, 1993, and 1994

Treatment(Mg ha−1) Year N (kg ha−1) P (kg ha−1) K (kg ha−1) Ca (kg ha−1) Mg (kg ha−1)

10 1992 9 (0.2)a 60 (3.9)a 387 (32)a 1649 (157)a 137 (3.1)a

1993 6 (0.3)b 41 (0.4)b 327 (7)b 968 (12)b 92 (3.2)b

1994 3 (0.2)c 46 (1.3)b 157 (2)c 702 (7)c 62 (0.7)c

20 1992 17 (0.1)a 109 (8.2)a 682 (40)a 2960 (123)a 245 (4.5)a

1993 11 (0.5)b 80 (0.9)b 617 (5)b 1903 (31)b 190 (2.0)b

1994 5 (0.3)c 93 (1.9)c 307 (4)c 1429 (18)c 125 (1.2)c

Standard errors are in parentheses (n = 12). Means within the same column and treatment withthe same letter are not significantly different at α = 0.05.


optimal. Although wood ash provides little N, it can improve the base status of thesoil to which it is applied. The average pH of the wood ash was 10.6, which wasnot as high as that found in other studies (Someshwar, 1996).

Trace metal content in the ash was low in our study. Most trace metals werebelow detection limits (0.05 mg L−1 As, 0.05 mg L−1 Ba, 0.075 mg L−1 Cd,0.25 mg L−1 Pb, and 0.25 mg L−1 Se). Barium was detected at 3.0 and 2.6 mg L−1

in 1992 and 1993, respectively, and Ag at 0.04 mg L−1 in 1993. These were lowcompared with EPA standards for regulatory limits (100 mg L−1 Ba and 5 mg L−1

Ag). Similar results have been observed in other studies (e.g., Krejsl and Scanlon,1996; Williams et al., 1996). Ludwig et al. (2002) found no significant change inheavy metal content in the organic layer in a pine stand after wood ash application.Wood ash of this type, i.e. from clean fuel consisting of bark and whole-tree chips,is generally free of metal contaminants (Milford et al., 1991).

3.2. NUTRIENT CONTENT OF VEGETATION

The nutrient contents of willow foliage and stems were similar in plots treatedwith wood ash and in controls (Table II); few contrasts were statistically signif-icant even at α = 0.10. The nutrient content of litter was significantly greaterin plots receiving 20 Mg ha−1 wood ash, except for Ca (Table II). These dif-ferences were small compared to the amount of nutrients applied in wood ash.Plots receiving 10 Mg ha−1 were not significantly different from controls even atα = 0.10.

In other studies, wood ash has sometimes increased nutrients in vegetation.Norway spruce needles had higher needle concentrations of P, K, and Ca five yearsafter wood ash application (Arvidsson and Lundkvist, 2003). Rates of wood ashapplication greater than 16 Mg ha−1 improved tree growth on a drained pine mirein Finland (Moilanen et al., 2002). Wood ash application increased foliar K andNa concentrations of red maple seedlings growing on O-horizon but not B-horizonsoils (Unger and Fernandez, 1990). The greatest effects are seen in sites with lowpH; our site is near neutral (pH = 6.4).

Nutrient contents of willow foliage, litter, and stems decreased over the threeyears of our study, associated with reductions in biomass in this annually coppicedsystem (Park et al., 2004). The number of stems was fewer in the treated plots (64stems per stool) (p = 0.01) than control plots (73 stems per stool) (Park et al., 2004).There was no difference in biomass associated with the application of wood ash(p = 0.75, 0.49, and 0.74 in 1992, 1993, and 1994, respectively), because the stemsgrew larger when there were fewer of them. Weeds were not included in estimatesof biomass production or nutrient contents in this study, although we observedweeds in all the plots. Weed competition with white bean (Ailanthus triphysa)has been observed to reduce biomass production with N:P:K fertilizer treatments(Shujauddin and Kumar, 2003).


TAB

LE

II

Folia

r,lit

ter,

and

stem

biom

ass

nutr

ient

cont

enti

na

will

owpl

anta

tion

rece

ivin

gw

ood

ash

appl

icat

ions

of0,

10,a

nd20

Mg

ha−1

in19

92,1

993,

and

1994

Folia

ge(k

gha

−1)

Litt

er(k

gha

−1)

Stem

kgha

−1T

reat

men

tY

ear

Mg

ha−1

NP

KC

aM

gN

PK

Ca

Mg

NP

KC

aM

g

1992

064

.5a

5.3a

59.7

a46

.4a

5.7a

36.5

a3.

2a18

.7a

41.3

a3.

5a52

.4a

9.4a

33.4

a33

.6a

3.8a

(1.7

)(0

.3)

(4.2

)(3

.3)

(0.4

)(4

.1)

(0.4

)(2

.4)

(3.7

)(0

.4)

(5.0

)(0

.6)

(6.0

)(1

.4)

(0.2

)

1056

.7b

5.0a

54.8

a43

.5a

5.4a

29.9

b2.

6b16

.3a

33.2

b2.

9b50

.3a

9.2a

31.9

a32

.6a

3.8a

(2.2

)(0

.2)

(4.0

)(1

.9)

(0.2

)(2

.7)

(0.2

)(2

.5)

(3.0

)(0

.3)

(4.1

)(0

.6)

(4.0

)(2

.0)

(0.1

)

2061

.5a,

b5.

0a59

.4a

45.2

a5.

6a36

.4a

3.0a,

b18

.9a

37.9

a,b

3.3a,

b57

.2a

9.7a

29.1

a30

.4a

3.9a

(3.1

)(0

.2)

(3.7

)(2

.8)

(0.3

)(4

.7)

(0.3

)(2

.2)

(2.9

)(0

.3)

(3.9

)(0

.5)

(4.9

)(1

.6)

(0.1

)

1993

046

.1a

4.1a

38.3

a37

.9a

4.5a

18.7

a1.

6b10

.9b

23.5

a2.

1a,b

27.9

a4.

9a17

.8a

21.7

a2.

2a

(4.6

)(0

.4)

(3.8

)(3

.4)

(0.3

)(3

.0)

(0.3

)(2

.2)

(2.9

)(0

.2)

(2.5

)(0

.5)

(1.9

)(1

.7)

(0.2

)

1051

.2a

4.8a

43.0

a44

.6a

5.1a

16.9

a1.

7b12

.7b

24.7

a2.

0b31

.6a

5.5a

20.3

a25

.8a

2.6a

(4.5

)(0

.5)

(3.6

)(3

.6)

(0.6

)(1

.5)

(0.1

)(1

.9)

(2.2

)(0

.1)

(2.5

)(0

.4)

(1.7

)(2

.6)

(0.3

)

2051

.9a

4.5a

42.4

a38

.7a

4.5a

21.7

a2.

3a20

.2a

29.5

a2.

6a30

.0a

5.2a

19.0

a24

.0a

2.5a

(4.6

)(0

.4)

(4.7

)(2

.9)

(0.3

)(1

.5)

(0.2

)(2

.2)

(2.4

)(0

.3)

(2.5

)(0

.4)

(1.4

)(1

.3)

(0.2

)

1994

034

.1a

3.6a

37.1

a29

.5a

4.1a

21.1

b2.

1b10

.6b

23.0

a2.

2b31

.6a

5.5a

19.4

a21

.7a

2.7a

(5.7

)(0

.5)

(6.0

)(3

.6)

(0.6

)(4

.0)

(0.4

)(1

.5)

(2.8

)(0

.3)

(3.5

)(0

.5)

(2.3

)(2

.1)

(0.3

)

1033

.0a

3.6a

35.9

a29

.4a

3.7a

21.7

b2.

2b14

.0b

25.2

a2.

2b27

.9a

5.4a

18.4

a20

.4a

2.5a

(4.8

)(0

.5)

(5.6

)(4

.5)

(0.4

)(2

.1)

(0.2

)(2

.3)

(2.0

)(0

.1)

(3.4

)(0

.6)

(2.1

)(2

.9)

(0.4

)

2030

.3a

3.5a

33.4

a23

.5a

3.2a

31.9

a3.

1a19

.3a

28.7

a3.

0a26

.6a

5.2a

18.0

a17

.9a

2.2a

(4.1

)(0

.4)

(4.3

)(2

.2)

(0.3

)(3

.3)

(0.3

)(2

.4)

(2.2

)(0

.3)

(2.9

)(0

.5)

(1.6

)(1

.6)

(0.2

)

a Stan

dard

erro

rsar

ein

pare

nthe

ses

(n=

6).M

eans

with

inth

esa

me

colu

mn

and

year

with

the

sam

ele

ttera

reno

tsig

nific

antly

diff

eren

tatα

=0.

10.O

nly

four

ofth

ese

cont

rast

sas

sign

ifica

ntat

α=

0.05

.


3.3. SOLUTIONS

There were no significant differences in pH of the soil solution between plotstreated with wood ash and controls (Figure 2). Soil solutions were significantlymore acidic at 20 cm than at 40 cm depth in 1992 and 1993, but not in 1994. Other

Time (Month)

Con

cent

ratio

n (m

g L-1

)

0

1

2

3

4

50

10

20

30

400

2

4

6

8

100.0

0.1

0.2

0.3

0.4

0.5

0.602468

101214

Control

10 Mg ha-1

20 Mg ha-1

- Lo

g[H

+]

5

6

7

8

9

10(a)

4 5 6 7 8 9 10 11 4 5 6 7 8 9 10 11 4 5 6 7 8 9 10 11

Mg

Ca

K

P

N

pH

1993 19941992

aa

b

aa

b

a

b

a

bb

aab

b

a

b

b

a

ab

b

aab

b

aa

b

a

a

b

aa

b

a

a

b

aa

b

a

a

b

a

a

b

Figure 2. Nutrient concentrations and pH of soil solutions at (a) 20 cm and (b) 40 cm soil depth forplots receiving 0, 10, and 20 Mg ha−1 wood ash treatments in 1992, 1993, and 1994. Different letterswithin each month showed significant differences among wood ash treatments at α = 0.10.

(Continued on next page)


0

1

2

3

4

50

10

20

30

400

2

4

6

8

100.0

0.1

0.2

0.3

0.4

0.5

0.60

3

6

9

12

15

4 5 6 7 8 9 10 11 4 5 6 7 8 9 10 11 4 5 6 7 8 9 10 11

Mg

Ca

K

N

1993 19941992

P

5

6

7

8

9

10pH

Time (Month)

Con

cent

ratio

n (m

g L-1

)-

Log[

H+]

abb

abb

a

a

b

aa

b

aa

b

aa

b

abb

a

bb

a

ab

b

a

bb

a

bb

a

bc

abb

a

bb

a

bb

a

bb

a

bb

a

bb

Control10 Mg ha-1

20 Mg ha-1

(b)

Figure 2. (Continued )

studies have shown significant elevation of soil solution pH by wood ash treatment(e.g., Genenger et al., 2003; Kahl et al., 1996; Staples and Van Rees, 2002). Theseother studies were on soils that were more acidic than our site.

Application of wood ash increased concentrations of K, Ca, and Mg in soilsolutions at various depths and time, but little effect was observed on N and P(Figure 2). High concentrations of N (nitrate and ammonium) in soil solution wereobserved at the beginning of the study irrespective of treatment, probably due tomineralization induced by soil disturbance when the lysimeters were installed. After


the first year, N concentrations were less than 0.3 mg L−1 (Figure 2). Similarly, therewas no discernible pattern for solution N concentration with wood ash applicationrates (Williams et al., 1996). In some studies, N in soil solution increased withwood ash amendment due to increased nitrification (Kahl et al., 1996; Staples andVan Rees, 2001).

The response of soil solution P to wood ash treatment was insignificant exceptfor lower concentrations in the treated compared with control plots at 20 cm depthin the second year of the study (Figure 2). Staples and Van Rees (2001) found aconsistent increase in solution P with wood ash amendment, while Williams et al.(1996) found no significant effect.

Potassium concentrations in soil solution at 40 cm depth were consistently ele-vated by wood ash application (Figure 2). At 20 cm depth, however, K concentra-tions were not higher than the controls until the third year of the study (1994), andthis difference was due as much to a decrease in controls over time as to an increasein the treated plots. Other studies have reported increases in K in soil solution due towood ash application (Eriksson, 1998; Meiwes, 1995; Williams et al., 1996). In ourstudy, K was also the nutrient most elevated by wood ash application. Potassiumconcentrations were elevated by 70% at the lower rate of wood ash application and91% at the higher rate, averaging over the 20 and 40 cm lysimeter depths over the last2 yr of the study. Calcium and Mg concentrations were also significantly elevatedby wood ash application in the latter half of our study. Calcium and Mg concen-trations were both elevated 30% by wood ash applications of 10 Mg ha−1 yr−1. Atthe higher application rate, Ca and Mg were elevated by 53 and 43%, respectively.

Nutrient concentrations in soil solution were multiplied by estimates of solutionflux to describe patterns of nutrient leaching (Table III). The rates calculated for1992 are high and probably reflect soil disturbance following lysimeter installation(lysimeters were installed in January, 1992). Rates were not calculated for 1993because the lysimeter data were incomplete. In the third year of the study, 1994,leaching of K, Ca, and Mg at both soil depths was consistently greater in wood-ashtreated plots than in controls.

Changes in nutrient leaching from foliage due to wood ash application wouldindicate an effect of treatment on plant nutrition. In this study, wood ash treatmentshad little influence on foliar leaching (Table IV). In the second year of the study,throughfall had higher concentrations of K and Ca at the higher level of woodash application. In all plots, throughfall contained much more K and Ca than didprecipitation (Table IV).

3.4. BUDGETS

Nutrient input-output budgets were calculated by subtracting nutrient losses throughbiomass harvest and leaching from nutrient inputs due to ash treatment and pre-cipitation (Figure 3). In the control plots, there was a net loss of all elements with


TABLE III

Total nutrient and water flux in a willow plantation with wood ash applications of 0, 10, and 20 Mgha−1 in 1992 and 1994

Treatment N P K Ca Mg Water fluxYear (Mg ha−1) (kg ha−1) (kg ha−1) (kg ha−1) (kg ha−1) (kg ha−1) (m3 ha−1)

1992 20 cm Lysimeter

0 19.9 (5.6) 0.6 (0.3) 38 (16.8) 60 (9.7) 15 (4.7) 5749

10 13.4 (3.9) 0.5 (0.2) 28 (9.6) 55 (12.0) 10 (2.7) 5749

20 9.4 (2.7) 0.2 (0.1) 23 (7.7) 45 (5.4) 6 (1.3) 5749

40 cm Lysimeter

0 13.5 (4.1) 0.3 (0.1) 8 (2.7) 31 (6.7) 6 (1.5) 4704

10 11.2 (4.3) 0.2 (0.1) 17 (9.1) 33 (7.2) 7 (2.2) 4704

20 17.6 (4.2) 0.1 (0.1) 15 (5.7) 31 (4.1) 5 (0.9) 4704

1994 20 cm Lysimeter

0 1.3 (0.2) 1.7 (0.2) 18 (6.6) 70 (25.2) 14 (5.0) 7024

10 1.2 (0.2) 1.7 (0.2) 24 (6.4) 103 (28.1) 19 (5.8) 7024

20 1.2 (0.2) 0.9 (0.2) 39 (16.7) 91 (19.1) 18 (5.3) 7024

40 cm Lysimeter

0 1.9 (0.3) 0.8 (0.2) 3 (0.7) 35 (10.0) 5 (1.3) 5747

10 0.6 (0.2) 0.7 (0.2) 13 (6.4) 32 (6.5) 7 (2.2) 5747

20 0.6 (0.2) 0.7 (0.1) 15 (6.6) 36 (8.1) 10 (3.3) 5747

40 cm flux represents system leaching output during the growing season.Standard errors, in parentheses, are based on variation in solution chemistry (n = 6), as the waterflux is simulated at the site level.

biomass removal and leaching. With the application of wood ash, all elementsexcept for N showed net accumulation. Wood ash cannot compensate for harvestremovals of N, because it contains little N. The rate of nutrient accumulation inplots receiving 20 Mg ha−1 wood ash were nearly twice the rates at the 10 Mg ha−1

treatment level. The net loss and accumulation of nutrients were smaller in 1994than in 1992, because the acid-soluble fraction of wood ash decreased over time(Park et al., 2004).

The rate of nutrient accumulation in soils was measured at this site (Park et al.,2004; Sahm, 1995), and can be compared with the budgeted changes in storage inthe plots shown in Figure 3. The changes in soil storage were small compared withthe amounts of nutrients that should have been detected. The rate of accumulationof the major cations in the top 10 cm of soil was less than 20% of the amountapplied in wood ash. One pool not measured in either study is the ash remainingon the surface of the soil. Other possibilities are that ash is lost by overland flow orby wind, or that flow is underestimated by lysimeters.


TABLE IV

Throughfall and precipitation nutrients in a willow plantation receiving wood ash applications of 0,10, and 20 Mg ha−1 in 1992, 1993, and 1994

TreatmentYear (Mg ha−1) N (kg ha−1) P (kg ha−1) K (kg ha−1) Ca (kg ha−1) Mg (kg ha−1)

1992 Throughfall

0 1.2 (0.1) 0.2 (0.0) 26.7 (3.8) 8.7 (1.2) 2.4 (0.3)

10 1.1 (0.1) 0.2 (0.0) 22.8 (5.2) 7.8 (1.6) 1.5 (0.3)

20 1.2 (0.1) 0.3 (0.1) 27.8 (1.0) 9.3 (1.0) 1.8 (0.0)

Precipitation 11.1 1.4 3.4 4.8 1.3

1993 Throughfall

0 – 1.3 (0.1) 16.1 (1.7) 4.9 (0.3) 1.1 (0.0)

10 – 1.4 (0.4) 16.4 (1.1) 5.9 (0.3) 1.2 (0.1)

20 – 1.7 (0.4) 24.4 (0.4) 8.5 (1.0) 1.5 (0.0)

Precipitation – 1.5 1.4 1.0 0.9

1994 Throughfall

0 – – 38.8 (5.0) 9.3 (0.4) 2.5 (0.1)

10 – – 33.7 (2.9) 9.4 (0.5) 2.3 (0.0)

20 – – 48.8 (8.6) 10.2 (1.0) 2.4 (0.4)

Precipitation – – 3.7 8.0 1.8

Nutrient inputs due to precipitation are assumed uniform across all treatments.Standard errors are in parentheses (n = 2). ‘–’ represents missing values.

4. Conclusions

Land application of wood ash as a fertilizer and liming agent is a cost-effective andenvironmentally acceptable alternative to disposal in landfills. As a liming agent,wood ash neutralizes soil acidity, with at least half the efficiency of commercialliming materials (Naylor and Schmidt, 1986). Wood ash acts as a low-N fertilizer(1:10:50 as N:P:K) and substantially adds to the base status of the soil to which itis applied. The physical and chemical properties of wood ash depend on the sourceof the wood, but heavy metal concentrations in the ash are generally low, such thatthere is little danger of contaminating groundwater.

In this study, wood ash treatments increased K, Ca, and Mg concentrations insoil solution with little effect on plant nutrient conditions or plot biomass produc-tion. Input-output budgets showed net accumulation of P, K, Ca, and Mg on siteat both treatment levels, in spite of intensive harvest removals. In other words,wood ash supplied most of the nutrients (except N) removed during short-rotationintensive culture of willow plantations, without adversely affecting ground wateror vegetation. A greater benefit of wood ash application to plant production mightbe expected on sites with acidic soils or pH-induced nutrient deficiencies.


Nut

rien

t Net

Flu

x (k

g ha

-1)

-20

0

20

40

60

80

100

120

Ash Application Rate (Mg ha-1)

-100

0

100

200

300

400

500

600

700Ash Application Rate (Mg ha-1)

Nut

rien

t Net

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x (k

g ha

-1)

0 10 20 0 10 20

-70

-60

-50

-40

-30

-20

-10

0

10 3000

2500

2000

1500

1000

500

0

-500

250

200

150

100

50

0

-50

0 10 20 0 10 20

1992 1994 1992 1994

a. N

b. P

c. K

e. Mg

d. Ca

Figure 3. Net elemental flux for April through December in the treatment plots receiving 0, 10,and 20 Mg ha−1 wood ash. The net flux (kg ha−1) of each nutrient on each plot was calculated bysumming inputs from wood ash application (kg ha−1) and precipitation (kg ha−1), and subtractingleaching (kg ha−1) and harvest losses (kg ha−1).

Acknowledgements

Fieldwork was conducted by crews at the Forestry Genetics Field Station of theState University of New York College of Environmental Science and Forestry. TimVolk and Don Koo Lee made helpful suggestions on the manuscript. This researchwas supported by the New York State Energy Research and Development Authority,the Electric Power Research Institute, the Department of Energy, and the USDABiomass Power for Rural Development Program.


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wood ash effects on soil solution and nutrient budgets in a willow bioenergy plantation

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