Infiltration under no-till and conventionaltillage systems in Saskatchewan

C.P. MAULE and W.B. REED

Agricultural and Bioresource Engineering Department, University of Saskatchewan, Saskatoon, SK, Canada S7N 0W0.Received 18 November 1992; accepted 6 May 1993.

Maule, C.P. and Reed, W.B. 1993. Infiltration under no-till andconventional tillage systems in Saskatchewan. Can. Agric. Eng.35:165-173. The effects of no-till and conventional tillage systemson water infiltration and related soil parameters were investigated infive fields under dryland farming in southern Saskatchewan. A rainfall simulator was used for the infiltration measurements. Threefields were under a no-till system for different lengths of timeranging from 5 years to 13 years. A heavy duty cultivator was usedin both fields under conventional tillage; one field was under continuous cropping, and the other under a traditional wheat-fallowrotation. Fields under the no-till system had higher organic mattercontents, higher macroporosities, and higher saturated hydraulicconductivities than the fields with the conventional tillage. Organicmatter in the no-till and conventional continuously cropped fieldsincreased approximately 0.2% for every year since the last conventional fallow-crop rotation. The field in conventional fallow had thelowest infiltration rates, while the conventional continuouslycropped field had the highest infiltration rates, although not significantly different than those from the 13 year old no-till field.Cumulative infiltration at 60 minutes was most highly correlatedwith organic matter content; for every 1 percentage point increase inorganic matter, cumulative infiltration increased by 9 mm.

Leseffetsdu systemesans travail du sol (No-Till) sur 1'infiltrationde l'eau et les parametres relies au sol ont ete etudies dans cinqchamps de terre ferme dans le sud de la Saskatchewan. Un simulateurde pluie a ete utilise pour mesurer Tinfiltration. Trois champs ont etesoumis au systeme de labourage sans travail pour differentes peri-odes de temps variant entre 5 et 13 ans. Deux champs ont ete soumisau labourage conventionnel utilisant une culture "heavy duty"; unsysteme appliquant une culture en continu dans un champs et unerotation traditionnelle en jachere du ble dans l'autre. Des contenus enmatieres organiques, des macroporosites ainsi que des conductiviteshydrauliques plus eleves ont ete obtenus dans les champs soumis ausysteme sans travail du sol, compares aux systemes plus convention-nels. Depuis la derniere culture conventionnelle sous rotation enjachere, la matiere organique dans les champs sans travail du sol etconventionnel avec culture en continu a augmente de 0.2% chaqueannee. Les plus faibles taux d'infiltration de pluie ont ete observesdans le champs conventionnel en jachere tandis que les taux d'infil-tration les plus eleves ont ete notes dans le champs avec culture encontinu, bien que non-significativement differents de ceux observespour le champs sans travail apres 13 ans. L'infiltration cumulative a60 minutes obtenue la meilleure correlation avec le contenu en

matiere organique; 1'infiltration cumulative a augmente de 9 mmpour chaque augmentation de 1% en matiere organique.

INTRODUCTION

Water infiltration into a soil is a complex and dynamic process governed by both surface and profile properties, some ofwhich are a function of time since the commencement of the

infiltration event. Tillage alters the porosity, the pore sizedistribution, and pore continuity of the soil profile near thesurface and thus has a major effect upon infiltrability. Thereplacement of conventional tillage with a system that disturbs only a limited fraction of the soil surface once a yearcan thus be expected to alter the infiltrability. The use of anytillage system that reduces the number of operations thatdisturb the soil results in higher soil organic matter content(Dick and Daniel 1987) and more surface residue (Tanaka1989; Edwards 1991). Straw residue reduces the effect ofraindrop impact upon aggregate disruption, while increasedsoil organic matter helps to strengthen soil aggregates(Wischmeier and Mannering 1969). These factors prevent theformation of a surface seal and will help to maintain highinfiltration rates (Lindstrom and Onstad 1984). No-till orzero-till may be defined as a crop management system inwhich the only soil disturbance is that necessary for simultaneous placement of seed and fertilizer (Coutts and Smith1991). No-till can increase the infiltrability through maintaining a higher macroporosity (Logsdon et al. 1990; Dunnand Phillips 1991; Edwards 1991) and more continuousmacropores with depth (Logsdon et al. 1990). Conventionaltillage will shear off any macropores developed during thegrowing season, thus limiting the continuity between thetilled layer and the subsoil. Dunn and Phillips (1991) foundthat soil pores of diameter 0.21 mm and larger are responsiblefor 70 to 80% of saturated water flow.

Although there are numerous studies reporting that no-tillresults in higher infiltration rates than conventional tillage,other studies have reported no effect or lower infiltrationrates (Baker 1987; Chang and Lindwall 1989; Mohamoud etal. 1990). These conflicting results may be related to type ofconventional tillage system and the type of the infiltrationtest, as well as to temporal changes in surface detention andmacroporosity that occur after tillage operations (Baker1987).

Of the various tillage systems presently in use in thesemi-arid Great Plains and Canadian Prairies, no-till has thebest potential of conserving soil and water and curtailingsalinization. For the Great Plains region of the USA or theCanadian Prairies, slightly higher spring soil moisture contents in the upper 300 mm with no-till as compared toconventional tillage have been reported (Tanaka 1989; Care-foot et al. 1990). This can be attributed to any or all of thefollowing: increased snow trapping, increased snowmelt infiltration, and decreased evaporation due to a greater residue

CANADIAN AGRICULTURAL ENGINEERING Vol. 35, No. 3, July/August/September 1993 165

coverage and less soil disturbance (Carefoot et al. 1990).The main objective of this project was to compare the soil

infiltrability of fields under a no-till continuous croppingsystem to fields under conventional tillage (with a heavy dutycultivator). Soil properties that can affect infiltration (bulkdensity, texture, organic matter content, macroporosity, antecedent moisture, saturated hydraulic conductivity) and theamount of straw residue were also measured. The type oftillage system can have an immediate effect on bulk densityand macroporosity and with time can affect organic mattercontent. Antecedent moisture content can be affected byslope exposure and position, crop type, and possibly thetillage system. Thus, the proper evaluation of infiltrationdifferences between tillage systems should ensure that neither texture nor antecedent water content be the main

contributor to these differences. Explanation of infiltrationdifferences can thus focus upon the possible role that tillagesystems have upon modification of the soil physical properties that influence infiltrability.

MATERIALS AND METHODS

Site and tillage system descriptions

The project was carried out on five different fields located 13km to the south of the town of Indian Head, SK (50° 32' N,103° 40' W). The town of Indian Head receives on average175 mm of precipitation during the growing season and 427mm annually. The averageannualair temperature is 2°C.

The five fields were located within 3 km of each other.

Their soils, sandy loam to loam in texture and formed fromtill materials, are classified as Black Chernozems, mainlyorthic Oxbow soils, with calcareous soils on knolls and upperslopes (Saskatchewan Soil Survey 1986). All fields were

Table I: Summary of tillage systems and crops for fields investigated in study

gently to roughly undulating with slight slopes (2-5%) risingto a maximum of 1 to 3 m above low spots.

Tillage and cropping operations on the five fields aredescribed in Table I. The farm operating size of these fieldswas between 50 and 100 ha in size. All crops during the studyperiod were in spring wheat. The Robbin and Biggar varietieshave much shorter stems than the Columbus variety plantedon the conventionally tilled (CT) field. No-till (NT) fieldsNT5 and NT13 were adjacent to each other. Fields NT10 andCT were adjacent and located about 3 km south of NT5 andNT13. The summerfallow (SF) field was located betweenthese two sets of fields. Rainfall infiltration measurements

were done during the first two weeks of August, 1991; soilsamples for later analysis were taken during September,1991; and single ring infiltration tests for steady-state infiltrability were done during the first week of October, 1991.The SF field, by the time the infiltration measurements weretaken in August, had already been cultivated twice for weedcontrol.

Field measurements

The approximate location of three infiltration sites within athree to five hectare area of each field was randomly chosenwith the limitation that the sites in any one field were to beno closer than 50 m and no further than 200 m distance from

each other. To minimize intersite effects of topography andslope position, all the sites were established at midslopepositions with slopes of one to three percent with the plantingdirection running downslope. At each site, one plot 1.0 mwide by 1.5 m long was prepared for a rain infiltrationmeasurement. Antecedent soil moisture samples were takenoutside the plot before the commencement of the infiltrationtest.

Field Tillage Crop Crop Years of Comments on tillage systemsystem previous to during study continuous

study year year cropping

SF conventional;

wheat-fallow

2 yr rotation

spring wheat fallow 0 Heavy duty cultivator; Fall

tillage; 4-6 fallow tillageoperations for weed control.

CT conventional; spring wheat, spring wheat, 9 Heavy duty cultivator for seedcontinuous wheat Columbus var. Columbus var. bed preparation; Seeding with hoe

NT5

NT10

NT13

166

no-till; flax

continuous cropping

no-till; canola

continuous cropping

no-till; canola

continuous cropping

spring wheat,Robbin var.

spring wheat,Biggar var.

spring wheat,Biggar var.

10

13

press drill; Straw spreader used;Stubble left over winter.

Hoe type no-till air seeder;2 narrow knife openers, one

for seed, another for fertilizer

(Conserva-Pak™ System)

Conserva-Pak™ System

Conserva-Pak™ System

MAULE and REED

A rainfall simulator similar to that of Meyer and Harmon(1979) was used to apply water. The simulator had twooscillating VeeJet nozzles (80100) held by an aluminumframe suspended 3.0 m above the ground. The rainfall occurred over a 1.6 m x 2.3 m area on the ground, butinfiltration was determined from a 1.5 m2 area directly underthe simulator. The 1.5 m2 plot area was hydrologically isolated by pushing steel siding 30 to 50 mm into the ground,with the long axis of the infiltration plot orientated down theslope. A steel apron at the lower end of the plot enabledcollection of runoff waters and sediment. The crop inside theplot area was cut to a height of 100 mm, approximately thatleft by local swathers. Care was taken to remove the cut cropbut to not disturb the soil surface or the straw residue alreadyon the ground. Photos were taken of the surface after cropremoval for later residue cover analysis. The maximum rainfall intensity of the simulator (81 mm/hour as measured in the1.5 m area) was used so as to be able to determine infiltrability as soon as possible after the commencement of the test.The simulator was operated at each site until three consecutive measurements of runoff rate resulted in similar values,usually occurring after 60 to 90 minutes of rain. Water running off the plot was collected in 500 mL jars at 2, 5, 10, 15,25, 35, and 45 minutes and every 15 minutes thereafter. Thesediment in the jar was dried and weighed to determinesediment runoff concentrations. The rate at which the jarsfilled was used to determine the runoff rate. The infiltration

rate was determined as the difference between the rainfall and

runoff rates with correction for sediment volume. All infiltra

tion measurements took place during the first two weeks ofAugust. No rainfall occurred during this period. Final(steady-state) infiltration rates were averaged from the lastthree readings.

A single ring infiltrometer was used to obtain an estimateof steady state infiltrability of the soils under ponded conditions. In October 1991, one measurement was taken per siteon the same plots upon which the rainfall infiltration measurements were conducted. Water was ponded in 200 mmdiameter aluminum cylinders driven 50 mm into the soil. A30 mm thick furnace filter was cut and placed on top of thesoil surface to minimize surface seal formation. The cylinders were filled with 150 mm of water twice and the rate of

water entry was calculated from the rate that the water surfacedropped within two hours after the second filling. Measurements obtained via this method were considered to be

'estimates' only, due to the variable hydraulic head of waterand due to the wetting front spreading that occurred with theuse of a single ring.

Percent residue coverage was estimated from the photographs. The number of times the points of a grid placed onthe photograph intersected a piece of straw, divided by thetotal number of grid points multiplied by 100 gave the percent cover. Antecedent soil moisture was determined from

three 300 mm deep samples taken adjacent to the infiltrationplot with an Oakfield sampler and bagged in 100 mm increments to later determine gravimetric soil moisture content.

Laboratory analysis

At the end of September, undisturbed soil cores, 100 mmlong and 82 mm in diameter were taken to a depth of 300 mm

from each of the infiltration plots. The cores were obtainedby pressing a 300 mm metal core with a cutting edge into thesoil. Three 100 mm long plastic sleeves inside the metal corercontained the soil.

Macroporosity in this paper is defined as the differencebetween the saturated volumetric water content and the water

content at a potential of 1.5 kPa. According to Hillel (1980)the equivalent pore diameter is 0.21 mm. The cores weresaturated by wetting from the bottom with a solution of0.005M CaS04, weighed for determination of saturatedwater content and placed on a coarse silt bed and subjected toa tension of 1.5 kPa by using a hanging water column (Klute1986).

Saturated hydraulic conductivity was measured from the100 mm cores after the retention measurements. A fallinghead permeameter was used for most samples except forthose with conductivities greater than 5.0 x 10" m#s" , wherea constant head device was used (Klute and Dirksen 1986).

Sand, silt, and clay contents were determined with themodified pipette method (Indorante et al. 1990), with nopretreatment for organic matter or carbonates. The organicmatter content of the surface 80 mm was determined by wetcombustion (McKeague 1978).

Statistical analysis

Due to time and budget constraints of the project, only threereplicates of infiltration measurements per field during midsummer were possible. Operation of the rainfall simulatorand site preparation took two persons and two trucks, one ofthem being a water truck. On a normal day of operation, itwas possible to only perform two rainfall infiltration tests.Given that only three replicates per field could be obtained, arigorous statistical comparison between tillage systems is notattempted; however, basic statistical tests of comparison andsimple regression were used to test for differences or relationships at the 0.05 level of probability (Steel and Torrie1980). As the summer fallow field was cultivated numeroustimes throughout the summer and lacked a crop, tests ofcomparison of means were done on only two sets; all thefields and just the cropped fields. Any statistically significantor observed differences between fields cannot thus be taken

as conclusive for this study, but should be taken as indicativeof possible trends to be followed up by more specificallydirected research.

RESULTS

Rain infiltration rates between fields showed the greatestdifferences between 15 and 60 minutes after the onset of

rainfall simulation, with the SF field being significantly different and lower than all the cropped fields and the NT 13 andCT fields being significantly different and greater than theNT5 field at 30 and 45 minutes (Fig. 1). Cumulative raininfiltration at 60 minutes summarizes the differences amongthe early infiltration rates; CT had the highest cumulativeinfiltration at 74 mm with the NT13 field the second highestat 69 mm. Of the cropped fields, NT5 had the lowest (TableII). None of these differences, however, were significant. Ofthe cropped fields, both the final rain and final ponded infiltration rates were the lowest for the CT field, althoughsignificant differences did not occur (Table II). The saturated

CANADIAN AGRICULTURAL ENGINEERING Vol. 35, No. 3, July/August/September 1993 167

25 T

-| 20

O

^ 15

Ico

£

10 ••

5-b

-H •4-

♦-—♦ Zero till- 5 yr♦ ♦ Zero till-10 yr» » Zero till-13 yr« o Conventional tillAr—• Summerfallow

... A

?N

-+- -+- -+-

20 40 GO 80 100

Time from commencement of rain (min)

—i

120

Fig. 1. Rainfall infiltration rate versus time since

commencement of water application. Any twopoints for the same time with similar letters arenot significantly different at a probability of 0.05.

hydraulic conductivities of the CT field also had lower valuesfor all depths than the other fields and were significantlydifferent from the NT5 and NT10 fields for the 0 to 100 mm

depth (Table II).Soil physical and hydraulic properties used in the interpre

tation of the infiltration measurements of the five fields tested

are summarized in Table III. Within the 0 to 200 mm depthintervals, the NT13 field had the highest values of sandcontent, bulk density, organic matter content, and macroporosity. In some cases the differences were significant. TheCT field had the lowest sand content, bulk density, andmacroporosity in the top 100 mm, being significantly different from the NT 13 field. Regression analysis of sand contentversus bulk densities of the surface 200 mm, for only thecropped fields showed a positive and significant relationship

7n

•

6-^^ •

# •

C 5-

••

O

2 4- **— • •

a> ii r^^£cd

EO 3- .^*^0*^ • •

i •'S>O 2-

= IIO

CO

1 -

0- 1 -1 1-0 5 10 15

Number of years since last conventional fallow-crop rotation

Fig. 2. Soil organic matter content versus number ofyears since conventional fallow-crop rotation.

(Table IV). Organic matter content was significantly relatedto the number of years since the last conventional crop-fallowrotation (Fig. 2), with the organic matter content increasingby 0.18 percentage points per year (Table IV). Organic mattercontent was not significantly related to texture or bulk density. As expected, the macroporosity of the SF field was highdue to recent tillage. Considering the cropped fields only, thesand content of the upper 100 mm, but not the 100 mm to 200mm interval, was significantly and positively related tomacroporosity (Fig. 3, Fig. 4, Table IV). The CT field had themost straw residue (expressed as percent coverage), while theSF field had the least (Table II).

Antecedent soil water contents (the soil water content

Table II: Infiltration and hydraulic conductivity values of field sites

Property

Cumulative rain infil.

(mm at 60 min.)

Rain final infil. rate

(x 10"6 m/s)

Depth (mm) NT5

surface 55.8b

surface 13.2b

NT10 NT13 SF CT

63.2b 69.3b 38.0a 73.6b

13.0b 12.7b 3.8a 11.6b

Ponded final infil. rate surface 13.7a 16.7a 11.4a 8.6a

(x 10"6 m/s)

Sat. hydraulic 0-100 18.6a 16.4a 7.0bc 10.8c 3.1b

conductivity 100-200 7.5ab 20.3a 8.1ab 4.7b 4.6b

(x 10"6 m/s) 200-300 6.3a 6.6a 5.0a 7.5a 4.7a

Note; Each number is an average of 3 samples.Row numbers with similar subscript letter or letters are not significantly different at P = 0.05.

Ponded infiltration data for the SF field were not taken.

168 MAULE and REED

TableIII: Soil physical properties used for predictive parameters of infiltration

Property

Sand (%)

Clay (%)

Bulk density (Mg/m )

Macropores

(>0.20mmdia)

(% of total vol.)

Antecedent soil water

content (Mg/Mg)

Organic matter (%)

Straw residue

(% coverage)

Depth (mm)

0-100

100-200

200-300

0-100

100-200

200-300

0-100

100-200

200-300

0-100

100-200

0-100

100-200

200-300

NT5

52.6ab

43.6ab

43.5a

19.0ab

25.2a

28.6ab

1.19ab

1.36ab

1.42a

6.1b

4.3ab

3.0a

0.10a

0.11a

0.15a

0-100 3.8ab

surface 82ab

NT10

45.7ab

39.9b

38.1a

21.6a

27.7a

30.5a

1.13b

1.27b

1.40a

6.8abc

3.3b

2.4a '

0.12ab

0.16a

0.11a

4.8a

70c

NT13

57.9a

56.6a

49.9a

15.5b

16.8b

19.1b

1.27a

1.48a

1.42a

10.0a

6.0ab

3.8a

0.11a

0.11a

0.12a

5.1a

77bc

Note; Each numberis anaverage of 3 samples. Analysis is fromthe 82 mm diameter soil cores.Row numbers with similar subscript letteror letters are not significantly different atP=0.05.

14 T

0

E

§

"6 8 +

ioQ.

28

12

10 "

6 «-

4 «•

2 "

30

A Zero till-5 yrO Zero till-10 yr♦ Zero till-13 yr* Conventional till

H

60

14 T

(D

E

liotCO

12 "

*- 8 -»

8oQ.

2

6 ••

4 •-

2 "

A Zero till - 5 yrO Zerotill-10yr♦ Zerotill-13yr• Conventional till

SF CT

46.7ab 44.1b

47.2ab 44.4ab

46.9a 49.9a

21.3a 19.4ab

23.6ab 23.5ab

24.6ab 23.7ab

1.17ab 1.10b

1.14b 1.33ab

1.43a 1.36a

9.5aC 4.0b

8.5a 4.5ab

4.5a 3.6a

0.16b 0.15b

0.18a 0.13a

0.18a 0.11a

2.7b 4.4ab

26d 86a

I I

40 50

Sand content (%)

Fig. 3. Macroporosity versus sand content for the 0 to100 mm depth intervals for the cropped fields only.

Sand content (%)

Fig. 4. Macroporosity versus sand content for the 100 to200 mm depth intervals for the cropped fields only.

CANADIAN AGRICULTURAL ENGINEERING Vol. 35, No. 3, July/August/September 1993 169

present at the start of the rain infiltration measurements) weresimilar among the no-till fields, whereas the SF and CT fieldswere significantly different and had more moisture in the top100 mm (Table III). Below the 100 mm depth, there was nosignificant moisture difference among fields, although the SFsoil moistures were numerically greater than the other fields.

DISCUSSION

Of the soil properties regressed against infiltration, soil organic matter had the strongest and most consistentrelationship with infiltration, regardless of whether the SFfield was (Table V) or was not (Table VI) included with thecropped fields. Considering the five fields together, for every1% increase in organic matter, the cumulative infiltration at60 minutes increased by 9.4 mm (Table IV, Fig. 5). Percentage sand and bulk density were not significantly related forany of the infiltration rates. Antecedent soil water was significantly and positively related when just the cropped fieldswere considered (Table VI). The 60 minute cumulative infiltration was the highest for the CT field and the lowest for theNT5; however, these two fields had the highest and lowestantecedent moisture contents, respectively, in the surface 100mm. This relationship was reverse to that expected; the

Table IV: Linear regression equations of soil parameters relevant to infiltration

higher the antecedent soil water content, the lower the initialinfiltration rates should be (Hillel 1980). It is possible thatprofilediscontinuities, textural differences, the type of tillagesystem, or residue coverage were confounding the effect thatantecedent moisture had upon the infiltration rates.

The high cumulative 60 minute infiltration of the CT fieldcould be due to the high residue coverage of this field whichprovided a better protection of the soil surface against sealformation from raindrop impact. The high cumulative 60minute infiltration of the NT13 field could be due to severalfactors: higher organic matter content and the tillage systemwhich both may lead to greater macroporosity, or the greatersand content. Without further investigation, the factors controlling infiltration for these fields cannot be further clarified.

Final infiltration rates reflect the soil layer with the lowestsaturated hydraulic conductivity, be that a surface seal or asub-layer. Ponded final infiltration rates are more representative of subsoil conditions, whereas raindrops are morethan likely to create a surface seal on bare soils (Hillel 1980).Given the high macroporosity, sand content, and organicmatter of the NT13 field relative to the CT, NT5, and NT10fields, it would be expected that the NT13 field would havehigher final infiltration rates and higher Ks values (Table II).

Independent variable Depth (mm) Dependent variable Slope Intercept n r P

Bulk density (Mg/m3) 0-100 Sand (%) 0.0067 0.838 12 0.60 <0.05

Bulk density (Mg/m3) 100-200 Sand (%) 0.0068 1.048 12 0.69 <0.05

Macroporosity (%) 0-100 Sand (%) 0.20 -3.42 12 0.63 <0.05

Macroporosity (%) 100-200 Sand (%) 0.10 -0.27 12 0.50 >0.05

Organic matter (%) 0-100 No. of years since

last conv. fallow

2.80 0.18 15 0.71 <0.01

C60 (mm) 0-100 Organic matter (%) 9.4 20.4 15 0.80 <0.01

n = numberof individualsin analysis;where n is only 12 individuals, only the cropped fields were included in the analysis, r = correlationcoefficient. P = significance level of correlation coefficient.C60 = cumulative infiltration at 60 minutes.

Table V: Correlation coefficients relating infiltration of all fields to soil physical properties (0 to 100 mm) and strawresidue cover

Dependent variable

Independent Sand Bulk Organic Sat. hydraulic Macro Antece. Straw

variable density matter

content

cond. porosity moisture residue

cover

i25 0.10 0.16 0.78* -0.40 -0.42 -0.13 0.78*

i35 0.06 0.14 0.77* -0.37 -0.43 -0.24 0.77*

i45 0.08 0.19 0.84* -0.33 -0.39 -0.14 0.69*

i60 0.02 0.14 0.78* -0.30 -0.56* 0.01 0.68*

i75 0.14 0.18 0.78* -0.11 -0.50 -0.16 0.74*

C60 0.08 0.18 0.80* -0.39 -0.45 -0.10 0.75*

i25 = infiltrability at 25 minutes, etc. C60 = cumulative infiltration at 60 minutes.*r value is significant at probability of 0.05.

170 MAULE and REED

Table VI: Correlation coefficients relating infiltration of cropped fields only to soil physical properties (0 to 100 mm)and straw residue cover

Dependent variable

Independent Sand Bulk Organic Sat. hydraulic Macro Antece. Straw

variable density matter

content

cond. porosity moisture residue

cover

i25 -0.07 -0.10 0.53 -0.77* -0.27 0.54 0.38

i35 -0.23 -0.20 0.52 -0.85* -0.23 0.62* 0.19

i45 -0.13 -0.06 0.67* -0.68* -0.20 0.57 0.05

i60 -0.01 -0.16 0.64* -0.54 -0.49 0.63* 0.07

175 0.06 -0.10 0.70* -0.22 -0.35 0.30 0.24

i90 -0.37 -0.27 0.48 0.10 -0.34 -0.02 -0.19

C60 -0.11 -0.09 0.59* -0.77* -0.30 0.59* 0.25

i25 = infiltrability at 25 minutes,etc. C60 = cumulative infiltration at 60 minutes.* r value is significant at probability of 0.05.

80

EE

cT 60.2.S

IEi§ 40

rE

o

s«3 20 +

-H

A Zero till-5 yr

O Zero till-10 yr* Zero till-13 yr

• Conventional till

D SurnmerfaHow

-+-

0 12 3 4 5 6 7

Organic matter content (%)

Fig. 5. Cumulative infiltration at 60 minutes versus soilorganic matter content..

Although the CT field had the highest cumulative infiltrationamount at 60 minutes, it did have the lowest final infiltrationand Ks values of the cropped fields. If these lower values arenot simply an artifact of chance due to the small sample size,they could be due to the lower macroporosity values and alsothe disruption of macropore continuity with the subsoil dueto more frequent tillage. Macropores, continuous between thesurface and subsurface horizons, result in increased flux ofwater to greater depths (Hamblin 1985; Logsdon et al. 1990;Edwards 1991). Conventional tillage results in the disruptionof continuous macropores formed by soil fauna, roots, orcracking (Hamblin 1985). Studies of macropore continuitywith dyes report that for CT fields no macropores were foundbelow a depth of 300 to 350 mm, whereas for NT fields dyedmacropores were found below these depths (Logsdon et al.1990). The low infiltration rates of the SF field can be explained by several factors: the possible development of asurface seal due to the lack of residue cover and a low soil

organic matter content; high antecedent moisture contents(Table III); and disruption of macropore continuity due tofrequent tillage.

Some of the differences in straw residue coverage betweenthe fields in crop (Table III) could be due to crop history. NT5was under flax the previous year, while NT10 and NT13 hadbeen under canola. The CT field, with the greatest coverage,had been under continuous Columbus wheat, a longerstemmed variety than the Robbin and Biggar varieties usedon the NT fields. These cropping practices could have resulted in the CT fields having organic matter levels consistentwith that of the NT fields (Fig. 2). A curvilinear fit betweenorganic matter content and the number of years since the lastconventional crop-fallow rotation (Eq. 1) suggests that apeakorganic matter content of 6.6% will be reached after 34 years.Natural grassland values from a site near the NT13 field hadan average organic matter content of 6.4% in the top 100 mm(Unpublished results, J. Schoenau, Saskatchewan Institute ofPedology, University of Saskatchewan, Saskatoon, SK).

om = 2.742 +0.227 Yr - 0.0033 Yr2 r = 0.71, P = 0.01 (1)where:

om - soil organic matter content in surface 80 mm (%),and

Yr = number of years since last conventional crop-fallowrotation.

The relationship between sand and macroporosity mightbe enhanced by organic matter contents or that of the tillagesystem; a 4% increase in sand content between sites in theNT5 field and sites in the NT13 field resulted in a doublingof the macroporosity (Fig. 3); a CT site with a sand contentof 59% had a macroporosity one-third that of a NT 13 fieldwith an equivalent sand content (Fig. 3). The increase inmacropores in no-till fields relative to conventional tilledfields has been observed by others (Logsdon et al. 1990;Dunn and Phillips 1991; Edwards 1991); however, Dunn andPhillips (1991) reported that for one year a conventionallytilled field had a greater amount of macropores. Severalstudies reported that no-till had lower or similar macroporosities than conventional tillage; however, this could bedue to several reasons: samples were obtained soon after thetillage operation (Lindstrom and Onstad 1984); the conven-

CANADIAN AGRICULTURAL ENGINEERING Vol. 35, No. 3, July/August/September 1993 171

tional tillage method used was moldboard plowing (Unger1992); or the macropores were defined with a numericallylarger potential (20 kPa as used by Chang and Lindwall1989).

Published studies of the effect of no-till upon infiltrationare varied in their findings. When the infiltration measurements are made immediately after a conventional tillageoperation, whether moldboard or chisel plow, the conventional tillage system usually results in higher infiltration ratesthan the no-till system because of greater porosity and greatersurface detention (Lindstrom and Onstad 1984; Baker 1987;Unger 1992). If the measurements are made several weeksafter the last tillage operation or if natural rainfall is used toobtain the measurements then the no-till system usually results in higher infiltration rates (Baker 1987; Chang andLindwall 1989; Mohamoud et al. 1990). Recently disturbedsoils have a greater capacity to accept water; however, thiseffect is not lasting as one heavy rain can reduce this capacity(Unger 1992).

Given that only three samples per field were taken, it isdifficult to verify trends or differences within and betweentypes of tillage, especially where textural variations occur.Texture appears to have a strong influence upon some of thesoil properties between fields; the field under no-till thelongest, NT13, had the greatest bulk densities, the highestmacroporosity, and the highest infiltration rates for the NTfields; all of these results could be explained either by highsand contents (Hausenbuiller 1978; Hillel 1980) or by no-tilleffects. Consideration of individual site values, and the relationship of other properties, indicates that other variableshave a confounding effect upon infiltration: organic mattercontent was not significantly correlated with sand or claycontent, but rather with number of years of no-till (Table IV);and infiltration was best correlated with organic matter (Fig.5) and not with texture.

CONCLUSIONS

From the results presented in this study several tentativeconclusions concerning the effects of no-till and conventional tillage systems upon water infiltration and related soilproperties may be arrived at. The conclusions are deemedtentative due to the limited number of field replicates (moresamples would have been better, but not possible due tolimitations). The information provided here, however, can beof use in helping to indicate possible trends and the directionof future, more specific, studies.

1. Early infiltration rates (during first 60 minutes of infiltration) were not significantly different between the no-tillfields and the continuously cropped conventional-tilledfield. The NT13 field and the CT field had both the

greatest and similar cumulative infiltration at 60 minutesdespite that sand content, bulk density, macroporosity,antecedent moisture content, and straw residue coveragewere all significantly different.

2. Cumulative infiltration after 60 minutes of simulated

rainfall was significantly correlated to organic mattercontent. The organic matter content was significantlycorrelated to the number of years since a conventionalfallow-crop rotation.

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3. Final infiltration rates for the cropped fields showed nosignificant difference between no-till and conventionaltillage systems, although the conventional field had thelowest values. No-till fields had saturated hydraulic conductivities in the upper 200 mm significantly different andgreater than that of the cropped conventional tillage system.

ACKNOWLEDGEMENTS

The authors thank J. Halford of Vale Farms Ltd. for field

access and information about his no-till system and D. Bayneof the Division of Hydrology, University of Saskatchewan,for field and laboratory assistance. This project was fundedwith a research contract from the Environmental Sustainabil-

ity Initiative of Agriculture Canada.

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