Soil & Tillage Research, 22 ( 1992 ) 383-389 383 Elsevier Science Publ ishers B.V., Ams te rdam

Short Communication

Effects of tillage and crop rotation on physical properties of a loam soil*

C. Chang and C.W. Lindwall Research Station, Agriculture Canada, P.O. Box 3000, Main, Lethbridge, Alta., T1J 4B1, Canada

(Accepted 2 April 1991 )

ABSTRACT

Chang, C. and Lindwall, C.W., 1992. Effects of tillage and crop rotation on physical properties of a loam soil. Soil TillageRes., 22: 383-389.

Advances in the development of non-residual herbicides have increased the interest in min imum tillage systems as an alternative to conventional cultivation. This study compared the effects of con- ventional tillage (CT), min imum tillage (MT) and zero-till (ZT) with continuous winter wheat, winter wheat-summerfallow, and winter wheat-barley-summerfallow on various properties of a Brown Chernozemic loam. Saturated hydraulic conductivity (HC), soil moisture retention, bulk density (BD) and infiltration rate of the soil were measured. The effects of crop rotation by tillage or crop rotation on these soil physical properties were not significant after 8 years of tillage. In general, the BD of the soil under ZT was greater than that under CT in the tillage zone and was lower below the tillage zone. The HC of ZT soil was less than that of CT soil in the tillage zone and greater below the tillage zone. Infiltration rates were not different among the tillage treatments. Although significant differences in some soil properties occurred among tillage treatments, these differences were likely to be too small to affect crop production.

INTRODUCTION

The traditional tillage and summerfallow-crop system is still the dominant cultural practice on the Canadian Prairies. However, Dormaar and Lindwall ( 1989 ) found a reduction in organic matter of cultivated soil under this sys- tem. Increased awareness of soil degradation resulting from wind and water erosion, soil compaction and soil salinity under present production systems has stimulated interest in developing alternatives. Research shows that min- imum and zero-till systems conserve more crop residual cover, reduce soil erosion losses (Hayes and Kimberlin, 1978 ) and save time and energy (Frye, 1985 ) without yield losses of cereal grains compared with conventional sys-

*Lethbridge Research Stat ion con t r ibu t ion No. 3878831.

© 1992 Elsevier Science Publ ishers B,V. All rights reserved 0167 -1987 /92 /$05 .00

384 C. CHANG AND C.W. LINDWALL

tems in southern Alberta (Lindwall and Anderson, 1981; Zentner et al., 1988; Carefoot et al., 1990) and elsewhere (Anderson, 1976; Unger and Wiese, 1979). Some soil physical properties that affect crop production may be fa- vourably or unfavourably modified by tillage (Douglas et al., 1979; Ghuman and Lal, 1984; Pagliai et al., 1984; Cassel and Nelson, 1985) depending on soil type, type of tillage equipment, tillage depth, soil conditions such as mois- ture content at the time of tillage and climatic conditions. Long-term studies indicated that the effects of various tillage and crop rotation systems on some properties of a southern Alberta clay loam were similar (Chang and Lindwall, 1989, 1990). If m in im um and zero-till systems are to be adopted as alterna- tive tillage systems to control soil erosion and improve soil and water conser- vation, it is necessary to examine their long-term effects on soil physical prop- erties and potential implications for crop growth.

The objective of this study was to compare the effects of conventional til- lage, min imum tillage, and no-till with continuous winter wheat, winter wheat- summerfallow and winter wheat-barley-summerfallow on hydraulic conduc- tivity, soil moisture retention, bulk density and infiltration rate of the surface 120 m m of soil to appraise these cultural practices.

MATERIALS AND METHODS

The plots were established in 1980 on a Brown Chernozemic loam at Vaux- hall, Alberta with crop rotations as main plots and tillage treatments as sub- plots in a split-plot design. Subplots were 6 m X 40 m. Particle size distribu- tion in the study area among 0-30, 30-60, 60-90 and 90-120-mm depth intervals was uniform and the mean contents of sand and clay were 45.2% and 18.2%, respectively. Organic matter content of the soil was 1.71%. The climate in the region is continental, cold in the winter (mean temperature of - 6 . 8 ° C in January) and hot in the summer (mean temperature of 18.5 °C in July). The long-term mean precipitation for this area was 330 m m year -~ (63% during May to September) which was about 70 m m less than that of Lethbridge, Alberta. The tillage treatments were conventional tillage (CT), min imum till (MT), and zero-till (ZT) and three winter wheat rotations were established: continuous winter wheat (WW), winter wheat-summerfallow (WF), and winter wheat-barley-summerfallow (WBF).

The CT treatment (tilled to a depth of 90 m m or less) utilized in the WF and WBF rotations was a wide-blade cultivator with 1520-ram sweeps for weed control during the summerfallow season (usually 4-5 times from May to September). The CT treatment in the WW rotation involved a double- offset disc or one-way disc for crop residue incorporation 1-2 weeks after harvest. The MT treatment in the WF and WBF rotations utilized appropri- ate rates of herbicides for broad-spectrum control of weeds and volunteer grain from May to July, and one tillage operation with the wide-blade cultivator in

T1LLAGE AND CROP ROTATION EFFECT ON LOAM SOIL 3 8 5

August. In both CT and MT treatments of all three rotations, the heavy-duty cultivator with 400-mm sweeps was used for initial seedbed preparation. A rod-weeder and packer combinat ion was used for final seedbed preparation. The ZT t rea tment in all rotations utilized herbicides for control of weeds throughout the fallow season and just prior to seeding. In all treatments, a high-clearance hoe press drill was used to seed winter wheat ( Triticum aesti- vum, cv. 'Norstar ' ) at 67 kg h a - ~ and barley (Hordeum vulgate, cv. 'Gait ' ) at 45 kg ha-~ on a 203-mm row spacing. Fertilizer was applied in a proper amount at appropriate times.

Two undisturbed soil cores (53.5 m m in diameter) were collected at depth intervals of 0-30, 30-60, 60-90 and 90-120 m m from each plot of three rep- licates in all t reatments in 1988 after harvest. Obvious wheel track areas were avoided. Soil bulk density (BD), water retention at moisture potentials of 0 (SAT), - 1 0 (MC10) , - 2 0 (MC20) , - 3 0 (MC30) , - 7 5 (MC75) , - 5 0 0 (MC500) and - 1500 ( M C I 5 0 0 ) kPa by pressure plate (Klute, 1986), par- ticle size distributions (Gee and Bauder, 1986) and saturated hydraulic con- ductivity (HC) (Sommerfeldt et al., 1984) were determined in the labora- tory. A separate sample was taken from 0-12 cm depth interval at each plot for analysis of water-stable aggregates (Kemper and Rosenau, 1986 ). Infiltra- tion rate was measured at all the winter wheat plots with the CT and ZT treat- ments using a single-ring infi l trometer (Bertrand, 1965 ). The soil in the ring was flooded initially with a predetermined amount of water and a constant head of 25-35 m m water was maintained during the infiltration measurement.

Analyses of variance were performed on all data. Tillage and crop rotation effects on the properties were tested with an orthogonal contrast test to assess the significance among t reatments (SAS Institute, 1985 ).

RESULTS

The analysis of variance indicated that the tillage by crop rotation interac- tion was not significant. Therefore, tillage and crop rotation effects on soil physical properties could be considered separately. The effects of crop rota- tion on soil properties were insignificant. Thus, all the data were pooled for analysis of tillage effect.

The effects of tillage t rea tment on the soil properties measured were vari- able depending on the depth intervals (Table 1 ). Soil bulk density of ZT at 0 -30 -mm depth was significantly lower than that of MT, and water retention of ZT at potentials of - 75, - 500 and - 1500 kPa was significantly higher than in CT and MT. At Depth 2 (30-60 m m ) , the HC of CT was higher than that of MT and ZT. However, the bulk density and water retention of ZT at

- - 1500 kPa were greater than that of CT. The water contents at potentials of - 2 0 , - 3 0 and - 7 5 kPa o f Depth 3 (60-90 m m ) of ZT were lower than those of CT, but HC and BD were not different. The HC was higher and bulk

386

T A B L E 1

M e a n v a l u e s o f so i l p h y s i c a l p r o p e r t i e s for t h r ee c r o p r o t a t i o n s

C. C H A N G AND C.W. LINDWALL

Ti l l age ~ S a t u r a t e d B u l k d e n s i t y h y d r a u l i c ( M g m -3 )

c o n d u c t i v i t y ( m s - ' )

V o l u m e t r i c m o i s t u r e c o n t e n t a t k P a

0 - 1 0 - 2 0 - 3 0 - 7 5 - 5 0 0 - 1 5 0 0

Depth 1 (0-30 mm) C T 12 .36X 10 -62a 1.21 ab 52.7 a 33.2" 24.6" 20 .4 a 15.6 a 11.2 a 9.2" M T 10 .61X 10 -6a 1.26" 51.3" 32.5" 24.7 a 20.7 a 16.2" 11.9" 10.0" Z T 1 0 . 3 1 × 1 0 -6" 1.17 b 52.4" 34.2" 25.8" 21.3" 17.4 b 13.2 b 11.2 b

Depth 2 (30-60 rnm) C T 1 5 . 8 9 × 10 -6a 1.29 a 49.1 a 30.7" 23.4" 20.2" 16.4" 12.2 a 9.8" M T 9 . 5 3 X 10 -6b 1.35 "b 48.7" 30.1" 23.3" 20.5 a 16.9 a 12.5" 10.5 "b Z T 5.67)< 10 -6b 1.39 b 48.1" 31 .0 a 23 .4 a 20.2 a 17.3 a 12.5 a 10.8 b

Depth 3 (60-90 rnm) C T 4 . 9 3 X 10 TM 1.43" 46 .6 a 29.9" 23.9" 21.1 a 17.7" 13.2 ~ 10.9 ~ M T 4.33)< 10 TM 1.46" 45.4" 30.7 ~ 24 .0 a 20.7 a 17.3 ~ 13.3" 11.6 b Z T 5.19)< 10 -6a 1.44 ~ 45 .0 ~ 29.8" 22 .W 19.7 b 16.5 b 12.8 a 10.8"

Depth 4 (90-120 ram) C T 5 .46X 10 TM 1.44" 45.4" 30 .0 ~ 22.8 ~ 20.1 a 16.6 ~ 12.5 ~ 11.0" M T 6.28)< 10 TM 1.41 "b 47 .0 b 30.2 ~ 23.1" 20.3 a 16.6 ~ 12.2 ~ 10.7 a Z T 7.48>( l 0 -6b 1.39 b 47.8 b 30.3" 23 .2 ~ 20.5 ~ 16.8 ~ 12.8 ~ 11.0"

'CT, C o n v e n t i o n a l t i l lage; MT, m i n i m u m t i l lage; ZT, ze ro t i l lage . 2 W i t h i n e a c h c o l u m n for e a c h d e p t h i n t e rva l , v a l u e s w i t h t he s a m e s u p e r s c r i p t l e t t e r s a re no t s igni f i -

c a n t l y d i f f e r en t a t the 0.05 level .

80

6o

r ~

r- 40 0

~ 20

Conventional tillage Minimum tillage Zero till

0 I I I i I

0.1 0.1- 0.25- 0.15 - 1-2 2-5 >5 0.25 0.5 1

Aggregate size range (mm)

Fig . 1. D i s t r i b u t i o n o f w a t e r - s t a b l e a g g r e g a t e s i n t h e soi l .

I Total, Total,

<1 >_.1

density lower under ZT than under CT at Depth 4 (90-120 mm). The satu- ration percent of ZT and MT was higher than that of CT.

There were slightly more water-stable aggregates in the size ranges of 0.1-

TILLAGE AND CROP ROTATION EFFECT ON LOAM SOIL 3 8 7

0.25, 0.25-0.5 and 0.5-1.0 m m under CT and MT than under ZT at 0-120 m m depth. However, water-stable aggregates greater than I m m diameter were not different among the tillage treatments (Fig. 1 ). The steady infiltration rate in the 0 -120-mm depth interval, as measured by a single-ring infiltro- meter, was not different between CT and ZT and the mean infiltration rate was 3.55 X 10 - 6 m m s - ' . The water contents of the soil 24 h after infiltration also were not different between CT and ZT and the mean moisture was 19.0% by weight.

D I S C U S S I O N

The lack of significant crop rotation by tillage and crop rotation treatment effects on the soil physical properties could be due to the similarity of winter wheat and barley root systems. Tillage treatment effects on the SAT, HC, BD and water retention of soil were small and could be attributed to the fact that the depth of tillage in CT and MT treatments was only 90 m m or less. These findings also were supported by other studies on a clay loam soil in Leth- bridge, Alberta (Chang and Lindwall, 1989, 1990). The depth of conven- tional cultivation for dryland cereal production in southern Alberta is rela- tively shallow compared with elsewhere, where tillage may be to a depth of 200 m m (Van Doren et al., 1977).

The soil compaction problems due to machinery traffic reported by others (Campbell et al., 1974; NeSmith et al., 1987 ), where the soil was cultivated under semi-humid or humid climatic conditions, were not evident in this study. In our study, the average soil moisture content rarely approached - 2 0 kPa at the times of tillage and was usually in the range of - 100 to - 5 0 kPa. Compactibility is low in this moisture range (Larson et al., 1980). Even if the soil had been compacted by tillage, freezing and thawing cycles during the winter would have alleviated some of the effects (Wittsell and Hobbs, 1965; Larson and Allmaras, 1971 ).

Cycles of very cold periods followed by chinook warm spells are prevalent during the winter in southern Alberta (Grace, 1987 ). These conditions pro- duce frequent freezing and thawing cycles which could explain why measured physical properties of the surface 30 m m were virtually unaffected by tillage treatment, even under ZT conditions. Tillage with the heavy-duty cultivator should have loosened the soil, but the final seedbed preparation with the rod- weeder and packer combination may have re-compacted the surface soil layer. As a consequence, the bulk density of the surface layer of soil under CT was greater than that of soil from the ZT plots.

In conclusion, after 8 years of different treatments, including zero till, there were some small differences in some of the physical properties of this Brown Chernozemic loam. However, as indicated by the yield of winter wheat

388 C. CHANG AND C.W. LINDWALL

( C a r e f o o t e t a l . , 1 9 9 0 ) a n d o t h e r r e s e a r c h e r s ( L e t e y , 1985 ), t h e d i f f e r e n c e s w e r e t o o s m a l l t o a f f e c t c r o p p r o d u c t i o n a d v e r s e l y .

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