Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/1996
Publication Date: N/A
Interpretive Summary: Soil moisture conservation is a critical issue in dryland, semiarid grain production systems of the Canadian Prairies. Reduced tillage systems, including no tillage, can be effective in reducing water loss from the soil by leaving a protective layer of crop residues on the soil surface to reduce evaporation. We hypothesized that the soil pore network would be altered with tillage such that rainfall might be better utilized by crops. Smaller, more effective pores for holding soil water occupied more of the soil volume under no tillage compared with soil under conventional tillage. Tillage loosened the soil, resulting in larger pores that drained freely with gravity, resulting in less water stored in the surface soil. The shearing action of tillage at a depth of 75 to 100 mm appeared to cause greater discontinuity of pores. Availability of soil water to crops was improved with no tillage due to improved water storage in smaller pores. Crops managed with no tillage in the cold, semiarid climate of the Canadian Prairies would appear to be better suited to tolerate water-limiting situations than crops managed with conventional tillage.
Technical Abstract: Tillage management can affect crop growth, in part by altering the pore structure and hydraulic properties of soil. We hypothesized that water retention, pore size distribution, and unsaturated hydraulic conductivity (k) differed under conventional tillage (CT) and no tillage (NT). We evaluated this hypothesis on a Donnelly silt loam (fine-loamy, mixed, frigid Typic Cryoboralf) and a Donnelly sandy loam (coarse-loamy, mixed, frigid Typic Cryoboralf) in northwestern Canada. Soil cores were collected from the 0 to 300 mm depth in 75 mm increments. Water retention was measured at ten pressure levels from -2 to -400 kPa to calculate pore size distribution and k. Both soils retained 0.04 to 0.09 m3/m3 more water under NT than under CT. The volume fraction of total porosity with pores <7.5 m in diameter (effective pores for retaining plant-available water) in the silt loam averaged 0.49 and 0.58 m3/m3 under CT and NT, respectively and in the sandy loam averaged 0.39 and 0.51 m3/m3 under CT and NT, respectively. Conventional tillage appeared more likely to interrupt capillaries than NT, since large differences in k between tillage regimes were observed below a depth of 75 mm with increasing moisture deficit.