CONSERVATION TILLAGE FOR SPRING WHEAT PRODUCTION IN SEMIARID SASKATCHEWAN

In semi-arid Saskatchewan, the major incentives for adoption of conservation tillage are water and soil conservation. Zero and minimum tillage systems for spring wheat (Triticum aestivum L. or Triticum turgidum L.) grown continuously and on summer fallow were studied on sandy loam, silt loam, and clay soils between 1982 and 1988. Effects on water recharge, soil fertility, crop yields, and soil erosion risks were measured. Zero-tillage fallow reduced evaporative losses during dry summers and conserved 8% more spring soil water after 21 months compared with conventional fallow (232 mm vs. 214 mm) on the silt loam soil; minimum tillage fallow conservea an extra 3% spring soil water (225 vs. 214 mm). Soil nitrogen fertility under zero-tillage fallow was generally lower than under conventional tillage in the first years of the study, but these trends disappeared with time. Yields of spring wheat grown on fallow on the silt loam soil were greater with zero-tillage (1477 kg ha-1) compared with conventional tillage (1198 kg ha-1) in two dry years, lower in one year (1248 vs. 1558 kg ha-1, respectively), and otherwise equal (2725 kg ha-1 on average). Grain yields on minimum tillage fallow were generally equal to or lower than with zero tillage on all soil textures. When spring wheat was grown continuously, yields were similar whether sown directly in stubble or after preseeding tillage. Elimination of some or all tillage operations for fallow and prior to seeding sufficed to maintain the fraction of wind-erodible aggregates (diameter < 0.84 mm) below the 60% threshold value in most years on the silt loam and clay soils. Based on crop residue conservation and soil aggregation, only chemical fallow can ensure adequate wind erosion protection for coarse- or fine-textured soils in low wheat yield areas, while minimum tillage can provide sufficient wind erosion protection on a silt loam. © 1990.