ROTATION AND TILLAGE EFFECTS ON AVAILABLE SOIL-WATER FOR WINTER-WHEATIN A SEMIARID ENVIRONMENT

The recent adoption of conservation farming systems in the semi-arid C anadian prairies opens up the possibility of replacing the traditional fallow period with non-cereal crops (oilseeds, legumes). However, inf ormation on changes to soil water regimes by inclusion of these crops, especially in combination with zero tillage, is sparse. A study was i nitiated in 1984 on a sandy clay loam soil at Lethbridge, Alberta, to investigate the performance of winter wheat (Triticum aestivum L.) und er conventional, minimum and zero tillage in monoculture and in 2-year rotations with fallow, canola (Brassica campestris L.) or lentils (Le ns culinaris Medic.) /flax (Linum usitatissimum L.). Conventional till age in the Lethbridge region is shallow cultivation (10 cm) with a wid e-blade (sweep) cultivator. Continuous cropping greatly depleted soil water reserves, resulting in some crop failures. Averaged over 10 year s, available water for establishment of winter wheat in fall was least after canola (45 mm), followed by continuous winter wheat (59 mm), le ntils/flax (74 mm) and fallow (137 mm). In this semi-arid region, the effect of rotation on soil water was much greater than that of tillage . Zero tillage had relatively little impact on available water to 1.5 m depth. However, once the experiment had been established for 6-7 yea rs, available water in the 0-15 cm depth under winter wheat in spring was greatest under zero tillage. Precipitation storage efficiency duri ng the fallow year was generally unaffected by tillage system.