TILLAGE-STUBBLE EFFECTS ON OVERWINTER MOISTURE CONSERVATION IN THE SEMIARID, CHINOOK-DOMINATED AREA OF SOUTHERN ALBERTA

Soil moisture and microclimate were measured on plots with different t illage and stubble treatments during the fall-winter-spring period (19 86-1987 and 1987-1988) in the chinook-dominated environment of souther n Alberta. Crop residue of winter wheat was used in the surface treatm ents of tall-stubble, short-stubble, fall-bladed and fallow plots. In spring, soil moisture in the fallow plot was greater than in the fall- bladed and short-stubble plots. In contrast, the soil water recharge d uring winter was greatest in the tall-stubble plot and smallest in the fallow plot. The near-surface microclimates of the treatments changed with variations in snowfall accumulation and ablation. The ablation o f snow cover was greatest on the fallow plot and less on the fall-blad ed and short-stubble plots and least on tall-stubble. The ablation of snow and resulting evaporation, reduced the soil recharge potential of overwinter precipitation in the fallow plot. As the tall-stubble surf ace accumulated significantly more snowfall than the other surfaces, m ore energy was required for evaporation, sublimation and melting. Infi ltration of meltwater was important to the soil moisture reserve in th e unfrozen soil. Little change in soil moisture was observed while the soil profile was frozen.