SOIL-STRUCTURE AND CROP YIELD OVER A 5-YEAR PERIOD FOLLOWING SUBSOILING SOLONETZIC AND CHERNOZEMIC SOILS IN SASKATCHEWAN

The effect of subsoiling of Solonetzic and of Chernozemic soils was studied over a 5-yr period under dryland conditions and under irrigation, involving 11 farm sites, and 2 soil zones. Subsoiling reduced soil density for up to 3 yr on most of the Solonetzic soils and on one of the Chernozemic soils. Over-winter soil-water recharge in subsoiled Solonetzic soils was increased for up to 3 yr, but not in subsoiled Chernozemic soils. Under irrigated conditions, subsoiling reduced soil salinity and sodicity at one site; however, under dryland conditions soil salinity and sodicity levels remained unaltered. Crop emergence on one of the Solonetzic soils was decreased in the first year after subsoiling because of poor seedbed conditions. Subsoiling increased crop production on Solonetzic soils in the 1st, 2nd, 3rd and in the 4th years, and at one site in the 5th year. Subsoiling did not affect crop production on Chernozemic soils. Increased crop production resulted from increased soil water depletion with depth, and also from greater crop water-use efficiency. Soil loosening by subsoiling, as indicated by decreased soil bulk density of the B horizon lasted up to 3 yr, during which the largest yield increases were measured. The results suggest that subsoiling may have to be repeated every 5 yr or more.