CROP AND SOIL RESPONSE TO LONG-TERM TILLAGE PRACTICES IN THE NORTHERN GREAT-PLAINS

Summer fallow is the most common cultural practice in the northern Great Plains. With proper cultural management, however, annual cropping may be feasible and economical. Our objective was to determine crop and soil response to nontraditional annual cropping practices (till and no-till) in lieu of conventional fallow-crop rotation for the production of spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) in the northern Great Plains. The study, initiated in 1983, was on a Dooley sandy loam (fine-loamy, mixed Typic Argiboroll) 11 km north of Culbertson, MT. Tillage practices on annually cropped treatments included sweep tillage in autumn and disk tillage in spring; sweep tillage in spring; and no-tillage. Conventional fallow-spring wheat rotations were included as the control. With three exceptions, there were no statistical differences among treatments in soil P, soil nitrate N, and pH. Phosphorus and N were nonlimiting in all years; pH decreased about 0.06 units per year in the 0- to 8-cm layer because of N fertilization. Bulk density differences in the 0- to 10-cm layer appeared after 7 yr, with the lowest bulk density for the no-tillage annual crop treatment. Grain and straw yields with the no-tillage treatment were both 80% of yields with the fallow-crop treatment. Total water use efficiency, based on soil water differences between harvest of one crop and harvest of the next, was significantly greater with no-tillage than with the fallow-crop treatment. Soil organic C decreased nearly 0.4 g kg(-1) per year with the fallow-crop treatment; there was a negligible decline with the no-tillage annual crop treatment. No-tillage annual spring wheat crop production was the most efficient crop and soil management practice from the standpoint of yield, water use efficiency, soil organic C, and bulk density.