ORGANIC-MATTER, NUTRIENT, AND PH DISTRIBUTION IN NO-TILLAGE AND CONVENTIONAL-TILLAGE SEMIARID SOILS

There is widespread interest concerning whether the influence of conservation tillage systems on soil conditions is beneficial or detrimental to crop production. Objectives of this study were to evaluate the distribution with depth of organic matter (OM), total N, NO3-N, P, K, Ca, and pH on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). The crop rotation used was dryland winter wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]-fallow (WSF) involving stubble mulch (SM) tillage and no-tillage (NT). The SM field and an adjacent NT field had been used for the WSF rotation since 1956. No-tillage was started on the adjacent field in 1981 (NT-81), continuing the same rotation. On another field, the NT-WSF rotation was started in 1979 (NT-79) on land previously used for irrigated crops. Sampling was in August 1988 at depths of 0 to 1, 1 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, 10 to 15, and 15 to 20 cm. On the SM field, there were few differences, except for pH, throughout the tillage zone (0-8 cm). There were differences at depths below 8 cm in some cases relative to those above 8 cm. The NT fields tended to have higher mean OM, N, NO3-N, P, and K values at the surface than the SM field, but all differences were not significant. In general, more differences with depth were significant on NT fields than on the SM field. Although NT is changing the distribution of OM and some plant nutrients in the soil, the changes are relatively small and NT appears to be a viable cropping practice for conserving soil and water and maintaining crop productivity on dryland in the southern Great Plains.