LONG-TERM TILLAGE AND CROPPING SYSTEMS AFFECT BULK-DENSITY AND PENETRATION RESISTANCE OF SOIL CROPPED TO DRYLAND WHEAT AND GRAIN-SORGHUM

Stubble mulch tillage (SMT) and no-tillage (NT) are well adapted for d ryland crops in the US Great Plains. Long-term use of NT, however, may impair soil physical conditions and crop yields, and, by inference, s oil quality and production sustainability. We determined effects of us ing SMT and NT in several cropping systems for dryland winter wheat (T riticum aestivum L.) and grain sorghum (Sorghum bicolor (L.) Moench) p roduction on soil bulk density (BD), penetration resistance (PR), and water content (WC). We determined these in 1994 in plots of a tillage method and cropping system study started in 1982 on Pullman (Torrertic Paleustoll) clay loam at Bushland, TX, USA. Due to the nature of the study, a common statistical analysis of the data was not appropriate, but eight separate analyses were possible. Besides tillage method and cropping system, these allowed comparisons due to rotation phase, land condition (level or non-level), and crop grown. Soil ED and PR always increased with depth and WC often increased. The tillage x depth inte raction effect also was significant. Soil ED and PR were lower in the tillage layer (0-10 cm depth) in SMT than in NT plots, but no definite trends for ED were evident below 10 cm. Based on regression analyses, PR with SMT was related to ED and WC of the entire profile and most d epth increments. With NT, PR was related to profile ED and WC, but onl y to WC for individual depths. These results indicate some strength fa ctor largely independent of ED and affected by WC strongly influences PR of NT soil. Because NT does not disturb the soil, we concluded that stable biopores created by soil organisms and root channels reduced t he effects of ED differences among NT plots and that NT soils develope d a rigid structure independent of ED. Reports of improved trafficabil ity on NT soils support this conclusion. Results of this study and pre viously reported crop yields suggest long-term use of NT will not impa ir the quality and production sustainability of this and similar soils under dryland cropping conditions. Published by Elsevier Science B.V.