Residue management and paratillage effects on some soil properties and rain infiltration

Dryland winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] are often grown on the semiarid North American Great Plains using the wheat-sorghum-fallow (WSF) crop rotation. When used with WSF, no-tillage (NT) and stubblemulch tillage (SM) residue management reduce evaporation and increase yield, but more runoff occurs with NT compared to SM. Our objectives were to determine the effects of NT and SM residue management with paratill (PT) and sweep (ST) tillage on soil properties and rain infiltration into a Pullman clay loam (US soil taxonomy: fine, mixed, superactive, thermic Torrertic Paleustoll). Six contour-farmed level-terraced watersheds were dryland cropped using a WSF rotation with each phase of the WSF appearing all years as main plots. Residue management by tillage subplots of: (i) NT with PT, (ii) NT with NOPT, (iii) NT with ST, (iv) SM with PT, and (v) SM with NOPT were installed within these main plots after sorghum harvest. Approximately, 9 months later during the wheat phase (before planting), we measured selected soil characteristics and the infiltration rate and amount using a rotating disk rain simulator that applied cistern stored rainwater at 48mmh-1 on the five tillage-residue management treatments. Cumulative infiltration at 1h was similar among tillage treatments within residue management practices, i.e., infiltration into SM plots averaged 32.4+/-3.9mm compared to 21.9+/-2.5mm for NT plots. Regardless of residue management, PT and ST tillage caused no significant (P<0.05) increase in infiltration compared to NOPT. Measured cone-penetrometer resistance, bulk density, and initial soil-water content decreased with ST and PT for NT residue management but not SM residue management. The data show that SM residue management compacted the soil beneath, the sweep implements; thus, negating any benefits of reduced soil bulk density and penetration resistance with PT. We conclude that reductions in soil density and penetration resistance due to PT were diminished by SM tillage and that infiltration was regulated at the soil surface by a rapidly forming crust, which negated PT effects on SM or NT.