Grazing and Tillage Effects on Soil Properties, Rain Infiltration, and Sediment Transport during Fallow

Depletion of the High Plains Aquifer that supplies irrigation water for the semiarid Southern Great Plains may necessitate dryland production of crops like wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] using the wheat-sorghum-fallow (WSF) rotation. Reduced crop productivity without irrigation can be offset by intensifying the WSF rotation with cattle (Bos taurus) grazing. Biomass removal and soil trampling without tillage, however, may reduce rain infiltration and storage during fallow that increases with no-tillage (NT) over stubble-mulch (SM) tillage. Our objective was to quantify grazing and tillage effects on infiltration, sediment transport, and aggregate stability during fallow periods after sorghum and wheat. Using a split plot randomized complete block design, we compared wet aggregate size distribution of a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll; 0.0-0.05 m) and sediment yield in runoff of simulated rain during the fallow-like idle period after wheat and the sorghum fallow. Sediment concentration and yield for both fallows were numerically larger (> 40%) with grazing. Sediment concentration from SM tillage increased significantly over NT for either fallow, but soil loss differed only for wheat fallow. Mean final infiltration rate (IRf) and amount (IA60) did not differ significantly with grazing during either fallow, but IA60 was usually 20% lower for grazed than for ungrazed paddocks. Because SM tillage after grazed wheat significantly (P < 0.01) increased IRf and IA60 over NT, occasional SM tillage to disrupt compaction from trampling may increase water conservation for dryland cropping systems combining grazing with NT residue management.