Aggregation of Soil Cropped to Dryland Wheat and Grain Sorghum

Abstract

AbstractSuccessful and sustainable semiarid dryland cropping depends on effective soil water storage and erosion control, which are influenced by surface soil aggregate size and stability. We hypothesized long‐term tillage and cropping system treatments affect water‐stable aggregate size distribution, aggregate water stability, and dry soil aggregation. A study on a Torrertic Paleustoll from 1982 to 1994 at Bushland, TX, involved tillage methods (no‐tillage, NT; stubble mulch tillage, SMT) and cropping systems for dryland winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] production. In 1994, mean percentages of >4‐mm water‐stable aggregates at 0 to 2 cm were 3.5 with NT and 1.0 with SMT in wheat, sorghum, fallow, rotation phase, or crop comparison plots. Mean percentages of <0.25‐mm aggregates were 49.0 with NT and 37.8 with SMT. More small aggregates with NT help explain why infiltration was 90% greater with SMT than with NT during fallow after sorghum and 26% greater with SMT during fallow after wheat in a similar study on the same soil when surface coverage by residues was limited (25% with SMT, 57% with NT for sorghum; 73% with SMT, 86% with NT for wheat). Aggregate sizes differed due to cropping system, rotation phase, and crop, but aggregate water stability and dry aggregation differences generally were nonsignificant. Both NT and SMT are deemed suitable for dryland crops under conditions as in this study because neither resulted in unfavorable soil conditions or major yield differences.