Precipitation, runoff, and yields from terraced drylands with stubble‐mulch or no tillage1

Abstract Dryland crops rely on precipitation as their exclusive water source, but storm water runoff decreases the amount available for biomass and grain production. Management practices that minimize runoff often increase the opportunity time for infiltration and improve precipitation storage as soil water. Our objective was to quantify storm water runoff from contour farmed terraces in relation to precipitation and field characteristics and then relate runoff to soil water at planting and yields of wheat ( Triticum aestivum L.) and sorghum [ Sorghum bicolor (L.) Moench] grown in a 3‐yr wheat–sorghum–fallow (WSF) rotation. Comparisons of long‐term (1984–2010) runoff observations indicated mean annual runoff for both uncropped periods of the WSF rotation were significantly greater with no‐tillage (NT) than stubble‐mulch (SM) tillage. By contrast, soil loss was greater for SM than NT because residue cover of undisturbed NT soil was less subject to entrainment and loss. Increasing field slope from 1.2 to 1.8% produced greater fallow runoff, which is water lost from dryland production. Nevertheless, soil water was significantly greater with NT, which reduced evaporative losses during fallow compared with SM. Long‐term wheat yields exhibited no difference due to tillage, but NT grain sorghum yields increased significantly over SM tillage. The data show that while runoff with NT was typically greater than SM, profile soil water at planting was also greater for NT and increased grain sorghum yields significantly. We conclude that decreasing evaporative water losses with NT residues is the primary factor affecting soil water conservation.