Contrasting tillage effects on stored soil water, infiltration and evapotranspiration fluxes in a dryland rotation at two locations

Abstract

There are significant uncertainties in partitioning growing season precipitation into the water balance components that determine water available for dryland crop yield across a range of environments and tillage practices. We evaluated profile soil water contents at a high temporal resolution during phases of a dryland wheat (Triticum aestivum L.) –sorghum (Sorghum bicolor L.) -fallow rotation under no tillage (NT)1 and stubble-mulch tillage (ST) management at Bushland, Texas and Tribune, Kansas to assess event-based soil water balance components. Cumulative infiltration and evaporation were estimated based on hourly changes in stored soil water using a water balance approach and a drainage model. Estimated deep drainage comprised a small proportion of the soil water budget averaging five percent of annual precipitation in Bushland. Tillage did not significantly influence cumulative infiltration during summer fallow and growing season periods at Bushland. In contrast, NT at the Tribune location exhibited significantly greater (P = 0.023) cumulative infiltration compared to ST during the wheat fallow period just prior to sorghum planting. At both locations during summer fallow periods, NT was not more efficient in increasing stored soil water over that obtained with ST. Evaporation during summer fallow periods was more a function of the soil water content near the surface than the tillage practice. Effective infiltration expressed as a fraction of precipitation averaged 0.55 and 0.57 under NT and ST, respectively, at Bushland compared with 0.83 and 0.52 under NT and ST, respectively, at Tribune. Observations of effective infiltration elucidate historical results of the incremental sorghum grain yield response of NT over ST that averaged 12 percent at Bushland and 35 percent at Tribune. Partitioning of growing season precipitation to transpiration was insufficient in Bushland to generate yield increases under NT of similar magnitude to that observed in Tribune demonstrating that NT does not perform similarly across all environments.