Soil water accumulation under different precipitation, potential evaporation, and straw mulch conditions

Small precipitation amounts generally have low effectiveness for crop production in semiarid regions. Our objective was to determine potential evaporation (PE; 3, 6, or 12 mm d(-1)) and straw-mulch (0, 2, or 4 Mg ha(-1)) rate effects on water accumulation in Pullman (Torrertic Paleustoll, 37% clay) and Randall (Ustic Epiaquerts, 57% clay) soils when small amounts of water (simulated precipitation; 5, 10, or 20 mm) were applied. Water accumulation was affected in order by water-application amount > PE > mulch > soil clay content. Mulching at 2.0 and 4.0 Mg ha(-1) increased storage efficiency of 5-mm water applications by > 60 and 100%, respectively, in both soils when PE was 3 mm d(-1). With 5-mm water applications and 6 mm d(-1) PE, > 10% of applied water was stored in mulched soils, but not in bare soils. When PE was 12 mm d(-1) , little storage from 5-mm applications occurred in bare soils, but 3 to 6% storage occurred when the mulch rate was 4.0 Mg ha(-1). To obtain > 10% water storage when the PE rate was 12 mm d(-1), 10-mm water applications and a 2 Ms ha(-1) mulch rate were necessary, Evaporation rates were slightly higher for mulched soil than for bare soil in the late stage. Soil clay contents were correlated positively with accumulative evaporation in the late stage. Soil wetting depth increased with increases in mulch rates, Based on this study, straw mulching has potential for increasing soil water storage from small amounts of precipitation.