Abstract: Field water balance for corn, sorghum and soybean is estimated. The influence of four treatments on various components of water balance equation and on water regulation is studied. Crop growth, yield response and water use efficiency (WUE) under different treatments are analysed. Results show that the field water storage capacity in treatment of plowing with winter irrigation (P+WI) is higher than those of plowing without irrigation (CK), plowing with spring irrigation(P+SI) and subsoiling (35—40cm)with winter irrigation (SL+WI). Plowing with winter irrigation can increase about 100mm of available water within lm cinnamon soil profile, which accounts for two thirds of total available water capacity. It is enough for main crops to resist severe spring and summer droughts and to increase water use effeciency(WUE). Plowing with winter irrigation (P+WI) together with subsoiling(SL) at interval of two or three years is the best combined practice.

Key words: Water balance, Winter irrigation (WI), Spring irrigation(SI), Water use efficiency(WUE), Evapotranspiration(ETc)