Relations between corn yield and rainfall and optimal irrigation date in north shaanxi and weibei plateau 渭北玉米降水产量关系与最佳补充灌溉时期初步研究
2.
Two aspects of the problem are discussed : one is that lift irrigation is no need when abstraction volume capability of canal head can meet the demand ; the other is that lift irrigation is in need when abstraction volume capability of canal head can not meet the demand 它包括两个方面：一是当渠首可引水量能满足灌区灌溉用水量时，则不需要提水灌溉；二是当渠首可引水量尚不能满足灌区灌溉用水量时，则需提水灌溉来补充灌溉用水量。
