[en] The role of various factors in the soil-plant-atmosphere system in determining the water use efficiency of crops is examined. Possible ways of improving water use efficiency are indicated, with emphasis on modern views of soil-water availability to plants. Determination of the field water balance is shown as a necessary tool in crop water use research. Field techniques for measuring the water balance with the aid of neutron and gamma probes and other physical instrumentation are presented. Experiments being currently conducted at IARI are used to illustrate the outlined approach to water use efficiency research problems. (author)