Factors determining water use efficiency in aerobic rice

With shortages and increased cost of irrigation water in many rice growing areas, water saving technologies such as aerobic rice are required to ensure sustainable rice production. The present study is a review of published papers on aerobic rice which have shown a wide variation in water use efficiency (WUE, grain yield/water input) ranging 2-15 kg ha(-1) mm(-1) among the 41 cases examined, with a mean increase in WUE of more than 50% but 6% decrease in yield compared to flooded rice. There was a large variation in the proportion of water input that was lost as seepage and percolation, and low WUE in some experiments was obtained in frequent irrigation which was required to maintain growth in aerobic rice. Water saving in aerobic rice was greater during the early stage of growth when soil evaporation was still high. The use of plastic mulch and drip irrigation has helped increase WUE in aerobic rice. Aerobic rice has higher N fertiliser recovery rate than flooded rice, and hence there is scope for reduced N fertiliser requirement. Water saving due to the use of quick maturing varieties was quite high and when these varieties were able to maintain a yield level similar to that of late maturing varieties, an increased WUE resulted. This review concludes with possible challenges and approaches that may be taken to increase WUE. Development of screening methods and identification of traits adapted to aerobic soil condition is required for the development of varieties to improve WUE of aerobic rice.