3.3. Water and nitrogen use efficiency
The data on water use efficiency as estimated from total tuber yield per seasonal crop ET varied widely under different irrigation and N levels (Table 3). The water was used more efficiently in the deficit irrigation treatments where lower amounts of water generally have higher WUE values. The highest WUE value, 195 kg ha−1 mm−1, was obtained at W0.4 with N220 level while the lowest value, 90 kg ha−1 mm−1, was obtained at W1.0 with N160. As the amount of water applied was lower by 20% (W0.8), WUE was 16.7% higher than at W1.0 with N340, although the increase in tuber yield was only 7.4%. In general, improved WUE can be achieved either by achieving same yield with reduced water or by deficit irrigation strategy and irrigation scheduling through reduction of water losses by evaporation.