Interactive effects of irrigation frequency and nitrogen addition on growth and water use of Jatropha curcas

This study aimed to investigate the effect of nitrogen addition on growth and water use of pot-grown Jatropha curcas (J. curcas) under three irrigation frequencies, i.e. 4d (W1), 8d (W2) and 12d (W3). Results show that compared to W1, W3 significantly reduced net plant growth, leaf area, basal shoot xylem cross-section area, total dry mass and whole water storage capacity and total evapotranspiration under saving irrigation water of 21.0%, but increased irrigation water-use efficiency (WUEI) and crop water-use efficiency (WUEET) by 9.7 and 13.1%, respectively. Meanwhile, W3 had higher Huber value, which may improve transfer water efficiency from roots to shoots. Compared to no nitrogen treatment, nitrogen addition increased total dry mass, whole plant water storage capacity, total evapotranspiration, WUEI and WUEET by 13.4–38.1, 8.5–17.7, 14.9–17.5, 16.4–30.7 and 17.7–21.9%, respectively. Thus the optimal combination was the treatment with irrigation frequency of 12d and nitrogen supply, which can increase water-use efficiency.