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Interactive effects of sowing date and nitrogen fertilizer on water and nitrogen use efficiency in millet cultivars under drought stress

Abstract This study was conducted to investigate the effects of two irrigation regimes (55 and 85% of soil available water depletion) and two nitrogen levels (0 and 112.5 kg ha−1) on yield as well as water and nitrogen use efficiencies of two millet cultivars (namely, Bastan and Pishahang) planted at two sowing dates during 2015 and 2016. Growth parameters and nitrogen use of the millet cultivars were found affected by drought, nitrogen level, and sowing date as well as their interactions. Nitrogen application was found to improve not only nitrogen uptake, chlorophyll content, and irrigation water use efficiency (IWUE) but also grain and biological yields; more positive effects were, however, observed under the control irrigation regime. Nevertheless, nitrogen uptake (NUpE), utilization (NUtE), and use (NUE) efficiencies decreased as a result of nitrogen application. The increases in grain yield (16 versus 7%) and IWUEg (17 versus 6%) due to nitrogen application were more pronounced in the drought-tolerant Bastan cultivar than in the drought-sensitive Pishahang. However, nitrogen application decreased NUpE in both cultivars. Although water stress increased soil N residual with all the sowing dates, the increase was greater with the early ones. The results of the experiment suggest that the application of higher nitrogen levels is not the proper strategy for compensating for the reduced yield under drought conditions. Rather, late sowing dates, due to the lower drought effects associated, might be the proper alternative for achieving higher yields as well as improved IWUE and NUE in areas plagued with water shortage.