Effects of nitrogen application rate and irrigation regime on growth, yield, and water-nitrogen use efficiency of drip-irrigated winter wheat in the North China Plain

Drip irrigation has been gradually adopted for winter wheat production in the North China Plain (NCP) due to significant saving from using irrigation water and improving water and nitrogen use efficiencies. However, the optimal water and nitrogen application rates for drip-irrigated wheat are still unclear. A field experiment with five nitrogen application rates (0, 120, 180, 240, and 300 kg ha(-1), referred as N0, N1, N2, N3, and N4) and three irrigation levels (40, 30, and 20 mm per irrigation, referred as I1, I2, and I3) was conducted during the 2015-2016 and 2016-2017 winter wheat seasons to study the effects of irrigation and nitrogen rates on crop growth, yield, and the water and nitrogen use efficiencies. Results showed that increasing irrigation and nitrogen application rates notably improved actual evapotranspiration, leaf area index, aboveground biomass, grain yield, and water use efficiency (WUE) of winter wheat. However, nitrogen application rates exceeding 240 kg ha(-1) were not beneficial for wheat growth, grain yield, WUE, and irrigation water use efficiency (IWUE). The maximum grain yields of 8034 and 8760 kg ha(-1) were achieved in N3I1, which had WUE of 2.08 and 2.23 kg m(-3), and IWUE of 4.46 and 4.87 kg m(-3) in 2015-2016 and 2016-2017, respectively. At the same time, N3I1 did not result in much reduction of nitrogen partial factor productivity (NPFP) (average of 34.99 kg kg(-1) in N3I1 for two seasons). Considering comprehensively growth, yield, WUE, IWUE, and NPFP, combination of N rate of 240 kg ha(-1) and irrigation quota of 40 mm per irrigation was optimal pattern for drip-irrigated winter wheat. These results may provide a scientific basis for water and nitrogen management of drip-irrigated winter wheat in the NCP.