Growth, yield performance and nitrogen use efficiency of wheat as affected by nitrogen fertilization under arid agro-climatic conditions

Overuse of nitrogenous fertilizers and low productivity of cropping systems produce the lowest nitrogen use efficiencies (NUE) in Pakistan. The surplus nitrogen (N) causes environmental degradation and reduces farm profitability. There is a lack of consideration of NUE while setting yield targets and nitrogen fertilization rates. The NUE is an essential indicator for sustainable crop production. The NUE can be improved with optimum nitrogen application without compromising crop yields. To find out an optimum nitrogen level for high NUE in wheat under agro-climatic conditions of Multan, an RCBD experiment comprising six nitrogen fertilizer doses (0, 50, 100, 150, 200, and 250 kg ha-1) was conducted during 2017-18 and 2018-19. Increasing levels of N increased the growth and yield attributes, while the maximum cost-benefit ratio was recorded at 150 kg N ha-1. Higher N doses (200 and 250 kg N ha-1) increased the biological yield but did not translate into grain yield, reducing the harvest index and cost-benefit ratio. Several N use efficiency indices were established, showing that 100 kg N ha-1 recorded the maximum nitrogen use efficiency. Partial factor productivity, internal efficiency, and physiological efficiency were maximum at a lower dose (50 kg N ha-1). In contrast, agronomic efficiency, partial nitrogen balance, recovery efficiency, and NUE were maximum at 100 kg N ha-1. Higher N doses (150-250 kg N ha-1) reduced all the N use efficiency indices. It is concluded that with a yield objective of about 5 t ha-1 under the agro-climatic conditions of Multan, a nitrogen application of 100-150 kg N ha-1 will be the most economical and will produce the maximum nitrogen use efficiency for wheat.