Determining effects of water and nitrogen input on maize (Zea mays) yield, water- and nitrogen-use efficiency: A global synthesis

A major challenge in maize (Zea mays) production is to achieve high grain yield (yield hereafter) by improving resource use efficiency. Using a dataset synthesized from 83 peer-reviewed articles, this study mainly investigated the effects of water and/or nitrogen (N) input on maize yield, water productivity (WP), and N use efficiency (NUE); and evaluated the effects caused by planting density, environmental (temperature, soil texture), and managerial factors (water and/or N input). The input of water increased maize yield, WP, and NUE only when the input was less than 314, 709, and 311 mm, respectively; input of N increased maize yield, WP, and NUE until input was greater than 250, 128, and 196 kg ha(−1), respectively. Additionally, results of the mixed-effects model and random forest analysis suggested that mean annual temperature (MAT) was the most critical factor for narrowing gaps (between the actual and attainable variable, which was indicated as response ratio of the treatment relative to the control) of yield (RR(Y)), WP (RR(WP)), and NUE (RR(NUE)), respectively. Specifically, RR(Y), RR(WP), or RR(NUE) were negatively correlated to MAT when MAT was higher than 15 °C. Additionally, the structural equation model showed that water input and RR(WP) with the higher coefficient were more important than N input and RR(NUE) in improving RR(Y). These findings provide new insights into the causes and limitations of global maize production and offer some guidances for water and/or N managements.