Photosynthetic Response of Maize to Nitrogen Fertilization in the Semiarid Western Loess Plateau of China

Agriculture in rainfed dry areas is often challenged by inadequate water and nutrient supplies. Responses to these challenges include adequate fertilization, but it is unknown whether different nitrogen (N) rates from that commonly used in the Loess Plateau can alleviate this issue. Field experiments were conducted over three cropping seasons to investigate the effect of different N fertilization levels on soil water dynamics, photosynthetic activity, and grain yield of maize ( Zea mays L.) grown in the Western Loess Plateau of China. Fertilizer was applied at planting at rates between 0 and 300 kg N ha −1 at regular increments of 100 kg N ha −1 (referred to as N 0 and N 300 , respectively), and treatments were arranged in a complete randomized block design. Results showed that water use efficiency in the N 200 and N 300 treatments was ∼60% higher than N 0 and N 100 ( P < 0.05), which translated into increased crop biomass and therefore grain yield (≈70–80%). These observations were consistent with all measurements of photosynthetic traits and suggested that, under the conditions of this study, the ecophysiological response of the crop may be optimized at N application rates in the range of 200 to 300 kg ha −1 , depending on soil water availability. Agronomic efficiency calculations at this level of N fertilization reported consistently higher values and consequently suggested that environmental losses of applied fertilizer N were small. The current experimental results for the N application rates in the range of 200 to 300 kg ha −1 could be useful for improving N fertilizer and soil water management practices of maize production while maintaining a relatively stable yield level in rainfed dry areas. Future work should focus on optimizing timing and improving the placement of fertilizer N applied to maize.