Optimal nitrogen management to achieve high wheat grain yield, grain protein content, and water productivity: A meta-analysis

Nitrogen (N) addition is commonly employed to enhance wheat production, and the effectiveness is strongly influenced by site-specific factors encompassing environmental conditions and crop management practices. However, the current understanding fails to adequately account for the intricate and variable interactions among these factors. Consequently, we conducted a global meta-analysis to quantify the combined contributions of these factors to wheat yield, grain protein content (GPC), and water productivity (WP) and provide recommendations for optimizing N management. The results revealed a significant improvement in grain yield (14.85%), GPC (6.62%), and WP (10.79%) following the application of N. Moreover, higher N addition rates, the utilization of coated N fertilizer, post-anthesis fertilization, and multiple N applications exhibited enhanced outcomes in terms of yield, GPC, and WP in wheat systems. It was observed that applying 100-200 kg/ha of N was the optimal rate for maximizing yield, GPC, and WP. Medium soil texture and humid climate conditions showed a more pro-nounced increase in yield in response to N addition. Additionally, wheat yield demonstrated a stronger response to N addition benefits when the annual temperature was below 14 degrees C, while GPC showed a higher increase with temperatures exceeding 14 degrees C. Furthermore, adopting common N fertilization practices alongside irrigation and implementing pre-anthesis N addition in medium soil texture and humid climate conditions also contributed to achieving optimal wheat performance. The finding of this study serves as a guideline to support on-site N addition practice for wheat and to offer a reference to N management policy design across specific site conditions.