Nitrogen use efficiency in a wheat–corn cropping system from 15 years of manure and fertilizer applications

• Long-term field research proved that manure application with chemical fertilizer improved the nitrogen use efficiency (NUE) of wheat–corn rotation system the most especially in acid soil.
• Phosphorus is found to be another important factor to improve NUE up to 40–60% if soil is P deficient.
• Between the rotation crops, both grain yield and NUE of wheat were determined more responsive to P fertilization, and that for corn were more responsive to manure application.

Low nitrogen use efficiency (NUE) and adverse environmental impacts caused by N fertilization increasingly threaten the sustainability of agriculture. To develop strategies for efficient nutrient management, we investigated the effects of long-term (1991–2005) various fertilization regimes on yield, NUE and N agronomic efficiency (NAE) in a wheat–corn cropping system at four sites (Changping, Zhengzhou, Yangling, and Qiyang) in China. Treatments included unfertilized control (CK), chemical fertilization only (N, NP, NK, and NPK), manure application (supplying 70% N) with NPK (NPKm) and at 1.5× rate (1.5NPKm), and NPK with corn stover returned (NPKs). The NP and NPK treatments resulted in generally higher yield, NUE and NAE than the N and NK for both wheat and corn demonstrating the importance of P in NUE improvement. The manure treatments resulted in significant increase or no decrease in the overall system NUE in all four sites with the highest mean NUE (49%) from NPKm treatment. In acid soil at Qiyang, only manure treatments resulted in significant increases of NUE and NAE indicating the importance of organic amendment. Wheat was more responsive to P fertilizer and corn was more responsive to manure in NUE improvement. Thus an effective nutrient management strategy is to ensure adequate P supply for the wheat crop and manure application for the corn crop to improve overall NUE for the wheat–corn production system.