Effects of nitrogen application methodologies on yield and nitrogen use efficiencies in a summer maize (Zea mays)-winter wheat (Triticum aestivum) rotation system

This research was conducted to explore an appropriate nitrogen (N) management pattern for a summer maize (Zea mays)-winter wheat (Triticum aestivum) rotation system (SM-WW) and to study the effects of N application methodologies on crop yields and N use efficiencies in a SM-WW in high and medium yield areas of Henan Province, North China. An appropriate N management strategy was analyzed and established in this study. The detailed N application strategies for the SM-WW were as follows:(i) no N application (T1); (ii) one-off application of urea with the rate of 210 kg(N)·hm^-2 (T2); (iii) fractional application of urea with the rate of 210 kg(N)·hm^-2 (T3); (iv) combined application of controlled-release N fertilizer with urea at the rate of 180 kg (N)·hm^-2 for wheat and 195 kg (N)·hm^-2 for maize (T4); (v) combined application of controlled-release N fertilizer with urea at the rate of 210 kg(N)·hm^-2 for wheat and maize (T5). The Soil-Plant Analyses Development (SPAD) chlorophyll meter (Minolta Camera Co., Japan) was used to determine SPAD values. Plant and/or grain N content and biomass were measured at different growth stages for the SM-WW and used to calculate different N indicators. Results showed that N fertilization methodologies could significantly affect the yield, yield components, and N indicators among the five treatments, with the overall trend being T5 > T4 > T3 > T2 > T1. Moreover, the yield and N parameters in high-yield area were significantly higher than those in medium-yield area. Compared with the medium-yield condition, the average values among the five treatments for yield, plant N content, and accumulation increased by 58.0%, 19.2%, and 47.1% for maize and 34.7%, 33.3%, and 85.9% for wheat, respectively, under high-yield conditions. Regarding the N use efficiencies, from T1 to T5, apparent N use efficiency, agronomic N use efficiency, and N absorption amount for producing 100 kg of grain were increased both in the high-and medium-yield areas. However, the opposite trend was found for N harvest index. The results showed that an optimal N fertilization treatment, such as T4 or T5, had great potential in improving N use efficiency without adversely affecting grain yield and could be an appropriate model of N nutrient application during the SM-WW in Henan Province, China.