Optimized Nitrogen Management For Wheat-rice Cropping System

Excessive and unreasonable application of nitrogen (N) result in low N use efficiency which is the main problem of rice-wheat rotation system in Yangtze River region. Determining the optimum N rate and N application methods for wheat and rice with the synchronization of soil N supply and crop N demand, could increase crop yields, improve nitrogen use efficiency and reduce nitrogen loss, which is of great importance to maintain the sustainable development of agriculture. The objectives of this paper were: (1) to determine the characters of N absorption and utilization during winter wheat and rice growing seasons, (2) to identify the suitable amount and timing of N application for rice and wheat, (3) to establish the SPAD(Soil and Plant Analynizer Development) threshold value across the critical growth stages in winter wheat and rice for N fertilization. Meanwhile, two treatments with basal N and without basal N application were conducted to determine whether the basal N fertilizer is necessary or not in winter wheat and rice under this experiment conditions. The outcome of current study was to provide scientific basis for optimizing nitrogen management of rice-wheat cropping systems in Yangtze River region. Main results obtained are summarized as follows:1.The results showed that the peak of N accumulation for winter wheat occurred from tillering to jointing stage and from booting to filling stage, and the corresponding N absorption accounted for 26.4% and 27.2% of total N uptake, respectively. While the peak of N accumulation for rice was from jointing to filling stage, and the N absorption of this period accounted for 31.3% of total N uptake. Therefore, it is significant to synchronize N supply with crop demand during the key growth periods in winter wheat and rice.2.It has been concluded that the optimizing N application for winter wheat and rice were 120-150 kg/hm~2 and 150 kg/hm~2 respectively. When the total amount of N fertilizer for wheat and rice was fixed, delaying N application properly and increasing the times of N splitting were beneficial to improve N efficiency. Taking the results of experiments and practical operation into account, the best N application method for winter wheat was that N fertilizer applicated with three times at basal, regreening and jointing stage, while the best N application method for rice was N fertilizer applicated with three times at basal, tillering and booting stage.3.Indigenous N supply (INS), is an important parameter of soil fertility during the entire growth periods. In general, no basal N fertilizer didn't significantly reduce wheat yield under a condition of high INS. In this experiment, no basal N fertilizer didn't significantly affect wheat yield when INS was more than 39 kg N/hm~2, indicating that soil N supply of this growing season was enough for the N requirement of winter wheat. While, no basal N fertilizer significantly reduced winter wheat yield when INS was less than 25 kg N/hm~2.4.It was significant to increase crop yield and N use efficiency by guiding N topdressing based on SPAD threshold value. The SPAD values vary with crop cultivars. In current study, the suitable SPAD threshold value for guiding N topdressing during the critical growing stages of winter wheat was 46 for RTNM(Real-time nitrogen management) and 46-48 for SSNM(Site-specific nitrogen management), respectively. While suitable SPAD threshold value for rice YLY 6 and PLY 3076 were 41 for RTNM and 39-41 for SSNM, respectively.