Abstract: Taking the single cropping of rice in rice-wheat double cropping system in the Huaibei region of Jiangsu Province as the object, this paper studied the effects of different nitrogen appli-cation rates on the yield and matter production of super rice under different levels of soil fertility. Super rice Xudao 3, a representative middle-season and middle japonica rice variety in the region, was selected as the test material , and the soils selected had fertility levels of high, medium, and low.  The grain yield, yield components, and population traits of Xudao 3 were investigated. There were extremely significant conic relationships between nitrogen application rate and grain yield under three soil fertility levels (r_high=0.959**,r_middle=0.971**,r_low=0.981**).  The grain yield was the highest under high level of soil fertility, followed by under medium, and under low level soil fertility. Under different soil fertility levels, the rice population in the treat-ment achieved the highest yield showed better traits, including appropriate leaf area index, rea-sonable tiller dynamics, higher population spikelets, and post-anthesis dry matter accumulation, at different growth stages. The optimal nitrogen application rate achieving the maximum yield un-der the high, medium, and low soil fertility levels was 260.3, 290.7, and 345.8 kg·hm^-2, re-spectively, which could be used as the recommendation for the optimum nitrogen application rates in Huaibei region of Jiangsu. Through the demonstration experiments in the region, high grain yield and N-saving effect were obtained.

Key words: Rare earth, Rape sclerotiniose, Disease index