Modifying nitrogen fertilization ratio to increase the yield and nitrogen uptake of super japonica rice

【Objectives】 Crop straw incorporation can increase soil organic matter and improve soil fertility, enhance crop yield and quality. However, it sometime inhibits rice growth in the vegetative stage due to accumulation of organic acids and N immobilization. Farmers usually deal with this phenomena through increasing the amount of nitrogen fertilizer in rice-wheat cropping system in the Yangtze Catchments. Excessive nitrogen input results in low nitrogen use efficiency and water and air pollution. Therefore, the optimization of nitrogen fertilization is important for the improvement of yield and nitrogen use efficiency of rice. 【Methods】 Local popular japonica rice cultivars, Wuyunjing 24 and Ningjing 3, were selected as material, field experiments were conducted in Xinghua County, Jiangsu Province, China in 2012 and 2013.Two nitrogen rates (N1: 300 kg/ha and N2: 345 kg/ha) and two nitrogen application methods conventional fertilizer-nitrogen practice (CFP, basal:tillering:earring =3:3:4) and modified fertilizer-nitrogen practice (MFP, basal:tillering:earring =4:3:3) were designed. The yield, yield components, dry matter accumulation, nitrogen uptake and nitrogen use efficiency were investigated. 【Results】With the increase of the nitrogen fertilizer rate, the unit area panicles of rice are increased significantly, but the spikelet per panicle, filled-grain percentage and 1000-grain weight are decreased, finally, the grain yield increase is not significant. The grain yield is higher using MFP than CFP, owing to the more panicles per unit area and the significant enhanced population spikelet as a result. The range of yield increase with the MFP in N1 is 5.18%-7.10%, higher than that in N2 (2.70%-4.29%). With the increase of nitrogen rate, the dry matter accumulation and nitrogen uptake at the middle tiller stage and the jointing stage, from transplanting stage to the middle tiller stage, and from the middle tiller stage to the jointing stage are significantly improved, but the dry matter accumulation and nitrogen uptake increases at the maturity are not significant, the nitrogen agronomic efficiency, nitrogen recovery efficiency and nitrogen partial factor productivity are consequently decreased significantly. In comparison with CFP, the dry matter accumulation and nitrogen uptake amount and rate from the transplanting stage to the middle tiller stage are improved significantly under MFP. The dry matter accumulation and nitrogen uptake at the maturity and nitrogen agronomic efficiency, nitrogen recovery efficiency, nitrogen physiological efficiency and nitrogen partial factor productivity of MFP are higher than those of CFP and the differences of those are significant in N1, and the dry matter accumulation and nitrogen uptake at the maturity, nitrogen agronomic efficiency, nitrogen recovery efficiency, nitrogen physiological efficiency and nitrogen partial factor productivity are increased by 6.52%, 5.55%, 13.36%, 8.55%, 4.44% and 5.29%, respectively. 【Conclusions】Under the straw completely incorporation, increasing the nitrogen fertilizer rate will not increase the rice yield, but decrease the N use efficiency. Keeping the normal nitrogen fertilizer input, modifying the ratio of nitrogen fertilizer input of basal:tillering:earring from 3:3:4 to 4:3:3 will be capable of significant increase of yield, dry matter accumulation, N uptake and N use efficiency in mechanical transplanted super japonica rice with wheat straw return.