| Rapeseed-rice rotation is one of the most representative and extensive farming system in the middle and lower reaches of the Yangtze River. With the change of cultivation system, the improvement of yield potential and the regeneration of crop variety inrecent years. Plant's dependence on the fertilizer is enhanced and requirements on nutrient management are constantly improving. This research studied the effect of N, P, K fertilizer application on yield, nutrient absorption and accumulation, quality, nutrient balance, soil nutrient transformation, fertilizer efficiency, economic profit and recommended fertilization quantity in rapeseed-rice rotation in Hubei Province. The main results were as follows:1. Yields of rapeseed and rice were increased significantly by the application of N, P and K, which obtained good effect on yield in rapeseed-rice rotation system. In rape growth reason, when applied 90～360N kg/hm2,45～180 P2O5kg/hm2 and 60～240 K2O kg/hm2, rapeseed yield could be increased for 576-1219kg/hm2,100～328kg/hm2,205～433kg/hm2. Rape yield reached the highest at 180kg N/hm2,90kg P2O5/hm2,120kg K2O/hm2, Increased yield by 1155 kg/hm2,328 kg/hm2,433 kg/hm2 respectively. In rice growth reason, when applied 90～360N kg/hm2,22.5～90 P2O5 kg/hm2 and 30～120 K2O kg/hm2, they could increase yield by 1490-3224kg/hm2,1084～1184kg/hm2,211-728kg/hm2, rice yield gained the best effect at180kg N/hm2,45kg P2O5/hm2,60kg K2O/hm2, Increased yield by 2646kg/hm2,1184kg/hm2,728kg/hm2 respectively.2. The nutrient's uptake and accumulation of rape and rice's could be promoted by N, P and K application. Added one fertilizer rate can raise this nutrient's accumulation, but excessiveness inhibited other nutrients' accumulation. As nutrient distribution on maturity, most of N and P accumulated in rapeseed, and most of K accumulated in stalk and legume for rape. Majority of N and P in grain and majority of K in stalk for rice.3. The quality of rapeseed and rice were be influenced by fertilization significantly. For rapeseed, nitrogen increased oleic acid and protein content, reduced erucic acid content. Phosphorus increased glucosinolate content. Potassium increased oil content of rapeseed. For rice, nitrogen raised milled rice rate and protein content, reduced amylase content. Phosphorus raised milled rice rate and alkali spreading value. Potassium raised milled rice rate, protein content and alkali spreading value.4. In rapeseed-rice rotation system, yields got the highest at 2654kg rapeseed/hm2, 9544kg grain/hm2 when fertilizer application of 360kg N/hm2 (rapeseed 180kg/hm2-rice 180kg/hm2),135 kg P2O5/hm2 (90-45kg/hm2),180kg K2O/hm2 (120-60kg/hm2). The surplus 143.0 kg N/hm2 and 100.6 P2O5/hm2 was being,163.1 K2O/hm2 was deficit during this time.In rape growth reason, N, K got the highest accumulation at returning green stage, and P at bolting date. In rice growth reason, it is the highest for N, K accumulation during heading date. Time for the highest accumulation of P gone back, which during the period between heading date and maturity.5. Fertilization increased the fertilizer efficiency on rapeseed and rice significantly. In rapeseed-rice rotation system, it got the highest fertilizer efficiency by the fertilizer application of 360kg N/hm2(rapeseed 180kg/hm2～rice 180kg/hm2),135 kg P2O5/hm2(90～45kg/hm2),180kg K2O/hm2(120～60kg/hm2), that the fertilizer efficiencies were 35.30%, 16.88% and 36.38 respectively.6. The application of N, P and K on rice and rapeseed all obtained high profit. In rapeseed-rice rotation system, the largest net economic profit were get at the fertilizer application of 360kg N/hm2(rapeseed 180kg/hm2～rice 180kg/hm2),135kg P2O5/hm2 (90～45kg/hm2),180kg K2O/hm2(120～60kg/hm2), which increased income 7937yuan, 2808yuan and 1571 yuan per hectare respectively than corresponding deficiency treatments.7. Through this study, we got optimum fertilization for the region as follows:In rape growth reason,233～285kg N/hm2,83～101kg P2O5/hm2,106～130kg K2O/hm2. In rice growth reason,242～314kg N/hm2,40～62kg P2O5/hm2,45～67kg K2O/hm2.
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