| This research was aimed to find out the propositions for rapeseed production, by combining with field experiments and lab testing, including the effect of nitrogen(N), phosphorus(P) and potassium(K) fertilizer application rate on rapeseed yield, quality, profit, fertilizer use efficiency and farmland nutrient balance, the correlation between soil nutrient content and fertilizer application rate have been investigated and the technology of optimum fertilizer application of rapeseed for different soil available nutrient content have also been established in the research. The main results were shown as following:1. The results showed that rapeseed yield increased significantly when N, P and K were supplied adequately. (1) Compared with the treatment without N fertilization, N fertilizer application increased the average yield of rapeseed by 1218 kg/hm2 for 48 trails. The percentages of increased yield between 500 and 1000 kg/hm2, between 1000 and 1500 kg/hm2, and more than 2000 kg/hm2 were as high as 29.2%, 31.3% and 12.5% for all trails, respectively. The average increment rate was 122.0%, the increment rate between 80% and 120%, and over 120%, account for 22.9% and 35.4%, respectively. (2) Compared with the treatment without P fertilization, P fertilizer application increased the average yield of rapeseed by 626 kg/hm2 for 47 trails. The percentages of increased yield between 300 and 600 kg/hm2, between 600 and 1000 kg/hm2 and more than 1000 kg/hm2 trails account for 35.4%, 33.3% and 12.5%, respectively. The average increment rate was 45.3%. The increment rate between 10% and 30%, and more than 100% trails were as high as 47.9% and 10.4%, respectively. (3) Compared with the treatment without K fertilization, K fertilizer application increased the average yield of rapeseed by 361 kg/hm2 for 47 trails. The increased yield between 0 and 200 kg/hm2, between 200 and 500 kg/hm2, and over 800 kg/hm2 trails account for 33.3%, 39.6%, and 8.3%, respectively. The average increment rate was 20.0%, The increment rate between 5% and 10% and over 30% trails account for 29.2% and 20.8%, respectively. (4) Compared with no fertilization, the average increment yield of recommended fertilization was 1414 kg/hm2 and average increment rate was 164.1% for 61 trails. Compared with conventional fertilization, the average increment yield of recommended fertilization was 310 kg/hm2 and average increment rate was 16.3% for 24 trails.2. The results revealed that the profit of rapeseed increased significantly when N, P and K fertilizers were applied adequately. (1) Compared with PK treatment, the average net profit of NPK treatment was up to 5100 Yuan/hm and the value cost ratio (VCR) was 6.90 for 48 experiments, according to the fertilizer and rapeseed prices in 2007 and 2008. The net profit between 2000 and 4000 Yuan/hm2, between 4000 and 6000 Yuan/hm2 and over 6000 Yuan/hm2 experiments occupy 29.2%, 25.0% and 31.3%, respectively. The value cost ratio between 4.0 and 6.0, between 6.0 and 8.0, and more than 8.0, occupy 22.9%, 22.9% and 37.5%, respectively. (2) Compared with NK treatment, the average net profit of NPK treatment was up to 2661 Yuan/hm2 and the value cost ratio (VCR) was 7.71 for 47 experiments. The net profit between 1500 and 3000 Yuan/hm2, and more than 3000 kg/hm2,occupy 37.5% and 35.4%. The value cost ratio between 2.0 and 5.0, between 5.0 and 8.0, and over 8.0, account for 25.0%, 25.0%, and 43.8%, respectively. (3) Compared with NP treatment, the average net profit of NPK treatment was up to 1437 Yuan/hm2 and the value cost ratio (VCR) was 4.42 for 45 experiments. The net profit ranged from 500 to 1000 Yuan/hm2 and ranged from 1000 to 2000 Yuan/hm2 both account for 22.9% and exceed 2000 kg/hm2 experiments occupy 25.0%. The value cost ratio ranged from 2.0 to 5.0 and ranged from 5.0 to 8.0 account for 39.6% and 29.2%, exceed 8.0 occupy 8.3%. (4) Compared with no fertilization, the average net profit of recommended fertilization was 5392 Yuan/hm2 for 61 experiments. Compared with conventional fertilization, the average net profit of recommended fertilization was 1253 Yuan/hm2 for 24 experiments.3. The results indicated that rational application of NPK fertilizer could improve the quality of rapeseed (1) With the increasing of N fertilizer application rate, the content of protein and linolenic acid will increase , on the contrary, the content of erucic acid, stearic acid, oil, olenic acid and linoleic acid of rapeseed will decrease. (2) With the increasing of P fertilizer application rate, the content of oil, oleic acide, linoleic, stearic acid and linolenic acid will increase. On the contrary, the content of protein will drop. (3) When K fertilizer application rate is less than 120 kg/hm2, the content of oil and oleic acid will increase, the content of sulfuric glucoside, erucic acid and stearic acid will decrease with adding K fertilizer application. However, the quality of rapeseed will drop when K fertilizer applied excessively.4. The results showed that nutrient uptake and accumulation were affected by the N, P and K fertilizers application. (1) With the increasing of N application rate, N absorbing ability of rapeseed will increase. In contrast, it will slightly decreased when increasing the rate of P and K fertilizers. (2) P absorption of rapeseed increased when adding P fertilizer, but it will decreased with the increment of the N fertilizer rate. (3) With the increasing of K fertilizer, K absorbing ability of rapeseed increased, as well as slightly decreased with increasing of N fertilizer rate. (4) The results of the experiments demonstrated that nutrient accumulation in rapeseed rised with appling NPK fertilizer. 5. The experimental results showed that the absorbed nutrient of N and P mainly distributed in seed, while K mainly distributed in silique and straw. Nutrient distribution in rapeseed was little influenced by the fertilizer application rate. On the test conditions, there are 68.5%～77.2% N, 73.7%～82.7% P and 10.3%～15.4% K allocation in seed, respectively.6. The results showed that rational application of N, P and K fertilizer could improve the fertilizer use efficiency. Under test condition, the average fertilizer agronomic efficiency and partial factor productivity of rapeseed were 4.48～9.00 kg/kg N, 3.91～10.36 kg/kg P2O5, 1.56～4.71 kg/kg K2O and 9.94～25.45 kg/kg N, 17.96～58.09 kg/kg P2O5, 13.24～39.08 kg/kg K2O, respectively. The average fertilizer apparent efficiency were 22.98%～36.05%, 13.41%～24.69% and 23.67%～72.77% of N, P and K for rapeseed, and the average fertilizer physiological efficiency were 13.97～22.49 kg/kg N, 22.51～54.28 kg/kg P2O5 and 1.12～9.40 kg/kg K2O, respectively. Fertilizer use efficiency are mainly effected by trail fertility of soil and amount of fertilizer.7. On the experimental conditions, the rapeseed need to absorb 3.22～4.79 kg N, 1.39～2.11 kg P2O5, 5.91～9.57 kg K2O and the ratio of N, P2O5 and K2O producting 100 kg rapeseed yield was 1 : 0.31～0.65:1.23～2.71. Nutrient requirement of rapeseed (biomass) was mainly influenced by rape varieties and fertilizer application rate.8. The research shown that farmland nutrient balance of rapeseed production in Hubei province expresses as N and P were surplus and K was deficit. When fertilizer application rate were 150, 180 kg N/hm2 and 75, 90 kg P2O5/hm2, the average surplus amount reached 48.2, 67.0 kg N/hm2 and 38.8, 35.7 kg P2O5 /hm2, respectively. At the same time, the average deficit K was up to 62.2 kg K2O/hm2 with 120 kg K2O /hm2 fertilizer was applied in rapeseed producing. Under conventional fertilization condition, the average surplus amount reached 101.1 kg N/hm2,30.6 kg P2O5 /hm2 and the average deficit K was 23.1 kg K2O/hm2, respectively.9. In this research, the average productivity rate of soil was 44.5% for 61 rapeseed production sites (its mean the average productivity rate of fertilizer can reach to 55.5%), and the soil productivity at 20%～40% and 40%～60% experiments occupied for 30.6 % and 46.8 %, respectively.10. The recommended rate of fertilization for rapeseed production could be definited under current productivity condition in Hubei province by combining with field experiment and fertilizer response equation.(1) The average optimum N application rate was 156.2 kg/hm2 for 48 tests. The percentages of N application rate ranged from 100 to150 kg/hm2 , ranged from 150 to 200 kg/hm2,and more than 200 kg/hm2 were as high as 33.3%, 39.6% and 31.3% for all trails, respectively. (2) The average optimum P2O5 application rate was 63.3 kg/hm2 for 47 tests. The percentages of P2O5 application rate ranged from 30 to 60 kg/hm2, ranged from 60 to 100 kg/hm2, and more than 100 kg/hm2 tests occupy 40.4%, 51.1% and 2.1%, respectively. (3) The average optimum K2O application rate was 83.2 kg/hm for 43 tests. The percentages of K2O application rate ranged from 50 to 80 kg/hm2, ranged from 80 to 120 kg/hm2, and more than 120 kg/hm2 tests occupy 46.5% , 5.6% and 11.6%, respectively.11. Through field trails and all study results, the regression equations between soil nutrients content and N, P and K fertilization recommended rate were established. The regression analysis showed that the optimum NPK recommended rates have significant negative correlation with the content of soil available N, P and K. And the fertilizer recommended rate of rapeseed in Hubei province could be obtained through the equations yN= 437.41-60.808Ln(xN) (rN=0.5501**, n=48), yP= 117.35-22.755Ln(xP) (rP=0.4768**, n=47), yK= 354.55-61.485Ln(xK) (rK=0.6034**, n=43) (y means N, P2O5 and K2O recommended rates and x means the content of soil available N, P and K). These regression equations could be used in soil testing and fertilizer recommendation for rapeseed producing in Hubei province.
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