Responses of Seed Yield and Economic Benefit of Winter Oilseed Rape（Brassica napus L.）to Different NPK Ratio and Dose

Yingzi WANG，Chang TlAN，Xuan ZHOU，Wenming WANG，Jianwei PENG*，Zhenhua ZHANG，4，Haixing SONG，4*，Chunyun GUAN

1.College of Resources and Environment，Hunan Agricultural University，Hunan Provincial Key Laboratory of Farmland Pollution Control and Agricultural Resources Use&Hunan Provincial Key Laboratory of Plant Nutrition in Common University&National Engineering Laboratory of College of Resources and Environment，Changsha 410128，China；

2.College of Horticulture and Landscape，Hunan Agricultural University，Changsha 410128，China；

3.College of Environmental Science and Resources，Zhejiang University，Hangzhou 310058，China；

4.Southern Regional Collaborative Innovation Center for Grain and Oil Crops in China，Changsha 410128，China；

5.Hunan Branch，National Center of Oilseed Crops Improvement，Changsha 410128，China

Responses of Seed Yield and Economic Benefit of Winter Oilseed Rape（Brassica napus L.）to Different NPK Ratio and Dose

Yingzi WANG1，2，Chang TlAN1*，Xuan ZHOU3*，Wenming WANG1，Jianwei PENG1**，Zhenhua ZHANG1，4，Haixing SONG1，4*，Chunyun GUAN5

1.College of Resources and Environment，Hunan Agricultural University，Hunan Provincial Key Laboratory of Farmland Pollution Control and Agricultural Resources Use&Hunan Provincial Key Laboratory of Plant Nutrition in Common University&National Engineering Laboratory of College of Resources and Environment，Changsha 410128，China；

2.College of Horticulture and Landscape，Hunan Agricultural University，Changsha 410128，China；

3.College of Environmental Science and Resources，Zhejiang University，Hangzhou 310058，China；

4.Southern Regional Collaborative Innovation Center for Grain and Oil Crops in China，Changsha 410128，China；

5.Hunan Branch，National Center of Oilseed Crops Improvement，Changsha 410128，China

Field experiments were conducted during 2008-2010 to investigate the effects of NPK fertilization on seed yield and economic benefit of a new hybrid cultivar of winter oilseed rape （Brassica napus L.）-Xiangzayou763，and to determine the optimum NPK ratio and dose in Hunan，China.The results showed that NPK ratio （1∶0.50∶0.50）with 180 kg/hm2N，90 kg/hm2P2O5and 90 kg/hm2K2O was the optimum combination for the highest seed yield （2 231.13 kg/hm2）and economic benefit （9 816.97 Yuan/hm2），of which 1 641.23 Yuan/hm2being set for fertilizer investment （VCR=4.11）.Besides，the effects of N，P and K fertilizers on seed yield and oil production of winter oilseed rape were not identical.N had the greatest effect on plant growth of winter oilseed rape，followed by P and K.Total leaf number，green leaf number，leaf length and width，rhizome diameter，branch number，dry weight per plant and other agronomic characters in high Ntreatments were higher than those in low N treatments.By correlation and path analysis of yield components，the contribution rate to seed yield was found:effective silique number per plant＞seed number per silique＞1 000-seed weight.

NPK ratio and dose；Seed yield；Economic benefit；Winter oilseed rape

O ilseed rape （Brassica napus L.）is a major oil crop and feed crop in China，and a promising biodiesel crop as well［1］.Rape production among small holder farmers is important for its nutritional and income generation［2-3］.As the largest economic crop in Hunan Province of China，oilseed rape is grown at least 10 000 km2per year［4］.In recent years，with the development of technique of fertilization and breeding for oilseed rape，more attention has been paid to the breeding of new varieties of oilseed rape and its fertilization［5］.However， oilseed rape which is grown at high density needs high inputs to ensure its production and quality.

Nutrient management in soil on sustainable basis includes fertilizer types，amounts，time and methods of their application.Proper amount and time of fertilizer application is considered a key to the bumper crop［6］.Wang et al.［7］found that，compared with no fertilizer，the scientific fertilization of NPK increased the seed yield of rape by 173.7%，much more than that of rice（46.7%），wheat（109.8%）and cotton（68.6%）.And the results of 386 field experiments indicated that the reasonable combination of N，P and K significantly increased crop yield［8］. Thus，it is necessary to optimize the allocation of fertilizers for maximizing the yield of oilseed rape.Some researches had been done by Central China Agricultural University for oilseed rape growth in Hubei and Yangtze drainage area ofChina，which have recommended reasonable NPK ratio and dose［9-13］.Results above have provided supports for scientific fertilization and technological generalization in oilseed rape production［1，14］. However，the reasonable applications of N，P and K have not been completely determined especially under different fields and production conditions.Therefore，the objective of this study is to determine the effect of different combinations of NPK on the seed yield of winter oilseed rape and recommend the optimal ratio and dose of NPK in Hunan of China，and provide theory basis for cultural technique system of a new good-quality and high-yield variety.

Materials and Methods

Site description

The experimental site is situated at the experimental station of Yong'an Town，Liuyang City，Hunan Province，Central China.This region has a typical continental sub-tropical humid monsoon climate with an annual mean temperature of 17.3℃and an annual average rainfall of 1 171.6 mm.Thesoil，classified as a reddish yellow soil，evolved from the red earth platform of quaternary period.The main soil properties （0-20 cm depth）of this study site are described in Table 1.

Materials

Winter oilseed rape variety tested-Xiangzayou763，provided by the China National Grain and Oils Improvement Center of Hunan，was cropped after double-cropping rice（forecrop）.Fertilizers were applied as urea （N 46%），calcium magnesium phosphate（P2O512%），potassium chloride （K2O 60%）and borax（B 11.3%）.

Experimental design

Test Ⅰ:Keeping in view of the conventional fertilization amount，treatments with different NPK fertilizer combination were selected.The doses of N and P2O5were set for two levels-180，150 kg/hm2and 90，60 kg/hm2. The dose of K2O was set for three levels-210，158 and 105 kg/hm2.There were 12 different ratios of NPK treatments（Table 2）.

Test Ⅱ:To further confirm the reliability of Test Ⅰ，field trials with relatively higher content of available K were performed at the neighboring village. The amount of K2O was reduced to 90，120 and 150 kg/hm2，adding another level of N （210 kg/hm2）and P2O5（120 kg/hm2）（Table 3）.

Winter oilseed rape was transplanted in October 2008/2009 and harvested in May 2009/2010.In detail，25 day-old seedlings were transplanted to plots of 20 m2（4 m×5 m）each，separated with ditches of 20-25 cm deep，giving a population of 30 hills/m2.

The treatments along with fertilizers applied are described in Table 2 and Table 3.Treatments were arranged according to completely randomized block design with three replications.50%N，60%K2O，100%P2O5and 100%B were applied as basal fertilizers by scattering at one time，20%N and 20%K2O as seedling fertilizer，30%N and 20%K2O as bolting fertilizer. Tillage，mechanical and chemical control of agricultural pests in the plantation were typical for this plant specie and consistent with the recommendations for protection.

Sampling and analysis

Plant samples were collected at maturity stage，and branch number， effective silique number，seed number，branch height and plant height were recorded.Seeds of each plot were harvested，oven-dried for 4 d at 60℃，and weighed to obtain seed yield.Oil content（%）was determined by taking 100 g cleaned seeds from each treatment，which were crushed and oil was extracted by soxlet method［15］.

Statistical analysis

All the statistical analyses were performed by using the SPSS 17.0 package （SPSS，Chicago，IL，USA）. Statistically significant differences were identified using analysis of variance （ANOVA）；Duncan's Multiple Range Test was conducted to determine significant mean differences at 0.05 probability.

Oil yield=Seed yield×Oil content；

Seed output=Seed yield×Seed price；

Fertilizer investment=N amount× N price+P2O5amount×P2O5price+ K2O amount×K2O price+B amount×B price.

Seed and fertilizer price were seasonal prices.

Table 1 Selected physico-chemical properties of the soil

Table 2 Experimental treatments showing all possible combination of NPK for TestⅠkg/hm2

Results and Analysis

Seed yield

The seed yield of winter oilseed rape showed significant response to the various combinations of NPK fertilization （P＜0.05；Fig.1 and Fig.2）.A-mong the treatments in Test Ⅰ，Treatment 1 had the highest seed yield（1 829.99 kg/hm2），followed by Treatment 2（1 800.47 kg/hm2）.Compared with CK，Treatment 1 and Treatment 2 increased the seed yield by 1 394.57 and 1 365.05 kg/hm2，respectively.Under the same dose of P and K，the seed yield in high N treatments（Treatment 1-Treatment 6）were higher than those in low N treatments（Treatment 7-Treatment 12），above 1 680kg/hm2（P＜0.05）.Besides，P displayed the similar trend，namely the seed yield in high P treatments（Treatment 1-Treatment 3 and Treatment 7-Treatment 9）were also higher than those in low P treatments（Treatment 4-Treatment 6 and Treatment 7-Treatment 9），while K did not.

Table 3 Experimental treatments showing all possible combination of NPK for Test Ⅱ kg/hm2

In Test Ⅱ，Treatment B had the highest seed yield （2 231.13 kg/hm2），which was obviously higher than other treatments（P＜0.05），followed by Treatment G（2 065.26 kg/hm2），which was obviously higher than Treatment D，Treatment F and CK（P＜0.05）.And the lowest seed yield of NPK treatments was in Treatment F，1 608.23 kg/hm2.Under the same dose of P and K，the seed yield increased along with N（e.g.Treatment A，Treatment F and Treatment G），while P was consistently（e.g.Treatment A，Treatment D and Treatment E）.The seed yield did not increase by applying more K，and even decreased instead （e.g.Treatment A，Treatment B and Treatment C）.Results indicated that the responses of winter oilseed rape in seed yield followed the order of N＞P＞K.

In conclusion，under the same P and K level increasing N or under the same N and K level increasing P，both raised the seed yield of winter oilseed rape in two-year test.In Test Ⅰ and Ⅱ，Treatment 1（1:0.5:0.58），Treatment 2（1:0.5:0.88），Treatment5 （1:0.33: 0.88），Treatment B （1:0.50:0.50）and Treatment G （1:0.43:0.57）were the optimum treatments in the seed yield. Although the volume variances for these treatments were not significant（P＞0.05），the best NPK combination of two-year experiment was obtained as 1:0.50:0.50，with 180 kg/hm2N，90 kg/hm2P2O5，90 kg/hm2K2O based on the reduction of K application.

Correlation and path analysis of yield and its components

Taking effective siliques number per plant（X1），seed number per silique（X2）and 1 000-seed weight（X3）as the independent variables，and seed yield（Y）as dependent variable，correlation analysis and path analysis of two-year experiment，multivariate regression analysis were performed to establish a regression equation of three components on seed yield as below.

Y=-3 425.56+45.66X1+33.14X2+ 236.22X3（F=78.22**，R=0.9814）TestI；

Y'= -2 580.94+8.56X1'+ 109.50X2'+359.55X3'（F=20.98**，R= 0.969 7）Test Ⅱ.

Correlation analysis and path analysis of two-year experiment（Fig. 3:Test Ⅰ，Fig.4:Test Ⅱ）on the three yield components and seed yield were performed.In the two-year experiment，the coefficient of efficient siliques number per plant was the highest in either path coefficient or correlation coefficient（P＜0.01），indicated that a certain number of effective siliques per plant was the foundation of winter oilseed rape for high yield.Besides，the path coefficient of 1 000-seed weight was higher than that of seed number per silique，while the correlation coefficients in TestⅠdisplayed negative value（-0.279），which needs further study to confirm.

The three yield components effective silique number per plant，seed number per silique and 1 000-seed weight existed significant interaction mutually（P＜0.05）.It indicated that the seed numbers per silique could had an indirect effect on the seed yield by silique number per plant.

Consequently，it was suitable to increase the seed yield by improvement of silique number per plant.This fact indirectly emphasized the importance of the period from the stage of eargrowth to the stage of seed growth，which was decisive for final formation of the seed yield.Of yield components，it was further confirmed that effective silique number per plant had the greatest effect on seed yield，followed by 1 000-seed weight and seed number per silique.

Oil yield

In Test Ⅰ，the maximum oil yield of winter oilseed rape at harvest（Fig.5）was achieved by Treatment 2（7 37.61 kg/hm2），followed by Treatment 1（737.21 kg/hm2）.In Test Ⅱ，the maximum oil yield of winter oilseed rape at harvest （Fig.2）was achieved by Treatment B（938.25 kg/hm2），followed by Treatment G（737.21 kg/hm2）.Therewere no significant differences among these treatments in oil content（40.40%-41.70%）like seed yield（P＞0.05）.And high N treatments（40.40%-40.90%）were lower in oil content than those of low N treatments （41.13%-41.70%）.Namely high N treatments had higher seed yield，but relatively lower oil content.As shown in Test Ⅱ（Fig.6），Treatment B had the highest oil yield （938.25 kg/hm2），followed by Treatment G （869.96 kg/hm2）.Within the range of oil content （41.93%-42.96%），oil yield had the similar trend with seed yield.

In conclusion，the trend of oil production in general depended on seed yield.For oil content differed slightly among these treatments，and there was a decrease in oil content with N ratio increasing.Zhao et al.［16］found a similar result，namely with the increase of N application rate，oil content very significantly decreased，oil content would be reduced by 0.21%-0.24% with N increasing by every 1 kg.Thus，oil yield and seed yield had the same trend，and the differences of oil yield in each treatment were not so obvious as seed yield.

Table 4 Economic benefits of winter oilseed rape（Test Ⅰ） Yuan/hm2

Economic benefit

The statistical analysis showed that economic benefit was significantly affected by different NPK treatments（P＜0.05；Table 4 and Table 5）.In Test Ⅰ，the seed output of winter oilseed rape in Treatment 1 was the highest（7 319.96 Yuan/hm2）（Table 4）.After deducting the fertilizer investment，of which fertilizer efficiency also achieved maximum，3 905.26 Yuan/hm2（VCR= 2.33），followed by Treatment 4（VCR= 2.25）.According to the actual situation of China's agricultural production，the fertilizer application in VCR＞2.0 had remarkable economic benefits［14］.On the other hand，the higher economic benefit was obtained in the treatments with lower K application，indicated that K had a certain influence on the VCR. By analyzing the economic benefit，we found that Treatment 1 （1∶0.5∶0.58）was the most suitable ratio of NPK. In Test Ⅱ，the seed output in Treatment B was9816.97Yuan/hm2（Table 5）with the lowest fertilizer investment 1 641.23 Yuan（VCR=4.11），followed by Treatment A，of which fertilizer efficiency amounted to 5 572.78 Yuan/hm2，and VCR surpassed 2.0（P＜0.05）.As a consequence of economic benefit，Treatment B achieved the highest seed output and VCR for the lowest fertilizer investment.

Table 5 Economic benefits of winter oilseed rape（Test Ⅱ） Yuan/hm2

Discussion

Nitrogen is considered as major element of fertilizer for high yield and closely linked to the control of vegetative growth of plant and hence determines the fate of reproductive cycle. Phosphorous is required in a smaller amount than nitrogen for plant growth and equally important for crop growth. Potassium is also required in a large amount by crop.NPK fertilization exerted a significantly higher and positive effect on yield oof maize and oilseed rape as compared with winter wheat and spring barley［17］.Higher yield per unit area can be achieved by adopting modern cultural practices with better nutrient management.Hence，the rapid growth of fertilizer input still has great potentiality for sustained agricultural production in China.Balanced application of N，P and K is considered as a guarantee of rational supply of essential nutrients for normal growth to sustain crop yield，increase fertilizer use efficiency and restore soil fertility under intensive cropping［18］.

Normally，it was needed to produce 100 kg oilseed with 10 kg N，3.6 kg P2O，11 kg K2O and 1.0 kg B in Hunan，China［19］.In Test Ⅰ，we found that Treatment 1 （1∶0.50∶0.58）with 180 kg/hm2N，90 kg/hm2P2O5and 105 kg/hm2K2O was the optimum ratio and dose for seed yield by reducing K application.On the other hand，it was further confirmed by Treatment B in Test Ⅱ.The researches in Jiangxi suggested that the application of K（90 kg/hm2）in a reasonable range could be recommended to properly reduce the whole application of NPK［20］.Due to the development of straw returning，K deficiency in soil for winter oilseed rape was largely alleviated in the Yangtze River area［21］.Moreover，to soil rich in K，applying more K would decrease the content of available Mg due to nutrient antagonism，resulting in a considerable reduction in production［22］.Most researches found N and P were the main nutrition elements affecting crop yield，followed by K［7，23-24］，while the influence of K application is minimal.Sun et al.［25］showed that with K application increasing，the seed yield conformed to parabolic model by the optimum amount of K at 135 kg/hm2in field，which was consistent with our results.Thus more studies are needed to determine K application combined with seed quality in the future.

Under the same ratio of P and K，high N treatments in total leaf number，green leaf number，leaf length and width，rhizome diameter，dry weight per plant and other agronomic characters were higher than those in low N treatments（Data not shown）.It indicated that the suitable ratio of NPK could improve the formation of agronomic characters to promote production［26］. Szczepaniak et al.［17］suggested that seed number per plant was a more sensitive component of yield structure response to balanced supply of basic nutrients than 1 000-seeds weight.In the test，the maximum correlation was between siliques number per plant and seed yield，followed by seed number per silique and1 000-seeds weight.

The oil production was calculated on the basis of the determined oil content and the seed production［27］.According to economic benefit of twoyear test，in Test Ⅰ，the fertilizer efficiencies of Treatment 1 （1∶0.5∶0.58）and Treatment 4 （1∶0.33∶0.58）were significantly obvious（P＜0.05），and the seed output and VCR of Treatment 1 were higher than those of other treatments.In Test Ⅱ，the seed output of Treatment A（1∶0.50∶0.67）and Treatment B（1∶0.50∶0.50）were significantly obvious（P＜0.05）.Due to higher K application，the fertilizer efficiency of Treatment A was lower than that of Treatment B by 1 168.56 Yuan/hm2. Analyzing the results of the two-year experiment，in Test Ⅱ Treatment B（1∶0.50:0.50）with 180 kg/hm2N，90 kg/hm2P2O5and 90 kg/hm2K2O was the most appropriate ratio and dose of NPK.

It could be conducted that Treatment 1 has the best NPK combination among the treatments for it produced similar seed yield but required lower K application compared with other treatments.Therefore，the combination of N，P，K and B fertilizers is a generally recommended technique in oilseed rape production in Hunan，China.Simultaneously，the economic profit from fertilizers would be reducing because the price of fertilizers has risen greatly in recent years［28］.In this regard，we suggest that one element nutrient will be tentatively reduced or even deducted from the total fertilizers if it is relatively abundant in soil.For instance，the application of K fertilizer can be lessened or ignored during some periods in the areas with high available K in soil. Moreover，the fertilization thresholds under different yield levels in various ecosystems and soil fertlity need further studies to conduct precise fertilization in the future.

Conclusion

（1）The NPK combination of Treatment B seemed to be the optimum dose and ratio in terms of maximum seed yield（2 231.13 kg/hm2）and oil yield（938.25 kg/hm2）in Hunan，and the methods of N application hadgreatest influence on seed yield and oil yield of winter oilseed rape，followed by P and K.

（2）Of yield components，the contribution rate to seed yield was further confirmed that:effective silique number per plant＞1 000-seed weight＞seed number per silique.

（3）The NPK ratio（1∶0.50∶0.50）of the tested treatments with 180 kg/hm2N，90 kg/hm2P2O5and 90 kg/hm2K2O in the seed output amounted to a maximum of 9 816.97 Yuan/hm2，with the lowest fertilizer investment（VCR= 4.11）.Considering all，it is the optimum combination for plant growth of winter oilseed rape.

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Responsible editor：Qingqing YlN

Responsible proofreader：Xiaoyan WU

Supported by the Youth Fund of Orient Science and Technology College，Hunan Agricultural University（14QNZ09）；Cultivation Physiology Station of National Technical System in Rape Industrial，National Key Technology Support Program（2012BAD15B04，2010BAD01B01）；Special Fund of Government in Hunan Province，National Natural Science Foundation of China（31071851，31101596，3132130）；Open Fund Project of Innovation Platform in Colleges and Universities of Hunan Province（12K064）.

*These authors contributed equally to this work.

**Corresponding author.E-mail:jwpngpd@sina.com，shx723@126.com Received:August 18，2015 Accepted:October 10，2015