Effects Of Nitrogen Rate And Ratio Of Nitrogen,Phosphorus,and Potassium On Dry Matter Accumulation And Grain Filling Of Castor Bean (Ricinus Communis L.)

As a promising oil crop and bioenergy crop,castor bean is receiving increasing popularity in the world.The imbalanced application of nitrogen,phosphorus,and potassium(NPK)is an important factor restricting the grain filling and the yield of castor bean.Appropriate ratio of NPK is of great significance for the growth and development,nutrient absorption and grain filling of castor plants.In this study,different nitrogen application rates and NPK ratios were set up to investigate their effects on grain yield and yield components,dry matter accumulation and nutrient accumulation of castor plants,and physiological characteristics and nutrient uptake of castor bean.This study is aimed to provide a sound application of nitrogen,phosphorus,and potassium for increasing the productivity of castor bean.phosphorusA field experiment,with Zibi 8 as the variety,was conducted on the Experimental Farm of Yangzhou University during two castor growing seasons of 2016 and 2017.There were two experimental factors,including nitrogen rate(225 kg hm-2 and 375 kg hm-2)and the ratio of nitrogen,phosphorus,and potassium(1:0:0,1:0.3:0.6,1:0.6:0.9and 1:0.9:1.2 of N:P2O5:K2O)in the experiment.The experiment was arranged in a two-factorial design with three replicates.The main results are the following.Increasing N rate and the NPK ratio significantly increased the number of panicles per plant,100-grain weight,grain number per panicle and grain yield.The effects of different N rates and NPK ratios on dry matter accumulation and distribution of castor bean were also significant.The increase in N rate significantly increased the dry weight of castor plants,decreased the leaf DW/stem DW and the weight percentage of pod in aboveground dry matter.From early budding stage of main spike(E)to the mature stage of main spike(M),the dry weight of castor bean was increased with the increase in NPK ratio,while at the mature stage of branch spike it increased first and then decreased with the increase in NPK ratio.The accumulation of nitrogen,phosphorus and potassium in aboveground parts of castor plant was significantly increased by increasing N rate and applying phosphorus and potassium appropriately.At vegetative growth stage,the increase in NPK ratio significantly increased the total accumulation of nitrogen,phosphorus and potassium in the aboveground parts of castor plant,while at reproductive growth stage,the total accumulation of nitrogen,phosphorus and potassium in the aboveground parts of castor plant increased first and then decreased with the increase in NPK ratio.The total accumulation of nitrogen,phosphorus and potassium in the aboveground parts of castor plant was significantly higher under the ratio of 1:0.6:0.9 than that under the other treatments.The main distribution destination of nitrogen,phosphorus and potassium at vegetative growth stage is leaf.After reproductive growth stage,the main distribution destination of nitrogen and phosphorus is panicle,while the main distribution destination of potassium is stem.Increasing N rate or applying phosphorus and potassium significantly increased the distribution proportion of nitrogen,phosphorus and potassium in leaves and stems,but it was not conducive to the distribution of nitrogen,phosphorus and potassium to panicle s.The increase in nitrogen application increased grain filling rate at mid grain-filling stage and the volume of 100 grains,volume growth rate and grain weight at late grain-filling stage,but had no significant effects on the 100-grain volume,volume growth rate and grain filling rate at early and mid-filling stages.In addition,the application of phosphorus and potassium also significantly increased the 100-grain volume,grain weight and grain-filling rate at early grain-filling stage,but had no significant effects on the volume growth rate.The effects produced by NPK ratio on 100-grain volume and grain weight were:1:0.9:1.2>1:0.3:0.6>1:0.6:0.9>1:0:0.6.The contents of nitrogen,phosphorus,potassium in pods and the contents of nitrogen and phosphorus in grains were positively correlated with N rate.Increasing nitrogen application also significantly increased potassium content in grain at mid grain-filling stage,but had no significant effects on potassium content in grain at early and late grain-filling stage.Compared with the ratio of 1:0.3:0.6,the nitrogen and phosphorus contents of pod and grain in the other ratios were significantly lower.The potassium content of pod was increased with the increase in NPK ratio,while the potassium content of grain was increased at early stage of grain-filling,and then increased and then decreased at middle and late stages of grain filling,among which,the grain potassium content is higher under 1:0.3:0.6 and 1:0.6:0.9 than other treatments.The soluble sugar content,sucrose content in pod and starch content at early grain-filling stage and mid grain-filling stage were negatively correlated with N rate,and the soluble sugar content and starch content in grains were also negatively correlated with N rate.However,the sucrose content in grains and starch content in pods at late grain-filling stage were positively correlated with N rate.The application of phosphorus and potassium significantly reduced the starch content in pods and grains.The ratio of 1:0:0 and 1:0.3:0.6 were more favorable for the synthesis of soluble sugar and sucrose in pods and starch formation,while the ratio of 1:0.6:0.9 was more favorable for the synthesis of soluble sugar and sucrose in grain.The activity of Sucrose phosphate synthase(SPS)enzyme and the Auxin(IAA)content was increased,while the content of Abscisic acid ABA and Zeatin nucleoside(ZR)content were decreased with the increase in N rate.The activity of SPS enzyme and the content of endogenous hormones in grains had no obvious responses to different NPK ratios.Among them,SPS content in grains was stable under the treatment of 1:0.3:0.6 as compared with other treatments.The ABA content in grains was significantly lower under 1:0:0 and 1:0.3:0.6 treatments than that under other treatments.The treatments of 1:0.3:0.6 and 1:0.6:0.9 were favorable for the synthesis of IAA in grains at early stage of grain filling,while the treatments of 1:0.6:0.9 and 1:0.9:1.2 were favorable for the synthesis of IAA in grains at mid and late grain-filling stages.The treatment of 1:0.6:0.9 and 1:0.9:1.2 were also favorable for the synthesis of ZR in grains at early and mid grain-filling stages,while the treatment of 1:0:0 and 1:0.3:0.6 were favorable for the synthesis of ZR in grains at the late filling stages.In the present study,the increase in N rate and the application of phosphorus and potassium fertilizers significantly promotes the growth,dry matter accumulation,nutrient accumulation and yield of castor.When the N rate was 375 kg ha-1,the NPK ratio was 1:0.9:1.2,castor plant growth,dry matter accumulation,accumulation of nitrogen and phosphorus in aboveground parts of plant and yield were most favorable and the highest yield reached 3001.62 kg ha-1.