Effect Of Insect-proof Net Cultivation On Rice Grain Yield And Quality Formation And Their Ecological And Physiological Mechanism

The diseases and insect pests are one of the most important factors that limit agricultural production.Chemical pesticide is the major control method of diseases and insect pests.Howerer,the excessive use of chemical pesticide increases the health risks for humans and pollutes environment.Therefore,developing the safe and effective methods to control rice diseases and insect pests is very important.Insect-proof net cultivation(EPN)is an environment friendly and effective control method of diseases and insect pests,which is also widely applied for seedling raising and seed production or breeding in rice.However,the effects of IPN on ecological and physiological mechanism of yield and quality formation in rice and the responses of rice grown in the insect-proof net to planting density and nitrogen application are still lack of systematic research.Therefore,cultivar experiment,planting density experiment and nitrogen application experiment were conducted for rice under the IPN.In order to identify the effects of IPN on yield and quality formation from physiological and ecological aspects,the effects of IPN on climatic factors,rhizosphere soil microbial and enzyme acitvity,and photosynthetic production,dry matter accumulation,distribution and translocation,as well as nutrient uptake and utilization of rice were analyzed.Then,the effects of planting density and nigtrogen application on rice yield formation under the IPN were determined.Our results will provide theoretical basis for designing planting density and nitrogen application measures and increasig rice yield and quality in the IPN.The main results were as follows:1.Efifects of IPN on ecological and physiological charactristics of yield and quality formation in rice.Compared with non-insect-proof net cultivation(NIPN),IPN significantly decreased rice yield by 23.52%-24.98%.IPN decreased light intensity in the net which reduced maximum tiller number and panicle rate,spikelet number per panicle and seed-setting rate.IPN shorten the effective accumulative temperature at grain filling stage and negatively affected photosynthetic production after heading,causing the decrease of 1000-grain weight.Generally,the decreased grain yield under the IPN manily caused by panicle number per unit area,followed by spikelet number per panicle,and seed-setting rate and 1000-grain weight had the smallest influence on grain yield.On the other hand,compared with NIPN,the lower light intensity in the IPN increased the leaf chlorophyll content,while decreased leaf area index and net photosynthesis rate,and reduced leaf area duration,net assimilation rate and crop growth rate of two rice cultivars,leading to a reduction in total biomass and harvest index.The lower total biomass and harvest index under the IPN caused the decrease of rice yield,and the decrease of total biomass had more negative effects on rice yield than harvest index.In addition,IPN decreased dry matter translocation(DMT),dry matter translocation effeciency of stem and leaf and the contribution of DMT to rice yield,which negatively affected the grain yield formation.IPN decreased the soil microbial,soil urease and acid phosphatase,as well as α-NA oxidizing amount of root and root dry weight,which had a negative effect on N,P,K absorption.Meanwhile,IPN significantly decreased the N,P,K translocation and translocation efficiency,and affected N,P,K accumulation after heading,therefore changed the contribution of N,P,K accumulation before heading on rice grain nutrient.Moreover,IPN decreased the N,P,K use efficiency for grain production,partial factor productivity of applied N,P,K,and N,P,K harvest index,while increased the N,P,K uptake for 100 kg grain.Compared with NIPN,IPN increased the air temperature and decreased the light intensity,which improved processing quality,appearance quality,nutritional quality,and cooking and eating quality to some extent.On the whole,better improvement of grain quality and lower yield loss were observed for Nanjing44 than Suxiangjing3 under the IPN.This indicated that Nanjing44 was more suitable for IPN than Suxiangjing3.2.Effects of planting density on grain yield formation in rice under the IPN.Under the IPN,with the increasing planting density,rice yield firstly increased and then decreased,and the highest rice yield was observed under 33.33‘104 hill·hm"2(D4)treatment.under the IPN,with the increase of planting density,panicle number per unit area gradually increased,and spikelet number per panicle gradually decreased.While planting density had little effects on seed-setting rate and 1000-grain weight under the IPN.This indicated that the variation of rice yield under different planting density treatments mainly caused by panicle number per unit area and spikelet number per panicle.Compared with other treatments under the IPN,the population light transmittance,and leaf area duration,crop growth rate at different growth stages was relative higher under D4 treatment,which led a larger total biomass.In addition,there were no significant differences in harvest index(HI)between D4 treatment and low density treatments(22.22×104hill·hm-2(D1)and 25.64×104 hill·hm-2(D2)),but HI under D4 treatment was larger than that of high density treatment(40×104 hill·hm-2(D5)).The larger total biomass and HI led to a higher grain yield under D4 treatment.Moreover,the trend of DMT,dry matter translocation effeciency(DMTE)and the contribution of DMT to rice yield(CDMT)under different planting density treatments in the IPN were low density treatments(D1 and D2)>medium density treatments(D3 and D4)>high density treatment(D5).The dry matter accumulation after heading(DMAH)increased with the increasing planting density,and DMAH had a greater effect on rice yield than DMT under different planting densitity treattments in the IPN.This indicated that the DMT,DMTE and CDMT were more appropriate,and the DMAH was relative larger under D4 treatment than those of other treatments,which were beneficial to yield formation.In addtion,the total N accumulation gradually increased with increasing planting density,and the total N accumulation was relative larger under D4 treatmet.The changes of N translocation(NT)and N translocation efficiency(NTE),and the contribution of N translocation to grain(CNT)were not obvious under different planting density treatments.No significant differences were found in N production efficiency at different planting density treatments.The highest value of N partial production were observed at the D4 treatment.3.Effects of nitrogen application on rice grain yield formation in rice under the IPN.Compared with 7:3 and 8:2 treament(the ratio of base and tillering fertilizer to panicle fertilizer was 7:3 and 8:2),higher light transmittance,total biomass,panicle partitioning index and harvest index were observed under 6:4 treatment(the ratio of base and tillering fertilizer to panicle fertilizer was 6:4),leading to a laiger rice yield.The changes of yield components at different nitrogen application treatments under the IPN were showed that the effects of nitrogen application on panicle number per unit area,seed-setting rate and 1000-grain weight were not significant,while spikelet number per panicle under 6:4 treatment was higher than that of 7:3 and 8:4 treatment.This led a highest grain yield under 6:4 treatment than than that of 7:3 and 8:4 treatnent.Moreover,compared with NIPN,with the increasing panicle fertilizer,N,P,K accumulation of panicle and total N,P,K accumulation at maturity,as well as N,P,K partial factor production and N,P,K harvest index gradually increased,which were beneficial to yield formation.