| The current farming system is heavily reliance on chemical fertilizer(CF),which adversely affects soil health,the environment,and crop productivity.Recently the most challenging issue is to increase cereal grain yields and quality on sustainable basis to feed the growing population at the lowest environmental cost.Organic manure is an alternative source of fertilizer for compensating the CF requirements and also considered as eco-friendly.Although the advantages of organic manure fertilization are generally recognized,however the optimal substation ratio remains unclear.The objective of this study was to assess the combined effects of cattle manure(CM)and poultry manure(PM)with CF on soil properties,morpgo-physiological traits,nitrogen(N)metabolism,starch metabolism,and quality and productivity of rice.Two consecutive double-seasons experiments,pot(2018)and field(2019)were conducted at the experimental station of Guangxi University,Nanning,China during the early(March to July)and repeated during late(July to November)growing season.The study consisted of six treatments of organic manure and CF ratios,i.e.T1-CF0;T2-100%CF;T3-60%CM+40%CF;T4-30%CM+70%CF;T5-60%PM+40%CF,and T6—30%PM+70%CF to provide a pool N of 300 and 150(Kg ha-1)for pot and filed experiment,respectively.This study sought to elucidate how combined organic and chemical N fertilization affect soil properties,i.e.physical(soil bulk density(BD),soil porosity,and soil moisture content(MC)),chemical(soil organic carbon(SOC),total nitrogen(TN),soil available N,phosphorous,potassium,and pH),and soil biological(soil microbial biomass C(MBC and soil microbial biomass N(MBN)),and rice plant parameters like root morphological features(i.e.root length,root surface area,average root diameter,and total root volume),leaf physiological attributers(leaf gas exchange(i.e.net photosynthetic rate,stomatal conductance,intercellular CO2 concentration and transpiration rate),chlorophyll contents(chlorophyll a and b content),and N-metabolizing enzymes,(nitrate reeducates(NR),glutamine synthetase(GS),glutamine oxoglutarate aminotransferase(GOGAT)activities),starch-metabolizing enzymes(i.e.sucrose synthase(SS),ADPG pyrophosphorylase(AGPase),soluble starch synthase(SSS),granule bound starch synthesis(GBBS),starch branching enzyme(SBE),starch disbranching enzyme(DBE)activities and their relevant isoforms gene expression,such asSUS4,AGPS2b,SSS1,GBSS1,GBSE11b,and ISA during grain filling period,N uptake,N use efficiency(NUE),dry matter(DM)and N accumulation,grain yield,and rice grain qualitative traits,such as starch content(SC)amylose content(AC),protein content(PC),gel consistency(GC),and gelatinization temperature(GT).Results showed that soil properties,leaf physiological attributes,biomass accumulation,starch-metabolizing enzymes activity and their expression of isofrom genes,yield and yield components,and qualitative traits of rice were significantly affected by the combined organic and inorganic fertilizers application in both pot and field experiments.The combined treatment T6 improved the net photosynthetic rate,panicle numbers,biomass accumulation,grain yield and AC of rice by 11 and 16%,12 and 16%,11 and 15%,and 9 and 1%in the early and late seasons,respectively,compared to the sole CF treatment T2 in pot experiment(2018).Similarly,in the field experiment(2019)the treatment T6 enhanced the leaf chlorophyll content by 11 and 13%,N uptake by13 and 15%,biomass by 13 and 16%,grain starch content by 10 and 12%and grain yield by 10 and 14%during the early and late seasons,respectively,compared to T2.However,T4 was statistically(p<0.05)similar with T6.Likewise,the combined treatments T3 and T5 also significantly improved the leaf photosynthetic efficiency,DM and N accumulation,and grain yield of rice,compared to the non-N treated plants.Improvements in these traits was the results of higher leaf physiological activity and plant N uptake due to improved soil properties,i.e.SOC,TN,MBC and MBN and BD under the combined organic and inorganic N fertilizer treatments.In-addition,the T6 increased N-metabolizing enzymes activity,including NR,GS and GOGAT by 10 and 13%,11 and 14%,and 8 and 12%,respectively,during the early and late growing seasons,than sole CF treatment T2.Further,higher starch-metabolizing enzymes activity,i.e.SS,AGPase,SSS,GBSS,SBE and DBE by 19 and 16%,9 and 13%,7 and 10%,7 and 9%,16 and 23%,and 7 and 10%were recorded in integrated treatment T3 during the early and late seasons,respectively,compared with T2.However,treatments T4,T5 and T6 were noted statistically non-significant with T3.Increases in starch-metabolizing enzymes activities were mainly due to their highly expressed isofrom genes,i.e.SUS4,AGPS2b,SSS1,GBSS1,GBSE11b,and ISA during grain filling.Further,the activities of SS,AGPase,SSS,GBSS,SBE and DBE were highly positively correlated with grain starch accumulation.Crop grain yield is highly dependent on yield components.In this study,the linear regression analysis showed that the panicle number(R2=0.77**)and spikelet panicle-1(R2-0.93**)were very positively associated with grain yield.Furthermore,post-anthesis DM and N accumulation also plays a vital role in higher rice grain yield as confirmed from the regression analysis of DM(R2=0.85**)and N(R2=0.80**)accumulation which were positively allied with grain yield.Enhancement in yields attributes and post-anthesis DM and N accumulation were highly positive correlated with improved plant N uptake and leaf physiological activity,which could maintain superior leaf photosynthetic ability,which further increases post-anthesis biomass accumulation.In-addition,root morphological attributes were found higher and strongly positive associated with N uptake,total biomass and grain yield of rice.This increment in root morphological attributes was mainly due to improved soil properties under the combined treatments.Further,RDA showed a strong correlation of grain yield with soil properties,showing a significantly higher correlation of soil microbial biomass C and N with the grain yield.Consequently,the underground and aboveground processes have made a significantly contribution to grain yield,and the combination of 30%N from cattle or poultry manure with 70%N from chemical fertilizer(urea)is a promising option in term of improving soil health and grain yield of rice.This work provides a sustainable fertilizer management plan to increase rice grain yield with high N recovery rate and improving soil health. |
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