Effect Of Combined Application Of Organic And Inorganic Fertilizers On Crop Growth And Soil Fertility In A Rice-wheat Rotation System

Chemical nitrogen?N?fertilizers were always over applied nowdays in China,which could lead to a low N use efficiency and a seriously environmental pollution.Therefore reduced chemical N fertilizer application while still keeping a sustainable crop yields has been and still will have been the hot issue in the field of soil science and plant nutrition.Field experiments were carried out so as to study the effects of the combined application of pig manure compost and chemical N fertilizers on crop yields,dry matter accumulation and nutrient accumulation and on the soil fertilities,such as soil aggregates,contents of soil nutrients and organic matter,and soil microbial diversity.The designed experiment consitsted of 5 levels of N application rates(0,180,240,270 and 300 kg·N·hm^-2)and 3 levels of manure composts(1500 kg·hm^-2,3000 kg·hm^-2,4500 kg·hm^-2)applied.The main results obtained were listed as follows.1.Yields of rice and wheat grains were significantly increased under the combined application of chemical fertilizer and compost treatments.The yield of rice and wheat grains under combined application of 180 kg·N·hm^-2 and 3000 kg·hm^-2 compost or combined application of 240 kg·N·hm^-2 and 4500 kg·hm^-2 compost,for examples were significantly higher than in chemical fertilizer alone treatments.The rice grain yields were on average increased by 1.1%-11.8%under the combined application 240 kg·N·hm^-2,300 kg·N·hm^-2 with compost,as compared to chemical fertilizer alone treatment.The above ground dry matter weight of rice plants under the treatments of combined application of 180 kg·N·hm^-2 and 3000 kg·N·hm^-2 compost;combined application of 240 kg·N·hm^-2 and 4500 kg·hm^-2 compost;combined application of 240 kg·N·hm^-2 and 4500 kg·hm^-2 compost;combined application of 300 kg·N·hm^-2 and 1500 kg·hm^-2 compost were significantly increased as compared to chemical fertilizer alone treatments.The difference was not significant in wheat season.The sustainable yield index?SYI?were higher under the treatments of combined application of chemical fertilizer and compost than chemical fertilizer alone treatments when 240 kg·N·hm^-2 or 270 kg·N·hm^-2 were applied.2.The aboveground N accumulation of rice plants under the treatments of combined application of 180 kg·N·hm^-2 and 4500 kg·hm^-2 compost;combined application of 240 kg·N·hm^-2 and 3000,4500 kg hm"2 compost;combined application of 270 kg·N·hm^-2 and 4500 kg·hm^-2 compost were significantly increased as compared to chemical fertilizer alone treatments.There was no significant difference between the treatment of combined application of chemical fertilizer and compost and chemical fertilizer alone treatment when N application rate was 300 kg·N·hm^-2.The influence was not significant at wheat season.The influence of different treatments on N use efficiency were consistent with the influence of different treatments on the aboveground N accumulation in both seasons.3.The combined application of chemical fertilizer and compost significantly increased the mean-weight diameter?MWD?and geometric-mean diameter?GMD?.The proportion of>2 mm fractions for wheat season,and>0.5 mm fractions for rice season were significantly higher than chemical fertilizer alone treatment.The proportion of<0.05 mm fractions in combined application of chemical fertilizer and compost treatments decreased for both seasons.The proportion of>2 mm fractions,1-2 mm and 0.5-1 mm for wheat season was significantly higher than rice season.4.The combined application of chemical fertilizer and compost significantly decreased the density of soil,and significantly increased soil total N,total P,total K,available N,available P,and available K as compared to chemical fertilizer alone treatments.Combined application of chemical fertilizer and compost significantly increased the concentration of nitrate and ammonium in the top soil?0-20 cm?and decreased the concentration of nitrate and ammonium at soil depth of 20 cm to 100 cm.5.Combined application of chemical fertilizer and compost increased the C proportion to>2 mm fraction in wheat season and C proportion to>2 mm fractions,1-2 mm and 0.5-1 mm in rice season.The C proportion of 1-2 mm for rice season soils was significantly higher than that in wheat season.Compost application increased the KMnO4 oxidizable labile organic carbon?LOC?proportion to>2 mm fraction in wheat season soils and the LOC proportion of>2 mm fractions and 1-2 mm in rice season soils.The content of free light fraction under combined application of chemical fertilizer and compost treatments were higher than that of chemical fertilizer alone treatment for both crop seasons,and the content of heavy fraction under combined application of chemical fertilizer and compost treatments were lower than that of chemical fertilizer alone treatment for wheat season.The percentages of alkyl C and carboxyl C in combined application of chemical fertilizer and compost and compost alone treatments were higher than those in chemical fertilizertreatment,while the percentages of O-alkyl C were less than those in NPK treatment.Thehydrophobicities of compost treatments were also high as compared to those of chemicalfertilizer alone treatment.6.Combined application of chemical fertilizer and compost changed the microbialproperty at harvest of the two crop seasons.The soil microbial biomass in combinedapplication of chemical fertilizer and compost treatments was higher than of chemicalfertilizer alone treatment in both rice and wheat seasons and the difference was significant.The soil bacterial community diversity and richness index in combined application ofchemical fertilizer and compost treatments were significantly higher as compared to thosein chemical fertilizer alone treatment,while fungal community diversity and richness indexin combined application of chemical fertilizer and compost treatments were decreased.Pyrosequencing data of bacterial community showed that the dominant phyla for riceseason soils were Acidobacteria,Proteobacteria and Firmicutes,while they wereAcidobacteria,Proteobacteria,Actinobacteria,Bacteroidetes and Chloroflexi for wheatseason soils.Combined application of chemical fertilizer and compost increased theabundance of Actinobacteria,Chlorobi,Proteobacteria,and decreased the abundance ofAcidobacteria,Chloroflexi,Firmicutes,Nitrospirae.Pyrosequencing data of fungalcommunity showed that the dominant phyla for rice season were Ascomycota andGlomeromycota,while for wheat season the dominant phyla were Ascomycota.The soilmean-weight diameter?MWD?was significantly related to soil fungal community.Combined application of organic fertilizer and chemical fertilizer could significantlyincrease the abundance of ammonium oxdising bacteria in top soil,as compared tochemical fertilizer alone treatment.Conclusion:In the typical region of rice-wheat rotation system in southern Jiangsu province,a continued application of commercial organic fertilizers?4500 kg-hm"2?could reduce thechemical N fertilizer application rate from 270 kg·N·hm^-2-300 kg·N·hm^-2 to 240 kg N-hm"2.This fertilizer application model could be considered as a better one because it couldsignificantly increase crop yields by increasing the contents of soil C and other nutrientsand improving the soil aggregates and soil microbial communities.