Effects Of Combined Application Of Organic And Inorganic Fertilizers On Soil Organic Carbon And Fertility In Reclaimed Rural Homestead Soil

The experiment was conducted in the experimental base of a cultivated land quality monitoring point in Hanjiang Gongdao Town,Yangzhou City,from 2021 to 2022 to investigate the impact of the combined application of organic and inorganic materials on soil fertility and organic carbon in rural homestead reclamation.Urea,calcium superphosphate and potassium chloride were used as inorganic fertilizers,and chicken manure,earthworm manure and rapeseed cake fertilizer were used as organic fertilizers.The experiment was carried out in a randomized block design with three replicates.Five treatments were set up:(1)T0:no nitrogen fertilizer,(2)T1:100%chemical fertilizer N,(3)T2:40%chicken manure N+60%chemical fertilizer N,(4)T3:40%earthworm manure N+60%chemical fertilizer N,(5)T4:40%rapeseed cake fertilizer N+60%chemical fertilizer N.The soil comprehensive nutrients,soil enzyme activities,soil aggregates,soil organic carbon mineralization,soil organic carbon components and humus components were measured in different soil layers(shallow 0-15 cm,deep 15-30 cm).The effects of organic and inorganic fertilizers on organic carbon and soil fertility in rural homestead reclamation were clarified in order to provide theoretical support for soil fertility in rural homestead reclamation.The main results are as follows:1.Soil physical and chemical properties,enzyme activity:(1)In the 0-15 cm soil layer,compared with the single application of chemical fertilizer,the combined application of organic and inorganic fertilizers increased the soil pH value,reduced the bulk density,and increased the contents of soil organic matter,total nitrogen,available nitrogen,available phosphorus and available potassium.The increase ranges were 3.19～23.5%,7.00～15.6%,10.4～17.7%,1.60～22.9%,7.1～19.7%(2021)and 6.96～24.7%,10.0～31.9%,15.8～22.5%,7.39～31.9%,8.92～25.1%(2022).Among them,earthworm manure and rapeseed cake fertilizer are more conducive to improving soil nutrient index content;the activities of soil urease,sucrase and lipase were improved,and earthworm manure and rapeseed cake fertilizer were more conducive to improving soil enzyme activity.(2)In the 15-30cm soil layer,compared with the single application of chemical fertilizer,the combined application of organic and inorganic fertilizers increased soil pH value,reduced bulk density,increased soil organic matter,total nitrogen,alkali-hydrolyzed nitrogen,soil urease,sucrase and lipase activity,but had no significant effect on available phosphorus and available potassium.Among them,vermicompost and rapeseed cake fertilizer were more conducive to improving soil nutrient index content,chicken manure was more conducive to improving urease and sucrase activity,and vermicompost was more conducive to improving lipase activity.(3)The soil bulk density of 15-30cm was higher than that of 0-15 cm,but the contents of organic matter,total nitrogen,alkali-hydrolyzable nitrogen,available phosphorus and available potassium in 15-30cm were lower than those in 0-15cm.2.Soil aggregate distribution,stability and aggregate carbon and nitrogen content,organic carbon mineralization:(1)0-15cm,>2mm,0.25-2mm and<0.25mm the mass ratio of each particle size aggregates,0.25-2mm aggregate mass ratio is the largest;compared with the single application of chemical fertilizer;the combined application of organic and inorganic fertilizers increased or significantly increased the mass ratio of 0.25-2mm aggregate content and soil stability parameters(MWD,GMD and R0.25)by 11.8～27.4%,4.29～12.9%,8.00～16.0%,4.73～10.2%(2021)and 13.3～30.1%,7.25～14.5%,10.4～20.8%,7.16～14.0%(2022),respectively,among which rapeseed cake fertilizer increased the most;the contribution rate of 0.25-2mm aggregates to carbon and nitrogen nutrients was greater than that of other aggregates.The soil mineralization rate,potential mineralizable organic carbon and cumulative mineralization were significantly increased in the combined application of organic and inorganic fertilizers,with the most significant increase in rapeseed cake fertilizer and earthworm manure.(2)15-30cm,the mass ratio of<0.25mm aggregates was the largest.Compared with the single application of chemical fertilizer,the combined application of organic and inorganic fertilizers maintained or increased the mass ratio of>2mm and 0.25-2mm aggregates,but reduced the mass ratio of<0.25mm aggregates and improved the stability of soil aggregates.The contribution rate of<0.25 mm aggregates to carbon and nitrogen nutrients was greater than that of other aggregates.The trend of soil mineralization rate,potential mineralized organic carbon and cumulative mineralization were similar to that of 0-15 cm.(3)Compared with 0-15cm,the proportion of>2mm and 0.25-2mm aggregates in 15-30cm soil layer decreased significantly,and the proportion of<0.25mm aggregates increased significantly.3.The changes of soil organic carbon and humus components:(1)In 0-15 cm,the contents of soil organic carbon components were increased by applying different types of organic and inorganic fertilizers.The proportions of soil microbial biomass organic carbon(MBC),soil dissolved organic carbon(DOC),soil readily oxidizable organic carbon(ROC)and soil particulate organic carbon(POC)were 1.18～2.29%,0.67～0.77%,25.8-39.0%and 20.5～41.7%,respectively.DOC increased the most with chicken manure.The content of humus increased by 11.6～18.8%under the combined application of organic and inorganic fertilizers.Humin,humic acid and fulvic acid were all significantly increased by earthworm manure.(2)15-3 0cm,the combined application of organic and inorganic fertilizers increased the content of soil organic carbon and humus components.Among them,earthworm manure increased the proportion of DOC and ROC and the content of fulvic acid most significantly.Chicken manure significantly increased the proportion of MBC and the humin and humic acid content.In summary,40%organic fertilizer combined with 60%inorganic fertilizer significantly improved reclaimed soil’s physical and chemical properties in rural homesteads,increasing soil enzyme activity,soil organic carbon and humus content.At the same time,this fertilization measure maintained or increased the content of 0.25-2mm particle size aggregates and the carbon and nitrogen contribution rate and strengthened the amount of soil organic carbon mineralization.Therefore,it is recommended to use rapeseed cake fertilizer combined with inorganic fertilizer for soil fertilization management measures in rural homestead reclamation soil.