Effect Of Adding Exogenous Calcium And Organic Materials On The Transformation Of Soil Organic Carbon

Facility agriculture is an important means of increasing agricultural efficiency and increasing farmers income.China has become the country with the largest facility cultivation area in the world.During the cultivation of the facility,strong evaporation and transpiration make the acidification of the soil accompanied by the accumulation of a large amount of excess fertilizer,leading to degradation of the facility soil.In order to improve the acidification of facility soils,Ca O is often used in production practice.The soils of Liaoning,Shandong Shouguang,Ningxia and other facilities found that the salt segregants were mainly Ca²⁺,and the content was significantly increased compared with the open soil.Calcium is not only an essential element for plant growth and development,but also plays a role of bond bridge in the formation of soil aggregates.Soil aggregates are the main place for soil organic carbon.Related studies have been carried out on the effects of calcium on soil organic carbon conversion.Under the special environmental conditions of facility cultivation,the process of soil organic carbon conversion and accumulation is quite different from that of open soil.But there are relatively few studies on the effects of calcium on organic carbon in facility soils.With the intensification of soil degradation in facilities,people pay more and more attention to the changes of soil organic carbon content in the facility and its relationship with soil physical and chemical properties.Therefore,the paper takes the continuous cultivation of soil for 10 years as the research object.Using indoor constant temperature simulation culture method,Exogenous calcium and four organic materials were added to detect and analyze the CO₂ emission and the content of different organic carbon in the culture process.The research results provide a theoretical basis for rational fertilization in facility cultivation.The main findings are as follows:（1）The release of calcium chloride and the application of biochar and coke were inhibited by the release of CO₂ from the soil,while the single application of calcium oxide and the combination promoted the release of CO₂ from the soil,and on the 172th day of culture,the cumulative release of CO₂ treated with calcium oxide alone increased by 34.12%compared with the control.The combination of two exogenous calcium with rice and corn stalk inhibited the release of CO₂ from the soil,at the 172th day of culture,the cumulative release of CO₂ from rice straw and exogenous calcium decreased by 21.02%and 54.82%compared with single application,corn stalks were reduced by 12.79%and 62.78%,and the inhibition of calcium chloride was greater than that of calcium oxide.（2）The cumulative release of CO₂ in soils treated with organic materials and calcium chloride was consistent with Ft=F0(1-e^-kt).The results show that the addition of calcium chloride can reduce the mineralization potential of soil organic carbon and enhance the carbon sequestration capacity of soil organic carbon.The treatment related to calcium oxide is in accordance with Yt=Y0-a*e^-bt,and the fitting results show that the addition of calcium oxide can promote soil organic carbon mineralization.（3）The total organic carbon content of the added calcium oxide soil decreased by 18.91%compared with the control at the 24th week of culture,while the addition of calcium chloride increased by 16.39%.The total organic carbon content of different organic materials and calcium oxide combined with soil was higher than that of the single application at the 8th week,and with the cultivation,at the 24th week,corn stalk,biochar and peat were combined with calcium oxide.The application was reduced by 25.21%,23.01%and 29.29%,respectively,the combined application with calcium chloride decreased by 23.11%,4.52%and 15.16%,respectively.（4）Addition of exogenous calcium increased soil soluble organic carbon content.At the24th week,calcium oxide and calcium chloride increased by 71.07%and 19.46%,respectively.Compared with single application,rice straw,corn stover,biochar and grass charcoal and calcium fertilizer also increased soil soluble organic carbon content.Compared with calcium oxide at the 24th week,the application of calcium oxide increased by 74.00%,56.01%,76.33%and 121.83%,respectively;and the calcium chloride combined application increased by41.03%,40.04%,54.24%and 47.62%,respectively.（5）The application of exogenous calcium reduced the soil microbial biomass carbon content.At the 24th week of culture,the single application of calcium oxide and calcium chloride decreased by 13.81%and 12.50%,respectively,and the effect of adding calcium oxide is greater than that of calcium chloride.The soil microbial biomass carbon was higher than that of single application in the late application of different organic materials and calcium oxide,among them,the combination of rice straw and calcium oxide increased the most,and increased by 39.39%in the 24th week of culture,the combination of different organic materials and calcium chloride reduced the soil microbial biomass carbon.（6）Single application of exogenous calcium increased the amount of humus acid carbon in the soil.At the 24th week of culture,the two types of calcium were increased by 11.51%and43.31%,respectively.Except for rice straw,the application of organic materials after exogenous calcium and other organic materials reduced the amount of soil humus acid carbon.The content of fulvic acid after rice and corn stover and calcium oxide were higher than that of single application organic materials at 4.69%and 20.77%,respectively,and increased by 10.13%and29.19%with calcium chloride.At the 24th week,the addition of calcium oxide and calcium chloride increased by 26.33%and 122.95%,respectively,and the amount of humic acid carbon in the soil was lower than that of single application.（7）The activity of calcium oxide on soil urease increased by 29.87%at the 24th week compared with the control.The invertase activity was reduced by 99.56%.The addition of calcium chloride increased the soil urease activity by 43.54%,however,soil catalase and sucrase were reduced by 28.21%and 91.49%,respectively.After application of exogenous calcium and organic materials,soil catalase and sucrase activities were lower than single application of organic materials.（8）The addition of calcium oxide increased soil p H and available phosphorus content,which increased by 1.14 units and 88.57%compared with the control at the 24th week of culture.The addition of calcium chloride had no significant effect on soil p H,but significantly increased the content of soil alkaline nitrogen,which was 118.22%higher than that of the control group at the 24th week of culture.The changes of soil p H and available nutrients of different organic materials and exogenous calcium were basically consistent with single application of calcium.