Effects Of Combined Application Of Organic And Inorganic Fertilizers On Soil Organic Carbon Fractions,Aggregates And Crop Yield Under Different Land Use Patterns

Lou soil and dark loessial soil are the two main soil types distributed in the Guanzhong Plain and Weibei dryland of Shaanxi Province.At present,the main utilization methods are farmland and orchard.For a long time,the fertilization of these two soils has been mainly based on chemical fertilizers.However,long-term and large-scale application of chemical fertilizers has caused soil structure damage and increased organic carbon mineralization,resulting in a decline in soil quality and seriously restricting the sustainable development of local agriculture.In view of the above problems,this paper takes the Lou soil in the Guanzhong Plain and the dark loessial in the Weibei dryland as the research object,and selects two land use modes of farmland and orchard,after three years of chemical fertilizer（NPK）and organic and inorganic fertilizer（NPKM）treatment,the effects of different fertilization and utilization methods on soil organic carbon and its components,aggregate distribution and stability,and crop yield changes were studied.The relationship between soil organic carbon-soil structure-crop yield was analyzed,which provided theoretical support for increasing soil fertility,improving soil structure and increasing crop yield of Lou soil and dark loessial soil.The main results are as follows:（1）Fertilization and land use had significant effects on soil organic carbon and its components and distribution ratio.Compared with NPK,NPKM treatment increased the contents of soil organic carbon（SOC）,soil microbial biomass carbon（MBC）,soil labile organic carbon（LC）and recalcitrant organic carbon（RC）.In Lou soil,NPKM mainly increased the values of MBC/SOC and RC/SOC at 0-20 cm and 20-40 cm depths,effectively promoted the improvement of soil fertility,and the increase of SOC content in farmland soil was greater than that in orchard soil.In dark loessial soil,NPKM treatment increased the value of MBC/SOC at 0-20 cm and 20-40 cm depths and the proportion of recalcitrant organic carbon in 0-20 cm soil layer,promoted the increase of surface soil fertility and the stability of soil organic carbon,and the increase of SOC content in farmland soil was less than that in orchard soil.For Lou soil,the contents of SOC,MBC,LC and RC in farmland soil were higher than those in orchard soil.It mainly increased the value of RC/SOC and promoted the increase of organic carbon stability.For dark loessial soil,farmland soil reduced organic carbon and its components,and increased the values of MBC/SOC and LC/SOC.Correlation analysis showed that there was a significant positive correlation between soil organic carbon content and MBC,LC and RC content.（2）Fertilization and land use patterns have certain effects on the distribution and stability of soil aggregates.Compared with NPK,NPKM treatment showed an increasing effect on>2 mm and 2-0.25 mm aggregates,mean weight diameter（MWD）,geometric mean diameter（GMD）and>0.25 mm aggregate content(R_0.25)in 0-20 cm soil layer in Lou soil and dark loessial soil,effectively improving soil structure and promoting the stability of surface soil aggregates.Under different land use patterns,the increase of MWD of farmland soil aggregates in Lou soil was greater than that in orchard soil,while the increase of MWD of orchard soil in dark loessial soil was greater than that in farmland soil.For Lou soil,the content of>2 mm and 2-0.25 mm aggregates,MWD and GMD were increased in farmland soil compared with orchard soil,which promoted the stability of soil aggregates.In dark loessial soil,the content of>2 mm,2-0.25 mm aggregates and MWD,GMD showed orchard>farmland.Correlation analysis showed that MWD,GMD and R_0.25of soil aggregates were significantly positively correlated with the content of>2 mm and 2-0.25mm aggregates,but negatively correlated with fractal dimension（D）.（3）The organic carbon content of aggregates increased with the increase of particle size,and decreased with the increase of soil depth.Compared with NPK,NPKM treatment promoted the increase of organic carbon and labile organic carbon content in aggregates of0-20 cm and 20-40 cm soil layer in both Lou soil and dark loessial soil,and increased the contribution rate of organic carbon in>0.25 mm aggregates,which was beneficial to the physical protection of aggregates to organic carbon and promoted the accumulation of organic carbon.Relatively speaking,the increase in the content of organic carbon and labile organic carbon within>0.25 mm aggregate fraction in Lou soil was greater in farmland than in orchards,while in black loam soil,the main increase was in<0.053 mm silty-clay organic carbon,with the increase being greater in farmland than in orchards.For Lou soil,compared with orchard soil,farmland soil increased the content of organic carbon and labile organic carbon within>0.25 mm large aggregate fractions in 0-20 cm and 20-40 cm soil layer,and reduced the contribution rate of organic carbon within 0.25-0.053 mm micro-aggregate fractions and<0.053 mm silty-clay in each soil layer.Farmland is more conducive to the recovery and consolidation of soil organic carbon.While for the dark loessial soil,compared with orchard,the farmland soil reduced the organic carbon and labile organic carbon content in aggregates of 0-20 cm soil layer,and increased the contribution rate of<0.053 mm silty-clay organic carbon.Orchard was more conducive to the recovery and consolidation of surface soil organic carbon,and organic carbon mainly concentrates towards silty-clay.（4）Compared with NPK,NPKM significantly increased the yield of wheat,maize and apple,and the soluble solids and fruit hardness of apple in the two soils.The increase of wheat yield in Lou soil was larger than that in dark loessial soil,while the increase of apple yield,soluble solids and fruit hardness was smaller than that in dark loessial soil.NPKM treatment also increased the photosynthetic rate of wheat,maize and apple at different growth stages,and the photosynthetic rate of wheat and maize at filling stage and apple at fruit coloring stage increased significantly.The growth and yield of crops are affected by soil organic carbon components and soil structure.For farmland,SOC is the main factor affecting crop yield and photosynthetic rate.For orchards,MBC and SOC were the main factors affecting apple yield and photosynthetic rate.In conclusion,the combined application of organic and inorganic fertilizers is conducive to improving soil fertility,improving soil structure,increasing the content of organic carbon in large aggregates and the contribution rate of organic carbon,which is conducive to improving the physical protection of organic carbon by aggregates,and also improving crop yield and apple quality.For Lou soil,farmland increased the content of soil organic carbon and its components and improved soil structure compared with orchard.For dark loessial soil,the orchard is better than the farmland in promoting soil carbon sequestration.Therefore,combined application of organic and inorganic fertilizers is an effective measure to improve soil organic carbon and maintain soil structure.The transformation of farmland to orchard in dark loessial soil area is conducive to the maintenance and improvement of soil organic carbon.