Characteristics Of Soil Organic Carbon,nitrogen And Its Fractions Under Different Land Use In The Yihe River Basin

Soil organic carbon,nitrogen and its fractions,as important components of soil carbon and nitrogen pools,can provide necessary nutrients for plants and play an important role in maintaining the balance of the soil ecosystem.Different land use leads to different surface cover and soil internal conditions,which affect the contents of soil organic carbon,nitrogen and its fractions.The Yihe river basin was located in the rocky mountain areas of northern China.The complex and undulating terrain and serious rainfall erosion in the basin lead to thin local soil layer and poor soil quality.Taking the Yihe river basin as the research area,this thesis studied the differences of soil organic carbon,nitrogen and its fractions and C: N ratio under different land use.The sensitivity,correlation,and spatial distribution characteristics of soil organic carbon,nitrogen and its fractions in the basin were further analyzed.The effects of soil texture,soil type,soil parent material,terrain(altitude,slope direction,slope),climate(temperature and precipitation)on soil organic carbon,nitrogen and its fractions were discussed.It was expected to to provide fundamental data and scientific guidance for optimizing land use structure,land management and soil productivity.The main conclusions are as follows:(1)In soil surface(0～20 cm),the contents of soil organic carbon,nitrogen and its fractions were significantly higher in forest land and grassland than in cultivated land and garden land.Under different land use,the contents of SOC,TN,LFOC,and HFOC were higher in forest land,followed by grassland,cultivated land,and garden land.PON content was higher in forest land,followed by grassland,garden land,and cultivated land.The contents of ROC and DOC were greater in grassland,followed by forest land,cultivated land,and garden land.POC,HFOC,and HFON contents were abundant in grassland,followed by forest land,garden land,and cultivated land.Under different land use,the amounts of soil organic carbon,nitrogen and its fractions exhibited obvious surface aggregation.In the vertical direction(0～40 cm),the contents and the significance of difference decreased with increase in soil depth.At 0～40 cm soil layer,the ratios of the SOC: TN,POC: PON,LFOC: LFON and HFOC: HFON were higher in grassland and forest land than in garden land and cultivated land.The POC: PON and LFOC:LFON ratios were higher than the SOC: TN ratio,but the HFOC: HFON ratio was lower than the SOC: TN ratio under the same land use.(2)The sensitivity of soil active organic carbon and nitrogen fractions in the Yihe river basin was higher than that of SOC and TN,respectively.In comparison,the sensitivity of HFOC and HFON was lower than that of SOC and TN,respectively.The sensitivity of POC and PON was the highest in the soil organic carbon and nitrogen fractions,respectively.There was a significant positive correlation(P<0.01)between soil organic carbon,nitrogen and its fractions.The internal correlation between the contents of soil organic carbon and nitrogen was strong.(3)The spatial correlation of soil organic carbon,nitrogen and its fractions in the Yihe river basin was generally weak.The spatial variation was dominated by random variation.It was greatly affected by human activities such as agricultural production and soil and water conservation in the basin.Soil organic carbon,nitrogen and its fractions had extremely uneven spatial distribution.The contents of ROC and HFON differed significantly from the east to the west,and the contents of POC,LFOC,and PON varied significantly from the north to the south.The contents of soil organic carbon,nitrogen and its fractions were generally higher in the north of the basin(Yinan county,the junction of Yinan county and Yishui county,the junction of Yinan county and Fei county),but generally lower in the southwest of the basin(Pingyi county).(4)Soil texture,soil type,soil parent material,climate,and topography affected the spatial distribution of soil organic carbon,nitrogen and its fractions in the Yihe river basin.Under different soil texture,the contents of POC and PON were higher in sandy loam,and the contents of other indicators were higher in silty clay loam and silt.Under different soil types,the order of PON content was cinnamon soil,coarse bone soil,and brown soil,and the other indicators were cinnamon soil,brown soil,and coarse bone soil.Under different soil parent materials,the order of POC content was sand shale,limestone,and granite,and the other indicators were sand shale,granite,limestone.The contents of soil organic carbon,nitrogen and its fractions were negatively correlated with temperature but positively correlated with precipitation.As altitude and slope increased,the contents of soil organic carbon,nitrogen and its fractions increased in fluctuation.Human activities mainly influenced the fluctuation.The contents of soil organic carbon,nitrogen and its fractions were higher in the shady,and semishady slopes than in sunny and semi-sunny slopes.