Temporal And Spatial Variation Of Soil Organic Carbon And Nitrogen Stoichiometry Of Topsoil In Agricultural Land—A Case Study Of Xinxiang,China

The research selects the main grain producing area of Henan Province-Xinxiang City as the research object,and organizes the basic data of soil,meteorology and agricultural production in the 1980 s and 2010 s in the region,introduces the theory of ecological stoichiometry,and applies classical statistics and spatial analysis methods.To study the carbon and nitrogen ecological stoichiometry of surface soils in agricultural land in the study area,aiming at revealing the spatial and temporal differentiation of carbon,nitrogen and other elements,and analyzing the main factors that limit the improvement of cultivated land potential,in order to protect the soil ecological environment and improve farmland management.Provide data support for measures and decision making.The research results are as follows:(1)In the past 30 years,the soil organic carbon and nitrogen reserves of Xinxiang agricultural land increased from 72769.14 t and 8643.73 t in 1980 s to 11533.01 t and 12377.95 t in 2010,respectively,with an increase of 58.08% and 43.20%.In this period,except Huixian,the carbon and nitrogen reserves of other counties(cities)increased in varying degrees,and the increase of both showed a very significant correlation(p < 0.01).(2)During the study period,soil organic carbon and nitrogen content increased by 60.47% and 50%,respectively,reaching 9.58 g.kg-1 and 1.02 g.kg-1,which were lower than the national average level of the same period(C:13.75 g.kg-1 and N:1.42 g.kg-1).The coefficient of variation decreased from 59.12% and 52.94% to 30.16% and 28.43% respectively;the average value of carbon-nitrogen ratio in 1980 s was 8.95,which increased by 4.69% and the coefficient of variation decreased from 27.826.83% to 9.43% in 2010.(3)The results of semi-variogram showed that the nugget effect of C,N and C/N ratios in 1980 s and 2010 were 31.23%,36.68%,49.76% and 21.07%,24.34% and 49.88% respectively,showing strong spatial correlation;the spatial distribution of C and N content was dominated by structural factors and significantly affected;and the spatial distribution of C/N ratio was co-operated by structural factors and random factors.In spatial distribution,the high-value areas of soil carbon and nitrogen content in the surface layer of agricultural land in Xinxiang are concentrated in the north and northwest of Huixian City,while the low-value areas are mainly distributed in most areas of Yanjin County and Yuanyang County,with a zonal distribution in the direction of "northeast-southwest".The C/N ratio tends to be concentrated and the spatial distribution difference is small.(4)In terms of soil types,the content of organic carbon in the two periods was as follows: paddy soil > cinnamon soil > shajiang black soil > fluvo-aquic soil > aeolian soil;the nitrogen content in 1980 s was paddy soil > cinnamon soil > shajiang black soil > aeolian soil,and in 2010 was paddy soil > cinnamon soil > shajiang black soil > fluvo-aquic soil > aeolian soil.In terms of agricultural land types,the organic carbon content in the two periods was orchard > rainfed cropland > irrigated land > paddy field;the nitrogen content in 1980 s was orchard > rainfed cropland > irrigated land > paddy field,and in 2010 was rainfed cropland > orchard > irrigated land > paddy field.