Research On Soil Carbon And Nitrogen Distributions And Variation Mechanism In The Middle And Lower Reaches Of The Yellow River Under Typical Land Uses

Changes in ecosystem structure caused by land use change and agricultural activities, are one of the most important aspects of human influence on terrestrial ecosystem processes. Protection and enhancement of soil quality is the basis for building a healthy ecosystem, and is significant for stabilizing regional as well as global environments. The present study starts from the perspective of different patterns of land use, and go on to analyze the distribution and variation mechanism of carbon and nitrogen in farming areas under the combined influence of the Yellow River’s flood and human activities. In an area of 30 × 40 km2 between Kaifeng and ZhongMou, use is made of uniform sampling with the grid method; soil samples includes the soil surface(0-20 cm) and soil cross section(0-100 cm) sample, the soil profiles sampling interval being 20 cm, and the sampling depth being 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm, with samples of different types of land use in the region included. First, description is given of the statistical characteristics of the data of carbon and nitrogen content in surface soil and soil profiles, respectively. Based on the results of statistical characteristics, selection is made of appropriate simulation methods, the Kriging interpolation method in geostatistics is used in the analysis of carbon and nitrogen spatial distribution in soil. Secondly, via the relationship between the soil’s carbon and nitrogen content and other physiochemical properties such as the soil’s pH value and particle composition, we analyze the inherent relationship between them, as well as the impact of these factors on soil carbon and nitrogen. Through the variation of carbon and nitrogen on soil profiles and mutual relationship, revealed are the influence of soil properties, land use patterns, crop types, farming history, farm management practices, and other human disturbances, upon the transformation mechanism of carbon and nitrogen in soil. The research results show:(1)Density of organic carbon in soils varies in space. Content distribution: city > outskirts > agricultural areas. Content of active organic carbon: suburban> agricultural area > city. Non-active organic carbon: city> agricultural area> suburbs. Nitrogen content of the soils, on the whole, is low; total nitrogen, ammonium, nitrate have density variation in space. Compared with the results of the second soil survey, carbon and nitrogen content of the soils of the study area have raised.(2)In the soil profiles, TOC, AOC, and NOC gradually decrease from the surface to deep layers, dropping fast within a depth of 0-60 cm, but gently within the depth of 60-100 cm. Under different land uses, soil organic carbon content varies in the following order: orchard > farmland > woodland. Total nitrogen of the soil, ammonium nitrogen, and nitrate nitrogen have the highest content in the surface soil, and the content of each decreases with increasing depth. The content of ammonium nitrogen is, in all the layers, less than that of nitrate nitrogen, and with only minute changes. Total nitrogen content and nitrate nitrogen content fluctuate below the depth of 60 cm. Content of total nitrogen and nitrate nitrogen of the soils under different land use patterns: orchard > farmland > woodland. Topsoil ammonium nitrogen: orchard > farmland > woodland, there being different orders of in layers of other depths. Along with an increase in layer depth, organic matter content in the soil decreases, and so does carbon and nitrogen content. Organic matter decomposition and transformation on the surface soil provides only limited supply to soils at deeper layers, thus showing a vertical gradient.(3)The spatial distributions of TOC, AOC, and NOC each have a moderate spatial autocorrelation, while that of TN has a strong spatial autocorrelation. The high and low areas TOC, AOC, and NOC coincide to a certain extent with those of TN. East Kaifeng, southeast of the Zhongmou County, and the levee along the Yellow River are high value areas; large extended areas from the town of Yanminghu to the Xinghuaying farm are low value areas.(4)Soil in the surface layer is different from that on the profiles in soil pH value, in soil particle composition, and in soil carbon and nitrogen correlation. TOC, AOC, NOC, TN was extremely significantly positive-correlated with the soil’s silt content, and was extremely significantly negative- correlated with pH value and sand content. Ammonium nitrogen is significantly positive-correlated with TN and significantly negative-correlated with pH value. Relationship of nitrate nitrogen with other indices was not significant. Soil properties along the soil profiles have significant effects on ammonium nitrogen and nitrate nitrogen. For sandy soils, clay content and silt content are significant to enhancing soil carbon and nitrogen content.(5)For soils of different farming years, soil carbon content and nitrogen content increase with the extension of cultivation time. Deep down the soil profiles, this effect weakens, carbon and nitrogen content being influenced more by soil properties, soil formation processes and parent material sources. Putting straw back to the soil, applying organic fertilizer, and other conservatory farming procedures play a constructive role in maintaining carbon and nitrogen presence in the soil.(6)For surface soils under different crop types, there are significant differences in carbon and nitrogen content. Organic carbon content and activated carbon content have this distribution: wheat > garlic> peanuts, watermelons > woodland. Distribution of soils’ total nitrogen content: wheat > garlic> woodland > peanuts, watermelons. Overall, the soil properties of wheat and garlic planting are closer, and those of peanuts, watermelons and woodland are closer.