Nitrogen Enrichment And Ecological Risk Assessment Of Cropland Topsoil In Fujian By GIS Technology

In this Paper, taking Fujian Province as the study area, and use 1:50000 farmland use-soil type database and take 2021 points in the second soil census in 1982, and the soil fertility investigation of data in 2008 are 29945 samples, GIS and mathematical model of integration technology were employed, Systematic analysis differences of soil nitrogen enrichment under Prefectural-level city (district), with different farmland uses (vegetable piots, irrigated paddy fields, dry farmland, irrigated farmland and rain fed paddy fields) and different soil types level (Soil group) that influence the enrichment of nitrogen over the past 30 yeas, at the same time, the partition of the ecological risk of soil nitrogen enrichment was also ansnlyzed, The research results can provide theory basis for optimal management of nitrogenous fertilizer, agricultural non-point source pollution control and ecological environmental protection in Fujian Province. The research shows the results as follows:(1) In 1982 and 2008, the soil total nitrogen density and storage in cropland of Fujian province was 0.258 kg m-2 and 4.257 Tgrespectively, in 1982, and rose to 0.262 kg m-2 and 4.39 Tg respectively, in 2008. In 1982 and 2008, the areas which the higher nitrogen content were distributed mainly over Longyan, Nanping, Ningde and Sanming, and the distribution of higher nitrogen storage were Nanping, Sanming, Longyan and Ningde. In 1982 and 2008, the total nitrogen density of rain fed paddy and irrigation paddy field were relatively high, and the total nitrogen storage of irrigated paddy field were relatively high. In 1982, the soil groups which the total nitrogen contents were higher than the average level (0.258 kg m’2) of the province were purplish soils, calcareous soils, yellow soils, red soils and paddy soils; in 2008, the total nitrogen contents were higher than the average level (0.262 kg m"2) of the province were red soils, yellow soils, paddy soils and purplish soils; total nitrogen storage of paddy soils were the largest in 1982 and 2008.(2) Between 1982 and 2008, the soil total nitrogen in the cropland showed an enrichment trend. The nitrogen enrichment areas accounted for 52.49% of the total cultivated land in Fujian. Nearly 30 years, the enrichment degree of farmland total nitrogen in Longyan, Nanping, Sanming and Quanzhou of Western, central section, northern and southeast in Fujian were significant. The enrichment degree of rained paddy and paddy fields were the most significant, and the most significant soil group was Fluvo-aquic soils, the largest size of soil groups which enriched nitrogen was paddy soil.(3) In 2008, the total cultivated area of the ecological risk of enriched nitrogen accounted for 20.9% of the total area the cultivated land in Fujian, which meant there were some ecological risks caused by the nitrogen enrichment, which shows that a part of the cultivated soil existed a certain ecological risk in Fujian. The proportion of low ecological risk was the main part, accounted for 51.21%; The bigger potential ecological risk of farmland by the nitrogen enrichment was mainly distributed in Longyan, Nanping and Sanming. The ecological risk of Irrigation paddy field was bigger than soil types. The main ecological risk was paddy soils, and the soil subgroups was percogenic paddy soils.