| Regarding organic carbon decomposition model of agricultural soils as the core, using database consisting of physics and chemistry characters of agriculture soils, meteorological information, production of crops from 1985 to 2000 and agriculture management in Jiangsu province, combining with Geographic Information System technique, the dynamics from 1985 to 2000 and distribution in 2000 of agricultural soils carbon in Jiangsu province was simulated and predicted. Based on these results, the distribution of agricultural soils carbon 2010 was predicted, and the importance of returning straw to soils was discussed.At first, the sub-model of external organic matter impact factor was modified. Nineteen residues were sampled from different organs with 13 plants, their initial Total Nitrogen content ranged from 4.0 g/kg to 35.2 g/kg, while initial Lignin content from 157.7 g/kg to 254.0 g/kg and the variation is relatively uniformity. The relation of plants chemical content and their dynamic decomposition were investigated by an incubation experiment with 19 plant residues plus soil under 25 C and water content of 400 g/kg air dried soil. Then quantitative relation of plant nitrogen and lignin content on the residue carbon decomposition was set up by a multiple stepwise regression method. The relation can be well quantitatively described by Fw=l50+1.496N-0.572L(R2=0.7990,p<0.001, n=17). The Y represents decomposition percentage. The N and L represent the initial contents of nitrogen and lignin for a given residue, respectively. The Y could be either the first-order decay rate (B0=3.51 X 10-2, B1=4.61 X 10-4, B2= -1.53 X10-4, R2= 0.812**, n=19), or the percentage of CO2-C released over the 9-week period (B0=100, B1 =0.974, B2= -0.364, R2= 0.828**, n=19), or the percentage of weight loss over the 23-week period in the field burying experiment (B0=150,B1=1.496, B2= -0.572, R2= 0.799**, n=17). The percentage of easily decomposition has a positive relation with the initial nitrogen contents as a whole and a negative relation with the initial lignin.Secondly, in order to ensure this model could be applied totally in Jiangsu Province, data on soil fertilizer composting and organic matter contents of test points in Tongshan, Yixing, Danyang, Xinghua were collected. Four samples belong to traditional agricultural area of Xuhuai, Taihu, Ningzhen Hill, Lixia River respectively. The landing system andfarm rotation represent basically common situation utilization of soils in Jiangsu province. In addition, the initial organic carbon had distinct grads. The validation results showed that this model can greatly described the dynamic variation of soil organic matter. Furthermore, the simulative value was close to the real value, which means the simulative value can represent the real situation. Relative equation of 111 groups of simulated value and observed value was Y = 0.757X + 1.9545 (R2 = 0.6278** ), zero intercept equation was Y = 0.9656X (R2 = 0.5784** ) . The results of superficial stimulation of zero intercept equation could completely represent the real results.At last, based on model validation, we tried to combine model with GIS technique. Before using the technology, we only describe the situation in one period from tables or figures. Now, we can use GIS technology to describe the trends and process intuitionally. Using GRID format file and Visual Basic 6.0, the integration of models and GIS technique is realized. Simulation and prediction results indicated that the soil organic matter content in approximately 77% of the agricultural soils in Jiangsu province has been increased since the 2nd soil survey completed in the early 1980s. Compared with the values in 1985, the soil organic matter content in the 2000 was estimated to increase by 1.0-3.0 g/kg for the regions of northern Jiangsu and the coastal area, and 3.5-5.0 g/kg for the region of Tai lake in the southern Jiangsu. A slight decrease of 0.5-1.5 g/kg was estimated for the central section of Jiangsu and the Nanjing-Zhenjiang hilly area. Model predic...
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