| Red soil region in southern China is an important agricultural production base, with land area only of 1/5, but raising 40% of the population. With the increase of modern agricultural inputs, the influence of non-point source pollution in the environment caused by agricultural production and rural life has become increasingly prominent. In Qiyang County, Hunan Province, we investigated farmland field area and collected related information, and collected a large number of soil samples by using GPS. Compared with the results of long-term fertilization experiment, we discussed the temporal- spatial variability of soil nutrient, nutrient balance and estimated the nutrient loss to provide a scientific basis for the prevention and control of agricultural non-point source pollution. The main conclusions of this paper were as follows:1) Compared with the results of the Second Soil Census, almost all nutrients contents including OM, TN, available N and available P have increased in different levels, in which paddy field increased by 9.6%, 17.4%, 23.4% and 46.5%, respectively, and upland field increased by 13.6%, 8.3%, 6.1% and 49.4%,respectively. Available K decreased sharply by 18.4% in paddy field and by 24.1% in upland field. In different soil profile, contents of OM and TN increased in all layers of paddy soil and upland soil; TP decreased in all layers of paddy and upland soil; TK decreased in cultivated horizon and plow pan in paddy field, and decreased in cultivated horizon and illuvial horizon in upland field. TK increased significantly in gley horizon of paddy field and parent material horizon of upland field. From thickness of soil layers, the depth of cultivated horizon and plow pan decreased 9cm and 8cm in paddy field, respectively, and in upland field, the depth of cultivated horizon decreased 5cm and illuvial horizon increased 4 cm .2) N and P were in surplus and K had a deficit in Qiyang county agroecosystem. Surplus amount of N was 194.63 kg·hm-2·a-1 ~243.44 kg·hm-2·a-1, and the average annual rate of profit is 89.20% in paddy soil. Surplus amount of N was 50.96 kg·hm-2·a-1 ~150.84 kg·hm-2·a-1 in upland field, and the rate of profit is 50.88%. Surplus amount of P was 2.86 kg·hm-2·a-1 ~32.35 kg·hm-2·a-1 and 26.63 kg·hm-2·a-1 ~39.98 kg·hm-2·a-1 in paddy soil and upland field,with the average annual rate of profit of 13.96% in paddy soil and 27.75% in upland soil, respectively. The deficit of K was 69.07 kg·hm-2·a-1 ~137.52 kg·hm-2·a-1 and10.32 kg·hm-2·a-1 ~164.69 kg·hm-2·a-1 in paddy soil and upland field,and the average annual rate of deficit is 34.55% and 29.07%, respectively.3) Through long-term different fertilization treatment test located in Qiyang County, we studied the effect of different fertilization treatment on the soil balance. In CK treatment, the supplying amount of N, P and K were 21.43 kg·hm-2·a-1, 10.72 kg·hm-2·a-1, 31.71 kg·hm-2·a-1, respectively. The amount of nutrients absorption declined year by year, and N, P and K nutrients in soils were depleted greatly. With inorganic chemical treatment, soil nutrition balance had increased, and surplus amount of N was 211.88 kg·hm-2·a-1 ~254.17 kg·hm-2·a-1. With NPKM treatment, the contents of soil TN, TP and TK in plough layer improved, and the amount of nutrients absorption increased and soil nutrients kept balance on the whole as an ideal fertilizer treatment.4) The amount of N loss in farmland at Qiyang County was 26933.10t,including leaching amount of 362.72t, ammonia volatilization of 26141.6t, and nitrification-denitrification loss of 428.78t. The amount of P loss was 3.30t, including leaching amount of 2.64t, and runoff amount of 0.66t. The amount of K loss was 507.81t, including leaching amount of 422.08t, and runoff amount of 85.73 t. The loss of these nutrients was not only a serious waste of limited resources, but also increased the production cost of agriculture, and reduced the overall efficiency of agriculture, which may be a major reason to non-point source pollution.From the above, we should reduce the use of chemical fertilizers,and increase the amount of organic manure fertilizer application to improve soil fertility and nutrient storage capacity, reducing the loss of Nitrogen and Phosphorus in the environment for building high-yield crops and resource-saving environment-friendly agricultural development mode. |
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