| Due to the the unreasonable planting management in modern conventional agriculture such as highly intensive utilization and a large number of agricultural chemicals inputs, there are many negative effects on the ecological environment, including the deterioration of soil physical and chemical properties, eutrophication, the degradation of soil biological function, etc. The organic agriculture is an environment friendly way of agricultural production that respect natural ecological balance. It doesn’t use any chemical pesticide, chemical fertilizer or growth regulator in the process of planting, but rely on the biological organic fertilizers to meet the growing demand for nutrients, and adopt crop rotation, physical and biological measures to prevent and control disease, meanwhile. With the improvement of people’s living standards, organic agriculture in our country develops rapidly. Therefore, studying the characteristics of C, N, P fractions under organic agriculture has an important significance for understanding the eco-environmental effects, reducing the negative environmental impacts and promoting the healthy development of organic agriculture in our country. In this paper, through the survey of organic cultivation bases, comparative study was conducted of the soil fertility such as C, N, P, K and the characteristics of P fractions in organic and conventional agricultural soils. Furthermore, plot experiment in organic tea gardens was used to compare the characteristics of nutrient runoff losses in farmland and the greenhouse gas emissions between organic and conventional agriculture. The main findings are as follows:(1) The characteristics of soil fertility from organic and conventional management. Organic management increased the total nutrients of surface soil, while the available N was opposite. But the soil nutrients accordantly with soil depth between organic and conventional management, and with the extension of planting years in organic farming, the pH value was close to neutral. The average content of organic matter, CEC, total N, total P, available P, total K and available K in surface soil under organic management increased by 38.77%,12.30%,32.60%,18.58%,23.39%,12.05% and 50.77% compared with conventional management, respectively, but there was no significant difference. With the increase of soil depth, the nutrient content appeared a decreasing trend in profile from both management, but the content of organic matter, total N and available K reached significant level between the two management, while CEC, total P, available P and total K did not. Along with the extension of planting years in organic farming, the pH value was close to neutral, vegetable soil value changed from 6.51 to 6.79, paddy soil changed from 6.22 to 7.02, and tea soil changed from 3.81 to 4.56, both of them were close to 7.0.(2) The characteristics of P fractions from organic and conventional management. The constitute of P fractions under the two management were the same. It was the organic systems greater than the conventional systems of P content under different depths for each P fractions in soil, and the content tended to decline with the soil depths, the total P content is 53.45% higher in organic management than conventional management in 40-60 cm soil layer, especially. Along with the extension of planting years, the soil P turned to non-stable P gradually. The difference of crops also influenced to the P content and fractions. Non-stable P was the main body of soil P whether in organic management or conventional management that accounted for 56.23%～72.25% of total P, the second was medium labile P, accounted for 23.83%～27.56%, the least was labile P, accounted for 3.55%～16.74%. The distribution of each P fractions in soil was: the content of total P under organic management was 430.44～886.66mg/kg in 0-20 cm layer, while 20-40 cm layer was 318.75～793.73 mg/kg, and 40-60 cm layer was 293.68～683.88 mg/kg. It was 22.87%、23.70% and 53.45% higher than under conventional management respectively. The P fractions tended to become non-labile P with the growth of organic management ages extended, the main accumulation was Residual-P. There was no difference between organic and conventional management in the constitute of P fractions for paddy soils, tea soils and orange soils, but it could enhance the activity of soil P in vegetable soils under organic management. The content of P in crops was the conventional management bigger than organic management of all areas except for vegetable soils.(3) The characteristics of nutrient runoff losses in farmland from organic and conventional management. The trend of runoff in contrast, organic and conventional treatment were basically the same, the occurrence of runoff was concentrated in spring and summer. Organic management could reduce the concentration and amount of nutrient in runoff to some extent, but the trend of runoff in the three treatment was the same. Nitrate-N was the main loss fraction for nitrogen. Throughout the test period, the average concentration of total N, nitrate-N, ammonium-N, total P, total C and organic-C in runoff liquid under organic management was 17.85%,2.64%,24.05%,9.81%, 13.54% and 16.51% less than under conventional management, respectively. Nitrate-N was the main loss fraction for nitrogen, it accounted for 36.72%～54.44% of total N, while ammonium-N just accounted for 1.47%-3.75%.(4) The characteristics of greenhouse gas emissions in farmland from organic and conventional management. Organic management could improve the emission of greenhouse gases than conventional management to some extent, but there was no difference between each treatment. The effects for seasonal emission trend under organic, conventional and contrast were the same, and both of the greenhouse gases appeared emission peak after fertilization. CO2、CH4 and N2O fluxes under organic management were 5.46%,154.81% and 5.88% higher than under conventional management, respectively. The annual emission laws of CO2 reduced from May 2014 to March 2015 gradually, while CH4 presented "V" shape, the emissions in July were lowest, and N2O presented three peaks in June, September and November. CO2 was the main greenhouse in tea garden, the emissions of CH4 were generally low... |
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