Risk assessment on soil environment quality and losses of nitrogen and phosphorus for the gravel soils under different farming practices in the watershed of Lake Fuxian

Abstract

On August 2006, grave soils from organic and conventional farming were sampled within the watershed of Fuxian Lake in Yunnan Province. Soil granule composition, heavy metal contents and nutrition accumulation in the soil profile were determined. Nitrogen and phosphorus losses from the soils were assessed by the in-door rainfall simulation. The results were as below: 1) both organic and conventional farming practices significantly lower the soil sand content on the 0-20 cm soil profile; 2) all soil heavy metal contents met the Class A standard of National Environment Quality Standard for Soils (GB/15618-1995) except Cd which only met Class B standard; 3) soil total nitrogen and organic matter accumulated in the 0-20 cm soil profile, and showed no significant differences between organic and conventional farming practices. The accumulation of soil total phosphorus, NO3-N and water dissolved phosphorus (WSP) under the organic farming practice is significantly higher than those under conventional farming practice; and 4) under the condition of 780 mm rainfall simulation, the risk of nitrogen and phosphorus losses from the organic farming soil is higher than that from the conventional farming. Total amount of nitrogen and phosphorus losses from the organic fanning soil were 1.9 and 19.8 times higher than those from the conventional farming soil, respectively.