Soil P desorption in different land use types in Dianchi Lake Watershed

Non-point P pollution is the main element of eutrophication of Dianchi Lake. Study of dissolved soil P is critical because of its ease of utilization by aquatic plants especially when flushed into Lakes. 17 soil sampling sites of 5 land use types were selected, and total P, available P, total dissolved P and dissolved phosphate contents of sampled soils were determined. P desorption experiment of sampled soils was conducted too. The aim of the study was to learn the desorption characteristics of P in soils of different land use types in Dianchi Lake Watershed. Based on the results, the orders of soil total P and available P in different land use types were abandoned lakeside greenhouse > greenhouse > flat-land > slope-land > woodland with the contents ranges of 0.124~2.935 g·kg^-1 for total P and 0.311~96.238 mg·kg^-1 for available P. The total dissolved P content range was 0.66~9.52 mg·kg^-1 and its order for differ-ent land use types was abandoned lakeside greenhouse > greenhouse > slope-land > flat-land > woodland. Soil dissolved phosphate content under different land use types was lower. Soil total dissolved P was linearly positively correlated with soil total P. Soil dis-solved phosphate was also linearly positively correlated with soil total dissolved P. Dissolved phosphate was 20%~95% of total dis-solved P. These trends implied that dissolved phosphate was important component of total dissolved P, and the degree of soil dis-solved P was determined by the amount of soil total phosphorus. Also the higher the rate of P fertilization in the region, the more difficult was the control of eutrophication in Dianchi Lake. The study showed that dissolution of soil total P reached equilibrium in about 0.5~1 hours of application. This implied that there was sufficient time for P to attain dissolution equilibrium as it moved down in the lake through groundwater flow or surface runoff.