Distribution Of Phosphorus And Environmental Risk Of Soil Phosphorus Loss In Quanzhou City

As a typical area of the interaction between human beings and environment, city is also the most drastic area affected by human activities. At present, quantity of raw and agricultural soils has been damaged by the expending of urbanization. The evolvement of urban soil's quality and the ecological and environmental impact of this evolvement are the significant parts of the relations between human beings and environment, and they are also the basement for the sustain development of city. Quanzhou is a city with many lakes, which are suffering rather serious eutrophication. Phosphorus, as a key factor of the formation of water eutrophication, is certainly worthy of more attention. However, there are few studies on soil phosphorus accumulation and loss potential. The changing character of soil phosphorus in the system of different land utilization of city soil is a significant problem concerned by the managers of urban soil and environment. In this study, the urban soil of Quanzhou city was used investigated to study the distribution and the loss risk of soil phosphorus under different land utilization. The main results were shown as follows:(1) The content of total P in urban topsoil of Quanzhou was high with considerable variation. the content of speciation phosphorus presented an order of Fe/Al-P > Re-P > Org-P > Ca-P > Exch-P. The contents of TP, various speciation P and water-dissolvable P were all higher than those in other functional zones due to the higher intensity of human activities and the larger population in the commercial zone. The average phosphorus activation coefficient(PAC)in all studied functional zones was above 2.0%, and the PAC of agricultural zones reached 4.579%, indicating that attention should be paid to the rational application of fertilizer to avoid phosphate leaching and to prevent the occurrence of face source pollution in the agricultural zones.(2) The content of available P in dryland soil was higher on the surface than other layers, and presented a decreasing trend with soil depth, while available phosphorus increased gradually with depth in the paddy soil, which indicated that the loss of available phosphorus was obvious in the traditional irrigation and fertilization. The distribution of speciation phosphorous in the profiles of dryland and paddy field showed no regularity. And the variability of phosphorus in the same and different sections of the dryland is stronger than that in the paddy field. This is due to the effect of human activities on the dryland soil, and the soil profile was often affected by human beings. According to the correlation analysis, a conclusion could be made that Exch-P was the most direct source of available phosphorus in the soils of dryland and paddy land. (3)The adsorption and desorption character of soil phosphorus under different land utilization was analyzed. The results showed that Langmuir isotherm equation could describe the soil P sorption characteristics well. The adsorption capacity of soil P in rotation land and dryland was higher than that in grassland and forestland. And the loss risk is in the order of rotation land > grassland > forestland > dryland. The recommended P application rate was in accordance with the soil P adsorption constant and the maximum buffering capacity in the sequence of dryland > rotation land > forestland > grassland. The soil P desorption rate of rotation land and grassland was higher than that of dryland and forestland, and the soil P buffering capacity follows the order of dryland > forestland > rotation land > grassland. The analysis of principal component revealed that the mean P desorption rate, easily desorbable P, P sorption index and equilibrium P concentration could reflect the loss potential of soil P best, and could be used as the main indices to assess the loss potential of soil P.(4) The correlation was analysed for 25 topsoil samples (0 - 20 cm) collected from Quanzhou suburb. The results showed that the correlation was significant among soil Olsen-P, TP, DPS and CaCl2-P. The Olsen-P couId be used as an evaluating indicator of the leaching risk of soil P. The critical value of leaching P from soil was 40 mg/kg, and about 36% soil samples'Olsen-P exceeded that critical value. The critical value of leaching P which could cause water eutrophication was 60 mg/kg.