Effect of soil organic matter on the contents of availableand water-extracted phosphorus

A total of 40 soil samples of 4 soil types were collected in cultivated farmlands in the outskirts of Luoyang and analyzed using conventional methods for the effects of soil organic matter content on the concentrations of available phosphorus, total phosphorus and water-extracted phosphorus. Based on soil organic matter content less/greater than 16.0 g·kg^-1, the soil samples were divided into two groups, and the relationships between available and total phosphorus, and water-extracted and available phosphorus in the two groups estimated. The results showed that the slope of linear correlation between available and total phosphorus was higher in soil sample group with >16.0 g·kg^-1 organic matter content than the group with <16.0 g·kg^-1 organic matter content. Also the slope of linear correlation between water-extracted and available phosphorus was lower in the >16.0 g·kg^-1 organic matter group than in the <16.0 g·kg^-1 organic matter group. This trend was shown in both the Olsen and Mehlich-3 extraction methods. The study showed that under low soil phosphorus, high content of soil organic matter meant less soil available phosphorus. This also resulted in high water-extracted phosphorus concentration. It in turn meant that in soils with high organic matter content and low phosphorus, phosphorus recycle was much faster. When soil phosphorus content increased, available phosphorus concentration increased more rapidly in soil samples with high soil organic matter. Meanwhile, water-extracted phosphorus increase was relatively slow. The study throw further light on the need and strategies of reducing leaching loss of phosphorus.