Characteristics of phosphorus leaching and its impact on groundwater in purple paddy soil

In this paper, the dynamic loss of phosphorus by leaching was studied by collecting seepage in paddy season from different soil profiles using an in situ soil drainage lysimeter, and analyzing the relationship between soil Olsen-P and phosphorus loss. The results showed that phosphorus seepage decreased over time, but the amount leached was high and variable at the earlier stages. Concentration of leached phosphorus was the highest in all soil layers 5 d after fertilizing, and remarkably decreased by 60 d after fertilizing. It reached coincidently at all different soil profiles with all treatments. Phosphorus leaching was affected by the phosphorus fertilizer and soil properties. As expected, the amount of P leached increased with the amount of fertilizer applied. The amount of P leached decreased in the order neutral soil>calcium soil>acid soil at different profiles in the three kinds of purple soil. The average leaching losses of phosphorus after treatment with phosphorus fertilizer were in the range of 0.13-0.142 mgL-1, 0.097-0.131 mgL-1 and O.083-0.109 mgL-1in neutral, calcium and acid soil at 40 cm depth, which were33.1%-38.7%, 24.7%-44.3% and 34.9%-50.4% higher than with no fertilization, respectively. Similar results were also obtained at 60 cm and 100 cm depths. Moreover, there was an exponential relationship between Olsen-P and phosphorus leaching in the three kinds of purple soil. Phosphorus concentration of seepage water decreased with soil depth. In the initial stage of paddy growth, phosphorus moved downward the most and the leaching amount was the highest. In all three purple soils, the seepage of phosphorus could bring potentially unfavorable influence on underground water 60 d after fertilizing. Phosphorus loss was low over the whole paddy season, however, with the highest value=0.262 kghm-2.