Impacts of soil depths on phosphorus leaching losses in manural loessial soil

Effects of soil depths on phosphorus leaching losses under the rotation system of winter wheat summer maize in manural loess soil were studied by using lysimeters with refilled soil. The results showed that the cumulative leachates and total phosphorus (TP) losses were decreased with the increase of phosphate fertilizer rates in the lysimeters when soil depth is less than 80 cm. The cumulative amounts of leachates and TP in the leachates were reduced with the increase of soil depth under the various fertilizer treatments. The decreased ratios of cumulative leachates were similar to those of total phosphorus in the leachates from the lysimeters those have a soil depth of 80 cm compared with 50 cm soil depth in all treatments. The argillic layer at the depth of from 77 to 155 cm in the soil significantly impedes the downward movement of soil water, thus the leaching losses of phosphorus. Phosphorus leaching was observed mainly in the form of dissolved phosphorus, and the proportion of total dissolved phosphorus to total phosphorus in the leachate was about 70%, while particulate phosphorus accounted for about 30% of the total leached P. The effective management of soil water and fertilizer P would be the most efficient approach to mitigate the downward movement of soil phosphorus in loessial region.