| Nitrogen（N） and phosphorus（P） leaching in soil is regarded as one of the important aspects of agricultural nonpoint source pollution. The characteristics of N and P leaching from a double rice-cropped paddy soil in subtropics with two fertilization treatments（Fert：195 kgN·hm-2 season-1 and 69 kgP·hm-2 season-1, and CK：no fertilizers）were studied using a suction cup sampling method. The field observations were conducted at four soil depths：15 cm, 30 cm, 60 cm, and 90 cm from soil surface and from April 2010 to November 2011. Our results showed that compared with CK the Fert treatment significantly enhanced the leaching of N and P in paddy soil, in particular during the rice growing season. The leached N was observed significantly different（P<0.05） in N forms at different observation times, i.e. ammonium N dominated during the rice growing season under water-logged condition（April-middle October） and contrarily nitrate N prevailed during the fallow season under drained condition（late October-March）. This was expected to be attributed to the alteration of soil aeration. The P leaching risk in the fallow season（October-December） under drained condition was significantly greater than other periods. Therefore, the fallow season was probably the key P leaching period in the paddy soil in this area. We speculated that controlling N and P accumulation in soil and strengthening water management during the fallow season could be the effective approaches to reduce N and P leaching risk of paddy soil. Besides, it was also found that compared with the 0.01 mol·L-1 CaCl2 and Olsen（0.5 mol·L-1 NaHCO3） extraction methods, the Bray-1（0.03 mol·L-1 NH4F + 0.025 mol·L-1 HCl） method performed the best to determine the P leaching risk of paddy soils in this study area. |
