Key Laboratory of Agro-Ecological Processes in Subtropical Region,Institute of Subtropical Agriculture,Chinese Academy of Science,Changsha 410125,China%College of Environment and Municipal Engineering,Xi′ an University of Architecture and Technology,Xi′ an 710055,China

paddy soil in subtropics%nitrogen and phosphorus leaching%dynamic characteristics%suction cup sampling method%waterlogged condition during fallow season

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.