Winter runoff losses of phosphorus from paddy soils in the Taihu Lake Region of South China q Huanchao Zhang a , Zhihong Cao a, * , Gaiping Wang b , Hongai Zhang b , M.H. Wong c a The Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China b College of Forest Resources and Environment, Nanjing Forestry University, Nanjing, China c Hong Kong Baptist University, Hong Kong, China Abstract A winter wheat field plot experiment was conducted on two types of paddy soils, from November, 2000 to June, 2001 to assess P losses to its surrounding watercourses by runoff in the Taihu Lake Region. Commercial NPK compound fertilizer and single superphosphate fertilizer were applied to furnish 0, 20, 80, and 160 kg P ha 1 . The experiments consisted of six replicates of each treatment in Changshu site and four replicates in Anzhen site, with a plot size of 5  6 m 2 in a randomized block design. Results revealed that the average concentration of dissolved P (DP), particulate P (PP), and total P (TP) in runoff water during the winter season was 0.13, 0.90 and 1.04 mg P l 1 respectively, from P20 plots in Anzhen site. While it was 0.67, 1.08 and 1.75 mg P l 1 respectively, from P20 plots in Changshu site. The seasonal TP load (mass loss) from P20 plot ranged from a low of 290.88 g Pha 1 season 1 to a high of 483.54 gPha 1 season 1 ,withameanof382.29gPha 1 season 1 in Anzhen, but from 444.92 to 752.21 gPha 1 season 1 , with ameanof539.13gPha 1 season 1 in Changshu. Both in Anzhen and Changshu PP represented a major portion of the TP lost in runoff, the average PP/TP was about more than 80% in P0 and P20 plot, but it was decreased with the increase of P rate. The average seasonal P loads (DP, PP, and TP) in Changshu were greater than in Anzhen although runoff volume in Anzhen (45 mm season 1 ) was more than in Changshu (36 mm season 1 ). This was probably asso- ciated with the differences of soil physical and chemical properties between the two sites. Phosphate fertilizer rate significantly affected P concentrations and P loads by runoff. Both the mean concentrations and the average seasonal P loads from the P80 plots were lower than from the P160 plots, but obviously higher than from the P20 and P0 plots. There was no significant difference found between the P20 plots and the P0 plots both in Anzhen and Changshu sites. It indicated that P loads by runoff would be greatly increased in 5–10 years due to the accumulation of soil P if 20 kgPha 1 applied each wheat season in this area. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Phosphorus loss; Runoff; Eutrophication; Winter time; Taihu Lake 1. Introduction Phosphorus is one of the essential nutrients for plant growth and its input has long been recognized as nec- essary to maintain profitable crop production. High phosphate fertilizer inputs to agro-ecosystems in the intensive crop areas have been occurred for several de- cades. This has resulted in significant P enrichment in soil profiles (Sharpley et al., 1993; Simard et al., 1995). It Chemosphere 52 (2003) 1461–1466 www.elsevier.com/locate/chemosphere q Project supported by the National Natural Science Foun- dation of China (No. 40171056) and by the National Key Basic Research Plain Foundation (NKBRPF) of China (No. G1999011806). * Corresponding author. Tel.: +86-25-7712-572; fax: +86-25- 3353-590. E-mail address: zhcao@issas.ac.cn (Z. Cao). 0045-6535/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0045-6535(03)00483-1