Lei Wang;Clayton R. Butterly;Qiuhui Chen;Zhibo Mu;Xia Wang;Yunguan Xi;Jibing Zhang;Xiang Xia

State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China);Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing 210042 (China;Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing 210042 (China);AgriBio, Centre for Agri-Bioscience, La Trobe University, Melbourne VIC 3086 (Australia);Suzhou Xiangcheng District Environmental Monitoring Station, Suzhou 215100 (China)

subsoil acidity;alkalinity;cm;05;subsoil;decrease

Strongly acidic soils (pH < 5.0) are detrimental to tea (Camellia sinensis) production and quality. Little information exists on the ability of surface amendments to ameliorate subsoil acidity in the tea garden soils. A 120-d glasshouse column leaching experiment was conducted using commonly available soil ameliorants. Alkaline slag (AS) and organic residues, pig manure (PM) and rapeseed cake (RC) differing in ash alkalinity and C/N ratio were incorporated alone and in combination into the surface (0-15 cm) of soil columns (10 cm internal diameter x 50 cm long) packed with soil from the acidic soil layer (15-30 cm) of an Ultisol (initial pH = 4.4). During the 120-d experiment, the soil columns were watered (about 127 mm over 9 applications) according to the long-term mean annual rainfall (1 143 mm) and the leachates were collected and analyzed. At the end of the experiment, soil columns were partitioned into various depths and the chemical properties of soil were measured. The PM with a higher C/N ratio increased subsoil pH, whereas the RC with a lower C/N ratio decreased subsoil pH. However, combined amendments had a greater ability to reduce subsoil acidity than either of the amendments alone. The increases in pH of the subsoil were mainly ascribed to decreased base cation concentrations and the decomposition of organic anions present in dissolved organic carbon (DOC) and immobilization of nitrate that had been leached down from the amended layer. A significant (P < 0.05) correlation between alkalinity production (reduced exchangeable acidity N-cycle alkalinity) and alkalinity balance (net alkalinity production N-cycle alkalinity) was observed at the end of the experiment. Additionally, combined amendments significantly increased (P < 0.05) subsoil cation concentrations and decreased subsoil Al saturation (P < 0.05). Combined applications of AS with organic amendments to surface soils are effective in reducing subsoil acidity in high-rainfall areas. Further investigations under field conditions and over longer timeframes are needed to fully understand their practical effectiveness in ameliorating acidity of deeper soil layers under naturally occurring leaching regimes. Key Words: Al saturation, leaching, nitrate, organic amendments, organic anions, pH, soil acidity, soil alkalinity