Effects of acidification and CaCO3 application on various forms of manganese in soils

Studies were conducted to assess the transformation of various Mn forms in 3 of acidified soils in the Central China before and after application of CaCO3 contrasted to a kind of calcareous alluvial soil The results showed that soil acidity decreased in the acidified red soil, brown red soil and yellow cinnamon soil by applying of CaCO3 With decrease of pH, the content of exchangeable Mn (EXC Mn) increased by 42%, 49% and 39% in the above soils, respectively, while that of easily reducible Mn (ERO Mn) decreased on the contrary The contents of calcium carbonate bound Mn (CARB Mn), organic matter bound Mn (OM Mn) and reducible Mn (RO Mn) only changed slightly, and residual Mn (Res Mn) altered more lightly In the calcareous alluvial soil, the content of EXC Mn was rather small, ERO Mn was main part of active Mn, and CaCO3 application had little influence upon other forms of Mn Due to no correlation between EXC Mn and CARB Mn, they were independent to each other, i e , they were different bound forms in soil surface EXC Mn was a kind of exchangeable cation which was adsorbed by negative charge of soil CARB Mn was occluded by easily dissolved oxides in acidic soil or was adsorbed by carbonate precipitates in calcareous alluvial soil It was a kind of intermediate between EXC Mn and ERO Mn and could easily transform into ERO Mn After applying CaCO3 to acidified soil, in which EXC Mn would be changed into CARB Mn, even into ERO Mn, that was the effect of applying CaCO3 to overcome toxicity of EXC Mn in growth of crops