A study of the effect of soil pH on chemical species of cadmium by simulated experiments.

The effect of soil pH on various chemical species of cadmium in paddy soil, purple soil and yellow soil was studied by a series of simulated experiments. The results show that 1 under alkali condition the percentage of dissolvable Cd is less than 3% but it increases significantly with a decrease in pH value when pH value is less than 6.5, and it reaches 48.39% when the pH value is 4.57 in paddy soil; 2 the percentage of exchangeable Cd decreases rapidly with the increase of pH value under basic condition but displays an increasing trend under acid condition; 3 the percentages of Cd bound to carbonates and bound to Fe-Mn oxides increase with the increase of pH; and (4) the percentage of Cd bound to organic matters mildly increases with the increase of the pH. From this study, we suggest that an efficient way to reduce the harmful effects of Cd to the ecosystem is to hold the pH value of soils at greater than 6.5 and/or to fertilize soil by organic manure.