Influence of soil pH on aluminum availability in the soil and aluminum in tea leaves

Soils and tea leaves from thirteen tea gardens located in east China were collected to investigate the effect of soil pH on the availability of aluminum (Al) and its uptake by tea plants. The soil samples were obtained from two horizons, i.e., 0-20 cm and 20-40 cm, with pH ranging from 4.05 to 7.11. Solubility of Al in soils, and hence its availability to the tea plant [Camellia sinensis (L.)], was estimated using extraction of soils with 0.02M CaCl2 and Al was determined by ICP-AES. Concentration of Al in tea leaves was similarly determined after acid digestion with concentrated nitric and perchloric acids. The concentration of Al in tea leaves could be predicted by 0.02M CaCl2 extractable Al in subsoil (r=0.79) other than that in topsoil (r=0.64). Extractable Al in soils and the uptake of Al by tea leaves both increased with decreasing soil pH. The relationships are both curvilinear with marked increase in extractability and uptake of Al when the soil pH falls below 5.0. It indicates that the speciation of Al in the soils changes at this pH value, and that the species of Al taken up by tea plants should be Al3+, which is the main form of Al in the soil pH below 5.0. It is concluded that soil pH was the major factor that controls the uptake of Al from soil into the tea plant.