Selenium Contents and Forms in Soils at Tea Plantations of Different Soil Types in Northern Fujian

Distribution of available selenium (Se) in soils at tea plantations of different soil types in northern Fujian province was determined to analyze the factors that contributed to the variations. Thirty-five specimens of surface soil at the depth of 0-20 cm from tea plantations of yellow soil, red earth, moisture sandy soil, and purple soil types in the region were collected. The chemical analysis showed that the total Se contents of the soils ranged from 0.22 mg·kg^-1 to 1.07 mg·kg^-1 with an average of 0.59 mg·kg^-1. A great majority of the area soil, i.e., 82.86%, belonged to the Se-rich classification. The availability of Se, however, was low, ranging from 1.10% to 31.64% with a mean of 8.34%. Among the different soil types, the yellow soil was the highest in contents of total and various forms of Se, while the sandy soil lowest but most available for plant utilization. The contents of various forms of Se were lower in the order of organic matter-bound Se ＞ residual Se ＞ exchangeable and carbonate-bound Se ＞ iron and manganese oxides-bound Se ＞ soluble Se. The chemical form was critically affected by the organic matters, pH, and nitrogen in the soil with significant positive correlations between available phosphate and total Se and between organic matter-bound Se and residual Se. On the other hand, there were no significant correlations between iron or manganese oxides-bound Se and soil physiochemical properties. In general, the soil in the region was rich in Se for tea cultivation, but the relatively low availability of the element deterred the potential benefit. Hence, improving Se bioavailability at the tea plantations would be a most desired task facing the scientists and industry.