Effects Of Interaction Of Silicon-Calcium-Aluminum On The Adsorption Capacity And Active Aluminum In Tea Garden Soil

Aluminum (Al) is one of elements impacting the human health. Tea plant is known to be a typical aluminum accumulator, which contains high level of Al in the tea leaves. Generally, the uptake of Al from soil into tea leaves is involved mainly in soil properties as well as forms of Al in soils. Moreover, the water-soluble and exchangeable Al are considered to be the most active forms of Al, which can be taken up by tea plant directly. The adsorption characteristics of Al affect the Al activity in tea garden soil to some extent, furthermore, calcium (Ca) and silicon (Si) can influence the Al activity through the competition adsorption between Ca and Al or Si and Al, as well as the formation of compound or chelate between Si and Al. As a result, the uptake of Al from soil into tea leaves will be connected closely with the interaction among Ca, Si and Al in tea garden soil. Consequently, there will be of theoretical and practical significance to systematically study the effects of the interaction among Ca-Si-Al on the adsorption capacity and activity of soil Al for decreasing Al content in tea leaf by adjusting the soil condition and further protecting the human health from the impaction of Al. The effects of the interaction among Ca-Si-Al on the adsorption capacity and activity of soil Al with or without the extraneous source organic matter were studied systematically by sampling tea garden soil and laboratory simulation in the paper.Results from the Adsorption dynamics and thermodynamics of Al in tea garden soil showed that the time of adsorption equilibrium was at 35 min or so under the interaction of Si-Al and 60-80min under the interaction of Si-Ca-Al. The adsorption amounts of aluminum in the tea garden soil increased continuously with increasing the beginning concentration of aluminum within the test concentration under the interaction of Si-Al or Si-Ca-Al. However, the adsorption amounts of aluminum was higher slightly for high ratio of Si to Al than that for low ratio Si to Al under the same Ca amount and for high ratio of Ca to Al than that for low ratio Ca to Al under the same Si amount. This indicated that Ca and Si can promote the adsorptive capacity of Al in tea garden soil. The adsorbing rate of aluminum increased obviously and the equilibrium time was at 20 min for different ratio of Si to Al, and there was no variation in the adsorption amount for the ratio of 2Si/Al and Si/Al but distinct decreasing for the ratio of Si/2Al under existing extraneous source of organic matter. The adsorption amount of Al in the tea garden soil increased with increasing the content of organic matter and the ratio of Si to Al. The desorption rate of Al in tea garden soil decreased with the increase of adsorption amount of Al and the ration of Ca to Al or Si to Al, nevertheless, the extraneous source of organic matte could promote the desorption rate of Al in tea garden soil.Results from the effects of interaction of Si-Ca-Al on the activity of Al in tea garden soil with or without extraneous source of organic matter showed that:the content of active Al changed little for the lower adsorption amount of Al under different ratio of Ca to Al and decreased for the higher adsorption amount of Al Ca to Al, but the content of the exchangeable Al was higher than by far that of water soluble Al under the same amount of adsorption Al and ratio of Ca to Al; the content of exchangeable Al increased with increasing the amount of adsorption Al under different ratio of Si to Al, and the content of water soluble Al decreased under the ratio of Si/Al and Si/Al and increased under the ratio of 2Si/Al with increasing the amount of adsorption Al; the activity of Al decreased with the ratio order of 2Si/Al, Si/2A1 and Si/Al; the content decreased for the water soluble and increased for the exchangeable Al under lower amount of extraneous source of organic matter (5% and 10%) with increasing the ratio of Si to Al, there was, however, not obvious change in the content of water soluble and exchangeable Al under higher amount of extraneous source of organic matter (15%) with increasing the ratio of Si to Al. In conclusion, the existing of Si made the active Al of tea garden soil decrease under the lower content of extraneous source of organic matter.