Aluminum sorption by plants as influenced by calcium and potassium

Abstract

The uptake of K, Ca and Al by plants was studied in three steps: first, adsorption; second, absorption by excised roots; third, uptake by the intact plants. Cation exchange capacities of the plant roots were as follows: Ananas comosa (pineapple) 7.0, Saccharum officinarum (sugarcane) 9.5 Zea mays (corn) 13.6, and Desmodium canum (kaimi clover) 20.0 m. e. per 100 g. dry roots. Cation adsorption on root surface was observed to be a function of plant species, cation involved and cation concentrations in equilibrating media. The adsorption of Ca and AI on roots of all species increased with increasing cation exchange capacities. However, the adsorption of K was preferential on corn roots. The amount of cations adsorbed increased with their increasing concentrations in equilibrating media. The effects of one cation upon the adsorption of another cation A were reciprocal. At equivalent cation concentration in the saturating solution, cation adsorption by all roots decreased with increasing cation valency. The Al adsorption was influenced by the complementary cation, being higher with Ca than with K. In pineapple and kaimi clover roots, aluminum depressed the sorption of Ca, but stimulated that of K at low concentration. A highly significant correlation was observed between adsorption and absorption of individual cations within each plant species. It is suggested that absorption of a cation is related to its adsorption and amount of appropriate metabolically produced carrier by roots. Pot experiment was conducted to investigate the effect of 5, 20 or 60 percent Ca and 1 or 10 percent K saturations on the dry matter yield and mineral composition of corn and kaimi clover. When the soil pH was allowed to vary from 5.2 to 7.0 depending upon K and Ca applications as hydroxides, K added in excess of 1 percent saturation decreased the yield of both plant species at all levels of Ca. At pH 4.9, corn yield increased by increasing K saturation at 20 or more percentage Ca, but markedly depressed at 5 percent Ca saturation. However, regardless of Ca levels, the yield of kaimi clover decreased with higher K saturation. The amount of cations distribution from the root to the top was shown to depend considerably on the individual ions. More than 80 percent K and Ca absorbed were in the' plant top, but most of Al remained in the roots. Apparently plants differ in their capacity to transfer Al into their aerial portions. The net translocation of Al in kaimi clover was twice than that in corn.