Effects of liming on dry biomass, lead concentration and accumulated amounts in roots and shoots of three tropical pasture grasses from lead contaminated acidic soils

Abstract

Liming the contaminated soil is the most widely used remediation treatment to reduce the bioavailability of heavy metals. The objective of this study was to evaluate the effect of liming on the change of dry matter and lead uptake by three tropical pasture grasses from lead contaminated acidic soil. Lime at five rates of 0, 1, 2, 3 and 4 g kg−1 soil was amended to the Neubauer's pots filled with 500 g Kunigami‐maji soils and then the limed soil was contaminated with 150 mg kg−1 lead after it was maintained for 1 week. Addition of lime increased soil pH significantly from 4.43 to 5.40. The root and shoot dry matter of all three tropical pasture grasses increased with the increasing doses of lime. An elevation of soil pH induced by liming resulted in a significant reduction of lead concentrations in both roots and shoots of all experimental grasses. The effectiveness of liming on lead concentration and accumulation varied with the pH values of limed soil and grass species. The results of this study imply that napiergrass was the most effective tropical pasture grass in reducing lead concentration and accumulation of roots and shoots as a consequence of liming, and could be used for lead stabilization in moderately lead contaminated acidic soil. The shoot lead concentration of napiergrass in limed soils was within the critical level of lead tolerable to feeding domestic animals, and may act as low level lead toxicity in fodder for grazing livestock. However, lime application or soil pH had a little influence on the lead accumulated amount in roots and shoots of atratum and signalgrass. The high amounts of lead accumulated in shoots of atratum and signalgrass were found to be useful for lead phytoextraction.