The effect of liming on the quantity-intensity relationships of zinc fractions in soils
Literature was reviewed on zinc fractionation and factors affecting the availability of zinc to plants. An experiment was conducted to study the effect of liming on zinc fractions in soils. Liming decreased exchangeable zinc. However, no definite trend was observed in the other zinc fractions with increasing soil pH. An understanding of the distribution of zinc among various fractions in soils is important to understanding its soil chemistry. An experiment was further conducted to study the effect of liming and types of anion on the quantity-intensity relationships of zinc in soils. It was found that for all the soils, at the same level of added zinc, adsorption increased with increasing lime rates. Zinc adsorption isotherms with NO3- and C1- as counter ions have smoother curves than with SO42- and H2PO4-. The adsorption was highest with NO3- and lowest with H2PO4- as the background anion. Quantity and intensity factors influence the availability of nutrients in soils to plants. These factors describe what is referred to as the `labile pool'. Understanding of zinc labile pool is enhanced by radio isotope usage. Hence, an experiment was conducted to study the effect of liming on zinc labile pool as measured by the uptake of ryegrass utilizing the radioactive isotope of zinc. For both two harvests of perennial ryegrass there was a decrease in shoot zinc concentrtion and uptake with increasing lime rates. Higher zinc concentration was found in the soils with zinc-65 than without zinc-65. No definite trend was however observed in zinc labile pool with increasing lime rates. Several forms of zinc fertilizer are available for correcting zinc deficiency in soil. Variation in the ability of plants to absorb and utilize the different forms of zinc have been observed by many researchers. An experiment was conducted to study the effect of liming and types of complexing agent on the chemical composition of winter wheat grown on two soils of varying texture. The zinc forms differed significantly at the lime rate zero in relation to foliar zinc concentration. A decrease in shoot zinc concentration and uptake was observed with increasing lime rate. A similar trend was observed for one soil in relation to phosphorus concentration, except at the highest lime rate, where it remained fairly constant. There was however, an increase in shoot calcium concentration and uptake with increasing lime rate.