Characterisation of acidity and its management in rubber growing soils

Abstract

Soils under rubber cultivation are acidic in reaction. Most of the rubber plantations in the traditional belt of rubber cultivation in India are in the second or third planting cycle. Continuous cultivation of rubber was reported to reduce the soil pH because of removal of basic cations and increase in Al content. The present investigation was carried out with the following studies viz., i) collection of soil samples representing the major soil series and characterization of the nature of soil acidity ii) estimation of the lime requirement of these soils iii) incubation experiment to study the changes in nutrient availability through liming (iv) field experiment to study the effect of liming on growth of rubber seedlings in the nursery (v) experiment in the glass house with poly bags to understand the translocation of Ca in different plant parts upon liming and (vi) two nursery experiments to compare the direct and residual effect of different liming materials on growth of rubber seedlings in the nursery. Characterisation of acidity in the major soil series of the traditional tract revealed that the dominance of different forms of acidities were total potential acidity.gtpH-dependent aciditygt exchangeable acidity. The important factors responsible for acidity in these soils were different forms of Al, organic carbon and clay. High Al saturation of the exchange complex was recorded due to the high concentration of different forms Al viz., soluble, exchangeable, extractable and non exchangeable Al. Subsoil acidity was observed in these soils. Soluble Al content was found to increase with increase in Al saturation percent. The inverse relation between newlineexchangeable Al and exchangeable Ca points to the deleterious effect of soil acidity on Ca availability. Aluminium toxicity coupled with Ca deficiency reduces the root penetration into the subsoil leading to lower utilization of mineral nutrients and water from subsoilHence, further studies will be needed in areas where high concentration of Al in soil solution.