Exchangeable aluminium as an index of the lime requirement of the laterite soils of Kerala

Abstract

An investigation was taken up to assess the lime requirement in terms of exchangeable aluminium, to correlate pH and lime requirement values with exchangeable aluminium content of the soil and to study the effect of liming on crop performance with special reference of exchangeable aluminium content of the soil. The study was carried out at College of Horticulture, Kerala Agricultural University, Vellanikkara, Thrissur during the period from 1993-95. The investigation consisted of three phases. A laboratory study with fifty surface soil samples from the rice growing tracts representing the laterite zone of Kerala viz., Malappuram, Palakkad and Thrissur districts revealed considerable amount of reserve acidity because of the positive difference between pH(H2O) and pH(KC1). pH showed significant positive correlation with base saturation while it showed negative correlation with the acidity contributing factors. The exchangeable aluminium content of the soils ranged from 0.25 to 2.54 cmol( +) kg -1. The soils in the pH range of 4.8 to 5.8 were predominant with exchangeable aluminium. Exchangeable aluminium obtained a higher r value of 0.897** with exchange acidity than exchangeable hydrogen (r = 0.57**). Moreover exchangeable aluminium contributed 69 to 86 per cent towards the exchangeable acidity. This high contribution should be taken into account in timing and nutrient management of the soils.

The pH dependent acidity contribution towards total acidity was 23-63 per cent, 34-76 per cent and 20-76 per cent respectively for Malappuram, Palakkad and Thrissur soils. Among the cations studied exchangeable calcium dominated in all soils followed by K, Mg and Na. Maximum base saturation value and organic carbon contents were observed in Malappuram soils. Lime requirement based on exchangeable aluminium recorded the lowest quantity of CaCO3 when compared to LR's based on Shoemaker et al. and total acidity. The soils had higher concentra- tions of total iron and aluminium contents. A pot culture experiment was conducted to study the effect of graded levels of lime application using the rice variety Triveni in three soils. Lime application increased the pH, exchangeable calcium, magnesium and sodium, available phosphorus, CEC, ECEC and base saturation of the soils while decreased exchangeable aluminium, hydrogen and potassium content of the soils. Different forms of acidities were maximum at the pre-planting stage but decreased as the crop matured. Lime application significantly increased the straw and yield characters of rice over control in all the three soils. Maximum yield was obtained with calcium at the rate of 0.5 and 1.0 times of exchangeable aluminium equivalent in soil (S1) having low exchangeable aluminium and those having medium (S2) and high (S3) contents respectively. The per cent composition of N, P, Ca and Mg increased significantly in the straw while that of iron and aluminium decreased with lime application. N, P, K and Ca content were observed maximum at tillering stage. The N, K, Ca and

Mg content in the grain increased while that of P, Fe and Al decreased with graded levels of lime application. The total uptake of N, P, K, Ca and Mg by both straw and grain was found to increase while that of Fe and Al were found to decrease with increased levels of lime. Incubation study exhibited similar results and trend as in the pot culture experiment. The soil characters such as pH, available phosphorus, exchangeable Ca, Mg, Na, CEC, ECEC and base saturation were increased whereas exchangeable aluminium, iron, hydrogen and potassium, and different forms of acidities were decreased by the application of graded levels of lime. The soils kept under the submerged conditions exhibited good results than those kept at field capacity level. The lime requirement of soils calculated based on various methods revealed that the LR based on exchangeable aluminium content of soils required very less quantity of CaCO3. The exchangeable aluminium contributed 69 to 86 per cent towards exchangeable acidity. This high contribution of exchangeable aluminium should be taken into account in liming and nutrient management of the laterite soils. If we adopt this method for lime requirement determination it will be more efficient and economical. Thus the results of the present study point out the advantages in adopting the exchangeable aluminium as an index of the lime requirement of the laterite soils of Kerala.