Nature of acidity in upland and rice fallows in relation to response of pulse crop to liming

Abstract

Soils over vast areas of uplands and rice lands in Kerala are acidic in nature. High concentrations of Al and Mn often limit the productivity of pulses when grown in these areas. The present investigation was aimed at detecting the toxic factors causing acidity and locating suitable varieties of cowpea and blackgram suited to these soil situations. It was further programmed to find out the optimum levels of lime that would be required to arrive at a low input management programme for pulses. For this purpose a large number of soil samples were analysed. Several pulse varieties were screened in respect of their tolerance and a pot culture study was conducted to assess their productivity, the results of which are summarised and appropriate conclusions drawn. The collected soils were acidic in nature, the factors causing toxicity being high concentration of Al and Mn. The soils require large amount of lime as amendment. Cation exchange capacity of these soils is very low and to some extent contributed by Al and Mn. Screening experiments were conducted to select varieties which are tolerant to Al and Mn toxicity. As a result S-488, a cowpea variety and Velloor, a blackgram variety were selected as tolerant ones. Comparative assessment of the yielding ability of the selected varieties, with the recommended varieties New Era (cowpea) and T9 (Blackgram) revealed that they could yield as much as or even better than the recommended varieties. The recommended varieties require high doses of lime for a substantial yield whereas the selected varieties could give economic yield with practically no liming. The observations on number of pods, grain yield, haulm yield and number of nodules revealed that the two selected varieties could excel the others in these aspects Uptake studies indicated that the increased yield in the case of the selected varieties is mainly due to the enhanced uptake and fixation of N and uptake of P and K. From the results of the study, it was concluded that the cowpea variety S-488 and the blackgram variety Velloor can be cultivated successfully under acid soil conditions. They possess the ability to give economic yields with little or no liming. These results have to be tested in farmers 'fields to evolve a low input management strategy for pulse cultivation in garden lands as a vegetable in kharif season and in the rice fallows in summer season.