Methods to increase the efficiency of rajphos (Jamarkhotra Rockphosphate) in the black soils of Palakkad district for rice

Abstract

There has been considerable interest in studying the efficiency of rockphosphate for direct application to the soil in the rice farming situations of Kerala, particularly tapping the iron - to - magnet type of relationship between rockphosphate and acid soils. However no work has been done in the neutral to alkaline soils of Kerala located in the Chittoor Taluk of Palakkad District to utilize the potential of rockphosphate. These soils are inherently poor In phosphorus and the situation 1S furthur complicated by the high P fixation capacity. Problems of fixation of soluble P can be alleviated to some extent by the use of less soluble forms like rockphosphate in conjunction with acid forming amendments like iron pyrites. sulphuric acid and P solubilising micro organisms. A study was undertaken to investigate the effect of direct application of rockphosphate in combination with amendments for rice in the Department of Soil Science and Agricultural Chemistry at the College of Agriculture, Vellayani. There were two experiments, an incubation study to investigate the relative efficacy of various amendments in releasing soluble P from rockphosphate and a pot culture experiment to study the comparative efficiency of rock phosphate with amendments.

Incubation experiment shows an Increase In P fractions like saloid-P, occluded-P, reductant-P, Fe-P, AI-P and Ca-P upto 45 days which decreased subsequently with the advancement of time. The values stabilized towards the last observation at around 90 days of incubation which was higher than the initial starting values. Rock phosphate acidulated with sulphuric acid and amended with pyrite at all levels of P addition increased P fractions. Inoculation of phosphobacterin was also effective though the release of P was slightly lower than treatment with chemical amendments. In the pot culture experiment growth and yield character of crop were significantly influenced by treatments receiving rockphosphate amended with direct acidulation and pyrite application at all levels. Rajphos @ 45 kg ha' with 50 per cent acidulation was found to be on par with the treatment receiving Rajphos @ 30 kg ha" with 50 per cent acidulation. Rajphos treated with acid perform equally well as SSP and the results were comparable. The grain and straw yield and uptake of pi ant nutrients were significantly superior for treatment consisting of acidulated rockphosphate. Chemical amendment like iron pyrite and microbial inoculation with phosphobacterin was also found to be efficient but the effect was not significant statistically.