MSc

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.