Evaluation of the fertilizer value of some indigenous rock phosphates and basic slag of India

Summary Field and pot culture experiments were conducted in terai acid soil (Haplaquoll) to evaluate the fertilizer value of one basic slag and two rock phosphates, such as Purulia rock phosphate (Igneous) and Mussoorie rock phosphate (sedimentary). In the field experiments two crop sequences were followed: (i) Rice — wheat — greengram (ii) Greengram — rice — wheat. In terms of crop yield and P uptake Purulia rock phosphate did not show any significant effect, except in case of greengram grown as the third crop after its application. Mussoorie rock phosphate increased the yield and P uptake through its direct and residual effect in all the crops, except in rice. Irrespective of crop species and crop sequences basic slag showed considerable direct and residual effect in increasing the crop yield and P uptake. Its effect was at par with that of superphosphate. By total yield increase of three consecutive crops due to added P the efficiencies of the fertilizers were graded as basic slag > superphosphate = Mussoorie rock phosphate > Purulia rock phosphate for rice — wheat — greengram rotation and superphosphate > basic slag > Mussoorie rock phosphate > Purulia rock phosphate for greengram — rice —wheat rotation. Composting improved the efficiency of all the insoluble phosphatic fertilizers.