Saturday, 15 July 2006

Use of Indigenous Indian Rock Phosphates as Cheap Source of P to Increase Rice Production.

C.A Srinivasamurthy, Sunil Kumar, M.V. Ravi, S. Bhaskar, and R. Siddaramappa. Univ of Agricultural Sciences, Gandhi Krishi Vignana Kendra, Bangalore, 560 065, India

The main problem of Indian rice growers has been the supply of phosphorus economically due to steep rise in the prizes of imported raw materials required for the manufacture of water-soluble P fertilizers. The only alternative to this problem is utilization of indigenous phosphate rocks in low pH rice soils and evolving suitable techniques to increase the agronomic efficiency of these water insoluble rock phosphates. A pot experiment was conducted to find out the effect of time of application of P sources (water soluble and insoluble forms) on P transformation in soils and its availability to rice seedlings in four different low pH soils of Karnataka. Application of both water-soluble and water of insoluble P sources 7 days before transplanting produced highest dry matter yield of rice in all the soils compared to their application on the day of transplanting. Among the rock phosphates Mossoorie Rock Phosphate (MRP) resulted in higher dry matter yield than Udaipur Rock Phosphate (URP) in all the four soils but it was inferior to single super phosphate. The results indicate that in acid soils, rock phosphate a cheap source of P can be used as efficiently as single super phosphate by applying them to moist soil at the time of land preparation itself. Application of P (both water soluble and insoluble forms) significantly increased the available P content and Fe-P, Al-P and Ca-P fractions of soil indicating the ready transformation of applied P in these soils. A field experiment was conducted to study the effect of MRP, SSP and their mixture in 1:1 ratio with and without adjuncts like green leaf manure (glyricidia maculata) and P solubilizing fungi (Aspergillus awamorii) on rice (Cv. IET 7191) in an acid soil in the Westernghat region of Karnataka. Highest grain yield of rice was recorded when SSP was applied along with green leaf manure. Among the adjuncts, green leaf manure had better effect on rice yield than P solubilizing fungi when the adjuncts were added along with rock phosphate. Application of rock phosphate along with green leaf manure and P solubilizing fungi gave significantly higher grain yield compared to application of MRP alone.

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