Comparative Study of Different Nitrogenous Fertilizers on their Mineralization in Submerged Rice Soils*

Incubation studies on mineralization of slow-release N fertilizers, ammonium sulphate and urea under waterlogged soil conditions with red soil of Mirzapur and alluvial clayey soil (Karail) of Azamgarh districts of Uttar Pradesh showed that the ammoniacal N increased during the first four weeks of submergence and afterwards it tended to decrease. The magnitude of release of NH₄+-N from various sources was in the order: (NH₄)₂SO₄ > urea > lac coated urea > sulphur coated urea for both the soils. Less than 50 per cent of the original N was released as NH₄+-N by the slow-release N fertilizers. The decreases were appreciably noted in the case of (NH₄)₂SO₄ and urea treated soils as compared to sulphur coated urea andlac coated urea, and the decrease was very much pronounced in the case of red soil. Much loss of N occurred from (NH₄)₂SO₄ and urea in comparison to sulphur coated: urea and lac coated urea. The content of NO₃⁻-N after submergence decreased, but after two weeks it fluctuated during the incubation period. Very less amount of added N appeared as NO₃⁻-N.