Saturday, 15 July 2006

Effect of Different Compacted Phosphatic Fertilizers on Enzymes Activity in.

C.A Srinivasamurthy, M.V. Ravi, Sujata F Harlapur, G.N. Thippeshappa, A.S. Kumaraswamy, S. Bhaskar, N.G. Basavaraju, B. Gayathri, M.N. Ravikumar, K.G. Ankegouda, M.V. Bhargavi, G. RAVI, V.R. Ramakrishna Parama, and R. Siddaramappa. Univ of Ag Sciences, Gandhi Krishi Vignana Kendra, UAS, Bangalore, 560 065, India

A pot experiment was conducted to study the changes in the acid phosphatase, urease and dehydrogenase enzymes activity of soil due to incorporation of compacted rock phosphates to low pH soil under flooded condition and to a neutral arable soil. The low pH soil was collected from a farmer's paddy field (Isohyperthermic, kaolinitic paleustults) located in the western ghats of Karnataka which receives about 2500 mm annual rainfall. The neutral soil was collected from a University Research Station near Bangalore. The experiment consisted of 15 treatment combinations with compacted rock phosphates prepared by compaction of Jamarkotra Phosphate Rock (JPR) with Mono Ammonium Phosphate (MAP and Sulfur (S) and also water soluble and insoluble P sources. After incorporating recommended dose of these P sources to rice soil under submergence and the neutral soil at field capacity, the activity of enzymes was estimated at tillering, panicle initiation, flowering and harvest stage of each crop after incubation following standard procedures. Under submergence, the activity of acid phosphatase exhibited a gradual decrease from tillering stage upto harvest. While urease activity showed a two-fold increase from tillering to panicle initiation stage and a sudden decrease thereafter, the dehydrogenase activity reflected a three-fold increase from tillering to flowering followed by a sudden decrease at harvest. In the neutral soil no much change in acid phosphatase activity occurred during the growth stages of crop, while urease activity decreased with crop growth and the dehydrogenase activity of soil increased. At harvest stage, the compacted JPR (A) + MAP + S recorded higher activity of phosphatase (80.63 ug PNP/g/hr), urease (31.70 ug/g/hr) and dehydrogenase (37.72 ug TPF/g/hr) in low pH soil under submergence and the corresponding values in neutral arable soil were (78.26), (18.43) and (20.84) respectively compared to other P fertilizers. The enzymes activity recorded in flooded acidic soil was slightly higher compared to non-flooded neutral soil. The increase in activity may be related to higher organic matter content of soil, rise in soil pH towards neutrality due to flooding. Further, the release of P from phosphate rocks increased the enzymes activity whereas the water-soluble sources diminished the same. Among non-compacted sources, Gafsaphos recorded higher activity but among compacted sources, JPR (A) + MAP + S recorded higher activity compared to other phosphate rocks

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