Greenhouse Evaluation Of Transformation Of N15 Enriched Urea Under Varying Management Systems: II: Determination of the Rates of Reactions

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Obiagwu C. J.
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A greenhouse study was conducted to evaluate the effect of placement methods, chemical and physical amendments as well as time of sampling on the rate of nitrification and hydrolysis reactions of urea used to fertilize maize. The solution or equilibrium ureolysis products consisting of urea-N(NU), NH.N(Na) and No,-N(Nn) were used for the evaluation of the total nitrate and ammonium necessary for the derivation of such reaction rates. Freudlich absorption laws were applied. The nitrification rate was therefore, the total concentration of Nn including those estimated to have been taken up by the plant divided by time (TNn/dt); hydrolysis reaction rate was the change in concentration of Na in the exchange complex plus that in solution divided by the change in time, (TNI/dt).Broadcast application method without chemical amendments gave the highest rates of reaction. The physical and chemical modifications such as the use of super-granulation or chemical additives made it difficult to predict when hydrolysis or nitrification reactions would be completed. The nitrification reaction rates were greater than hydrolysis rate for UBA and IBDU-BRY treatments while the converse was observed for UBR and N+UBR treatments. The two reaction rates are equal when supergranules were used.
East African Agricultural And Forestry Journal, 57 (nos 3&4), p. 231-237