Pollution Research Paper

Vol. 36, Issue 4, 2017; Page No.(918-924)

REACTION RATE CONSTANTS FOR UREA TRANSFORMATIONUNDER FLOODED CONDITIONS

VANITHA S., V. RAVIKUMAR AND T. SHERENE JENITA RAJAMMAL

Abstract

The main form of fertilizer applied to lowland rice is urea, but very few researches are conductedon its movement and transformations under flooded soil conditions. An in-situ study wasconducted to measure movement and transformation of urea in flooded soils. Urea transformationis difficult to model in flooded soil systems due to the complicated transformations it undergoes.An essential step in analytical modelling is the determination of model parameters such as reactionrate constants. In order to estimate the reaction rate constants, an experiment was conducted in asoil spiked with urea in glass containers and the soil moisture and temperature were maintainedin the field condition. In this study only ammonium volatilized is captured and analysedperiodically. The nitrate content in the glass container was found out at the end of the experiment.The reaction rate constants were estimated by solving the partial differential equationsrepresenting urea reactions in a two step process using risk solver platform in the MS-Excelenvironment. The method was found to have minimum number of observations withoutestimating the urea, ammonium and nitrate in soils periodically. The estimated reaction rateconstant for ammonia volatilization was found to give a good estimate of volatilized ammonia withthat of the observed volatilized ammonia. The estimated reaction rate constant of urea hydrolysis,distribution coefficient, volatilization, nitrification and denitrification are 0.0022 h-1, 0.9, 0.0081 h-1, 0.0010 h-1 and 0.0436 h-1respectively. The reaction rate constants estimated in this study are usefulfor Nitrogen balance studies in flooded soils.

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