Titratable Acidity to Estimate Ammonia Retention1
- R. C. Izaurralde,
- D. E. Kissel and
- M. L. Cabrera2
Simulation models of fertilizer behavior in soils are potentially useful tools to improve fertilizer use efficiency. Presently, there are no satisfactory models that describe NH3 retention in soils. In order to develop such a model, a better understanding of how soils retain NH3 and a quantitative measure of soils' NH3 retention capacity are needed. We compared soil cation exchange capacity (CEC) and several measures of soil titratable acidity for predicting the amount of NH3 retained in the center of a band resulting from anhydrous NH3 application to soil. The titratable acidity to pH 9 estimated with NH4OH was a much better predictor than CEC of the NH3 retained. In some soils, the pH in the center of an NH3 retention zone differed slightly from pH 9, resulting in some error in estimating the NH3 retained. This error was greatest on a salty soil because of the small slope of the buffer curve near pH 9. We found soil titratable acidity to be stoichiometrically related on a 1:1 basis to the amount of NH3 retained. Apparently, CEC is a poor predictor of the amount of NH3 retained by soil because many of the cation exchange sites do not participate in a soil's capacity to adsorb NH3. Since a soil's titratable acidity to pH 9 is a stoichiometric predictor of NH3 retention capacity in soils, it may be used to more easily model the properties of an NH3 retention zone as affected by factors such as N fertilizer rate applied, spacing between application points, and soil bulk density.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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