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Modeling

Development and Validation of a Phosphate Rock Decision Support System

Research and Market Development Division, IFDC, P.O. Box 2040, Muscle Shoals, AL 35662

^* Corresponding author (usingh{at}ifdc.org)

Received for publication August 23, 2005. Although some mathematical models exist to assist in deciding whether or not to apply phosphate rock (PR) to soils as a source of P, these models focused either on the use of highly soluble PR sources, mainly for pastures, or were too impractical for field use. There was, therefore, a need to develop a Phosphate Rock Decision Support System (PRDSS) with more comprehensive capabilities to predict the relative agronomic effectiveness (RAE) of PR with respect to water-soluble phosphorus (WSP) fertilizers at field and farm level. The PRDSS includes PR sources varying widely in solubility and different crop species grown on variable soil properties and rainfall conditions. In this paper, we describe the development and use of the mathematical model, PRDSS, to estimate RAE of PR sources with respect to WSP fertilizers and to calculate a simple index to be used for preliminary economic comparison of these two types of P sources. The PRDSS is able to function with a minimum input of only soil pH, the name of the mine that is the source of the phosphate rock, and the species of crop to be grown. A more accurate prediction of RAE is obtained from the PRDSS when more detailed data describing the soil, crop, and weather are included as inputs.

Abbreviations: AlC, crop species variance in tolerance to Al saturation • AlFC, free carbonate and Al saturation effect on relative agronomic effectiveness • CA, citric acid • DAP, diammonium phosphate • DSSAT, Decision Support System for Agro-Technology Transfer • EAlS, effective Al saturation • FA, formic acid • FC, free carbonate • MAP, monoammonium phosphate • NAC, neutral ammonium citrate • NAC₁, first extraction • NAC₂, NAC second extraction • PDSS, Phosphorus Decision Support System • PR, phosphate rock • PRDSS, Phosphate Rock Decision Support System • RAE, relative agronomic effectiveness • REE, relative economic effectiveness • REL, rainfall effect on leaching • SSA, sub-Saharan Africa • SSP, single superphosphate • SVI, substitution value index • TSP, triple superphosphate • WSP, water-soluble phosphorus

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