QUEFTS can be used for quantitative evaluation of the native fertility of tropical soils, using calculated yields of unfertilized maize as a yardstick. The procedure consists of four successive steps. First the potential supplies of nitrogen, phosphorus and potassium are calculated, applying relationships between chemical properties of the 0-20 cm soil layer and the maximum quantity of those nutrients that can be taken up by maize, if no other nutrients and no other growth factors are yield-limiting. In the second step the actual uptake of each nutrient is calculated as a function of the potential supply of that nutrient, taking into account the potential supplies of the other two nutrients. Step 3 comprises the establishment of three yield ranges, as depending on the actual uptakes of nitrogen, phosphorus, and potassium, respectively. Next, these yield ranges are combined in pairs, and the yields estimated for pairs of nutrients are averaged to obtain an ultimate yield estimate (Step 4).
The QUEFTS model works only for a maize crop. The generic version of QUEFTS is called CROPFERT and can be used for all type of crops, for which the nutrient concentrations are given in the file NUTRIDAT.dat
Yields under nutrient limited conditions, actual crop uptake of nitrogen, phosphorus and potassium, recovery of applied fertilizer nutrients, yield increase from fertilizer application
QUEFTS can be used to calculate the nutrient limited yields for crops growing under tropical conditions. This requires either soil chemical data or representive crop experiments to derive the base nutrient supply of unfertilised soils. This base nutrient supply is used to calculate the actual crop nutrient uptake and yields for the main crops. If fertilizer nutrients are applied, the resulting increases in crop nutrient uptake and yields can next be calculated.
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