Fertilization decision model – a synthesis of soil and plant parameters in a computerized program

A fertilization decision model is suggested, based on soil and plant parameters. The optimum concentration range of nitrate nitrogen in the soil solution, during the uptake period of the growing plant, is 50–250 ppm N-NO₃for all soils and plants. The optimum bicarbonate-soluble P varies with plant and soil type, and is determined by response experiments. Percent recovery of added fertilizer by bicarbonate extraction is used to calculate the amount of fertilizer needed to raise the extraction value to the optimum level. Exchangeable potassium is considered to be the only source important during the growing season of an annual crop. The main plant parameters are the uptake rate of nutrients during the growing season, depth of root penetration, and sensitivity to ammonium. The model calculates, at preset time intervals, the balance between the quantity of nutrients in the root zone and uptake by plants. A decision to add fertilizer is made if a deviation from the optimum exceeds a predetermined value.