AbstractOne approach for the development of fertilizer recommendations is based on field-measured yield response to added fertilizer.The crop nutrient requirement (CNR) is the total amount of that element needed by the crop during the production season to produce optimum economic yield, and is equivaient to the fertilizer rate above which no significant increase in yield occurs. Published and unpublished fertilization research done in Solanaceae, tomato (Lycopersicon esculentum), eggplant (Solarium melongena), and sweet pepper (Capsicum annuum), in Puerto Rico over the past 25 years was used to calculate CNR values for nitrogen (N), phosphorus (P) and potassium (K). The mean yields obtained from each fertilizer treatment were converted from a unit area basis (ton/ha or kg/ha) to percentage relative yield (RY). The RYs were then plotted against rates of nutrient applied and fitted to linear, quadratic, linear-plateau, quadratic-plateau, exponential, and Cate-Nelson models to determine CNR values. Plant response to K was not observed in soils dominated by 2:1 clays (2:1 clay soils). Large variability and few experimental data points precluded fitting equations to the data in soils dominated by 1:1 clays (1:1 clay soils). For P and N, predicted CNR values varied widely, depending on the selected model. The best model was selected on the basis of coefficients of determination, standardized residual plots, and was corroborated with economic returns. For 1:1 clay soils, predicted CNR values were 113 and 255 kg P2Os/ha and 150 and 207 kg N/ha for the Cate-Nelson and quadratic models, respectively. For 2:1 clay soils, predicted CNR values were 50 and 148 kg P205/ha for the Cate-Nelson and finear- plateau models, respectively, and 50 and 120 kg N/ha for the Cate- Nelson and exponential models, respectively.
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