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MODELING

Comparison of Three Statistical Models Describing Potato Yield Response to Nitrogen Fertilizer

^a Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd., Sainte-Foy, Québec, Canada, G1V 2J3
^b McCain Foods Limited, Florenceville, New Brunswick, Canada, E7L 3G6
^c Atlantic Cool Climate Crop Research Centre, Agriculture and Agri-Food Canada, 308 Brookfield Road, P.O. Box 39088, St. John's, Newfoundland, Canada A1E 5Y7
^d Potato Research Centre, Agriculture and Agri-Food Canada, P.O. Box 20280, Fredericton, New Brunswick, Canada E3B 4Z7

belangergf{at}em.agr.ca

Estimation of optimum fertilizer rates is of interest because of growing economic and environmental concerns. Optimum fertilizer rates can be determined by fitting statistical models to yield data collected from N fertilizer experiments. We evaluated quadratic, exponential, and square root models describing the yield response of potato (Solanum tuberosum L.) to six rates of N fertilization (0–250 kg N ha^-1) with and without supplemental irrigation at four on-farm sites in each of three years (1995 to 1997) in New Brunswick, Canada. Economic optimum N rates (N_op) varied among sites and models. The proportion of variability (R²) explained by the three models was similar. The quadratic model, however, calculated a greater N_op value (175 kg N ha^-1) averaged over all sites than those calculated by the square root (123 kg N ha^-1) and exponential (80 kg N ha^-1) models. Regression residues of the quadratic model were closer to a normal distribution than those of the other two models, indicating a less systematic bias. Economic losses were greatest when the quadratic model was the most appropriate model, but the data were fitted to the exponential (loss of $204–240 ha^-1; all values in Canadian dollars) or square root model (loss of $58–201 ha^-1). We conclude that the quadratic model is the most appropriate for describing the potato yield response to N fertilizer and predicting N_op for areas with a ratio of the cost of N fertilizer to the price of potatoes similar to that in Atlantic Canada.

Abbreviations: N_op, optimum N rate • SE, standard error of the estimate

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