Comparison of three statistical models describing potato yield response tonitrogen fertilizer

Estimation of optimum fertilizer rates is of interest because of growing ec onomic and environmental concerns. Optimum fertilizer rates can be determin ed by fitting statistical models to yield data collected from N fertilizer experiments. We evaluated quadratic, exponential, and square root models de scribing the yield response of potato (Solanum tuberosum L,) to six rates o f N fertilization (0-250 kg N ha(-1)) with and without supplemental irrigat ion at four on-farm sites in each of three years (1995 to 1997) in New Brun swick, Canada. Economic optimum N rates (N-op) varied among sites and model s. The proportion of variability (R-2) explained by the three models was si milar. The quadratic model, however, calculated a greater N-op value (175 k g N ha(-1)) averaged over all sites than those calculated by the square roo t (123 kg N ha(-1)) and exponential (80 kg N ha(-1)) models. Regression res idues of the quadratic model were closer to a normal distribution than thos e of the other two models, indicating a less systematic bias. Economic loss es were greatest when the quadratic model was the most appropriate model, b ut the data were fitted to the exponential (loss of $204-240 ha(-1); all va lues 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 t he 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 th at in Atlantic Canada.