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Modern fertilization recommendations must optimize crop yield and quality and minimize chances of negative environmental effects due to overfertilization. Data from fertilizer studies can be fitted to several mathematical models to help determine optimum fertilizer rates, but resulting recommendations can vary depending on the model chosen. In this research, lettuce ( Lactuca sativa  L.) was used as a case study vegetable crop to compare models for estimating fertilizer N requirements. Greenhouse studies were conducted with `South Bay' and `Sierra' cultivars of crisphead lettuce to measure yield response to applied N. Individual plants were grown in pots and received six rates of N (0.0, 0.2,0.4,0.6,0.8, and 1.0 g/plant) as ammonium nitrate in split applications. Data for plant fresh mass and N uptake were recorded. The logistic model described the data for both cultivars quite well, with correlation coefficients of 0.98 and above. The logistic model was also applied to field data for average head mass of `South Bay' lettuce following application of N at 0,56,112,168,224, and 280 kg·ha -1 . Logistic, linear-plateau, and quadratic models were compared for the field data. Coefficients for the linear-plateau model were derived from the logistic model. All three models for lettuce production were compared graphically and analytically. The model coefficients were then used to make improved estimates of fertilizer recommendations for field production of lettuce.

A Comparison of Three Mathematical Models of Response to Applied Nitrogen: A Case Study Using Lettuce