Jf. Willcutts et al., A COMPARISON OF 3 MATHEMATICAL-MODELS OF RESPONSE TO APPLIED NITROGEN- A CASE-STUDY USING LETTUCE, HortScience, 33(5), 1998, pp. 833-836
Modern fertilization recommendations must optimize crop yield and qual
ity and minimize chances of negative environmental effects due to over
fertilization. Data from fertilizer studies can be fitted to several m
athematical models to help determine optimum fertilizer rates, but res
ulting recommendations can vary depending on the model chosen. In this
research, lettuce (Lactuca sativa L.) was used as a case study vegeta
ble crop to compare models for estimating fertilizer N requirements. G
reenhouse studies were conducted with 'South Bay' and 'Sierra' cultiva
rs of crisphead lettuce to measure yield response to applied N. Indivi
dual 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 applicati
ons. Data for plant fresh mass and N uptake were recorded. The logisti
c model described the data for both cultivars quite well, with correla
tion coefficients of 0.98 and above. The logistic model was also appli
ed to field data for average head mass of 'South Bay' lettuce followin
g application of N at 0, 56, 112, 168, 224, and 280 kg.ha(-1). Logisti
c, linear-plateau, and quadratic models were compared for the field da
ta. Coefficients for the linear-plateau model were derived from the lo
gistic model. All three models for lettuce production were compared gr
aphically and analytically. The model coefficients were then used to m
ake improved estimates of fertilizer recommendations for field product
ion of lettuce.