Model guided calibration: Nitrogen in cauliflower

NICOLET is a single organ, three-state-variable vegetative model, originally developed for lettuce, with focus on the compositional relationships among water, carbon and nitrogen, in their various forms (soluble, structural, organic, etc.). It recognizes the decrease with age of organic N content, dry matter content, and specific leaf area. At the same time, plant nitrate concentration responds to changes in the environment, particularly in the nutrient solution. In this study, the NICOLET model is fitted to data from a two-year N-nutrition experiment with cauliflower. Compared to previous calibration attempts, the new data are for a crop different than lettuce and include leaf area measurements. Since the model has many parameters (twenty-four in this version), a balanced treatment of all of them may end up in one of many local extrema. Therefore, a first-order calibration, in stages guided by the structure of the model, is used, fitting only a few parameters at a time. This approach results in good fits, for both years with the same set of parameters, of total dry matter, dry matter content, reduced-N content and specific leaf area. However, a good prediction of nitrate concentration requires a different parameter set for each year.