Calibration and sensitivity analysis of a dynamic model for control of nitrate in lettuce

Soluble carbohydrates and nitrate in the cell sap of leafy vegetables act a s complementary osmotic solutes to maintain the plant's turgor pressure. Th e implication is that nitrate at harvest time can be kept low by manipulati ng the source-sink balance. Pseudo-static calculations based on a model dev eloped earlier fairly well reproduced the seasonal variability of nitrate l evels in crops grown and harvested at near-monthly intervals. This paper co ncentrates on the dynamic behaviour of this model by calibrating it to avai lable data of lettuce growth, and by performing a sensitivity analysis. The model contains inhibition functions which are activated when the intern al assimilate carbon concentration is near an upper or lower limit, in orde r to restrict photosynthesis or growth, respectively. Sensitivity analysis and calibration contour plots reveal that estimates of the growth parameter s have a large uncertainty when growth is limited by carbon availability. I n regions that are of interest for nitrate control, i.e. in the sink-limite d case, all parameters determining the source-sink balance are important. C onsequently, experiments must be designed such that they cover sink-limited conditions.