Evaluation of the Nicolet Model for Simulation of Short-term Hydroponic Lettuce Growth and Nitrate Uptake

Accurate simulation models for short-term (∼hours) changes in hydroponic crop growth and nitrate uptake are needed for rapid fault detection in hydroponic systems. Comparison between model-predicted and measured values for crop growth and nitrate uptake is proposed as the basis for such a fault detection system. To this end, the Nitrate Control in Lettuce (NiCoLet) model was used to evaluate both short- and long- term changes in growth and nitrate accumulation. Three replicated experiments were conducted with lettuce (Lactuca sativa L. cv. Flandria), including: (1) plants subjected to either low or high nitrate concentration treatments for model calibration; (2) collection of growth data every 2 days for model validation; and (3) frequent (every 4 mol m^-2 of accumulated light) collection of growth and shoot nitrate concentration data to validate short-term predictions. After a minor modification (maximum nitrogen uptake rate restricted) and calibration, the NiCoLet model accurately simulated lettuce crop growth and nitrate uptake on a long-term basis and provided evidence of short-term behaviour, including statistically significant predictions of diurnal patterns. This is a first step in realising fault detection systems based on mechanistic simulation models.