|Authors: ||I. Seginer, R. Linker, F. Buwalda, G. van Straten, P. Bleyaert|
|Keywords: ||lettuce, Lactuca sativa, growth, nitrate content, nitrogen stress, ontogenetic change|
The NICOLET model has been developed to predict the growth and nitrate content of greenhouse lettuce.
Four single-organ versions have been developed:  abundant supply of nitrogen (1998),  mild N-stress (1999),  severe N-stress (2003), and  ontogenetic changes of organic-N and water content (in preparation). The ‘abundant-N’ model  and the ‘mild-stress’ model  have two compartments: ‘structure’ and ‘vacuole’, while the ‘severe-stress’ model  requires a third compartment: ‘excess-carbon’, and the ‘ontogenetic’ model  has separate ‘metabolic’ and ‘support’ structural sub-compartments.
The main special features of the NICOLET model are  the osmotica balance of the ‘vacuole’, where nitrate and hydrocarbons play a complementary role in maintaining a constant osmotic potential,  the excess-carbon compartment, where ‘dry’ carbon compounds are stored, and  the sub-division of the ‘structure’ into sub-compartments of different compositions.
Loosely speaking, the first feature controls the nitrate concentration, the second controls the organic-N and water contents, and the third controls the ontogenetic changes.
The NICOLET model has been able to mimic ‘normal’ seasonal variations of nitrate content, as well as the effects of drastic N-stress treatments.
These results are illustrated by comparing measured data with model-simulations.
Accurate prediction of nitrate concentration is difficult, due to its sensitivity to changes in the environment.
Exact control of nitrate under commercial conditions may require transient corrective measures, such as N-interruption, in conjunction with a good plant-nitrate monitoring system.
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