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Content archived on 2024-05-07

Optimal control of nitrate accumulation in greenhouse lettuce and other leafy vegetables

Objective

Summary of the proposed NICOLET project High concentrations of nitrate in leafy vegetables such as lettuce constitute a health hazard. Out of concern for consumer safety, the EC issued a directive (194/97), defining maximum levels for nitrate in fresh vegetables, including lettuce and spinach. At present, low light levels in winter often make it difficult for growers to meet the required standard. A generally applicable method, incorporating both accurate control of the internal nitrate concentra- tion and an optimal production management strategy, is as yet not available. The aim of this project is to establish cultivation methods for accurate control of nitrate accumulation in leafy vegetables. The nitrate concentration in lettuce is negatively correlated with the level of soluble sugars. Thus, increased sugar concentrations, associated with stimulated photosynthesis at higher light levels, lead to lower nitrate concentrations in lettuce. The proposed project is based on the hypothesis that several different environmental factors can be manipulated to control the nitrate concentration in the crop. This is based on the understanding that the level of soluble sugars in plants is determined by the balance between carbohydrate supply (photosynthesis, mobilization) and demand (growth, respiration, storage), rather than by photosynthesis alone. A preliminary mathematical model based on this hypothesis was formulated, which was already able to simulate published results of seasonal effects on the nitrate concentration in lettuce with reasonable accuracy. A fully developed version can find practical application as a crop management tool, advising the grower about the effects of variable weather conditions on crop nitrate accumulation and predicting effects of adjustments in greenhouse climate settings and fertigation scheme. In addition, optimal cultivation management strategies can be calculated on the basis of model predictions, which will help growers to achieve the best possible result within the limits of Community regulations on nitrate in vegetables, without requiring large investments. Application of more elaborate versions, involving on-line control of both root and shoot environment, should result in a considerably enhanced degree of control of the cultivation process. In the proposed project, we envisage to elaborate and expand on a novel and encouraging preliminary line of research. In the initial stages, the project will concentrate on validation and sensitivity analysis of the preliminary model, as well as experimentation to establish time constants for the dominant physiological processes. Besides, additional methods to decrease nitrate accumulation will be tested. Depending on the outcome of the experimental research, there may be a need to add detail to the model. In addition, different modules will be developed to enhance the model, enabling it to predict the effects of various specific environmental disturbances. In parallel with the development of the model, optimal control scenarios will be calculated and tested, both for off-line and on-line applications of the model.

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Topic(s)

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Funding Scheme

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Coordinator

RESEARCH STATION FOR FLORICULTURE AND GLASSHOUSE VEGETABLES
EU contribution
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Address
Linnaeuslaan 2a
1431 AALSMEER
Netherlands

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Total cost

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Participants (3)

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