Modelling Nutrient Uptake of Sweet Pepper

Models simulating dry matter production have been developed for a large number of greenhouse crops during the past decades. This paper describes how plant-nutrient relationships can be incorporated in a model for greenhouse crops, with sweet pepper as an example. Based on climatic data, the model simulates the growth of plant organs, transpiration, water uptake and uptake of the various macro nutrients. A mechanistic photosynthesis-driven model is used to simulate dry matter production. For each plant organ its required concentrations of the various macro nutrients are calculated, which depend on the ontogenetic age of the organ. The required nutrient uptake is calculated from these required concentrations and the dry weights of the organs. If there is no limitation in availability at the root surface the actual uptake will equal the required uptake. When the root system cannot fulfil the demand, uptake will be less, plant nutrient concentration will drop and crop production is potentially reduced. The model was tested on data from two different climatic regions (France and Spain). The model was also used to show some effects of the greenhouse climate on water and nutrient uptake. The rate of water uptake per unit radiation as well as the EC of the water taken up by plants was shown to vary considerably. Finally, the utilization of the model in an integrated control and monitoring system is discusse

Les stratégies de contrôle de la qualité sanitaire dans les Organisations de Producteurs de tomates

Our paper deals with free-riding issues in product safety control at the collective marketing level. It focuses on the empirical findings of the exhaustive face to face survey that has been conducted in 2007 by the authors with the quality managers of the tomato growers'unions of France. Our survey was supported by the National Tomato Charter, a regrouping of most of the French tomato growers'unions. Its aim was to identify the differences in monitoring and enforcement practices at the collective marketing level and to search for any group size effect on such practices. A main finding of our paper is that, beyond public regulation and collective rules imposed by the National Tomato Charter, POs implement voluntary control rules for a better control of free riding behavior within the group. Such additional rules differ both in monitoring intensity (measured by the number of pesticide residue analysis performed voluntarily by the group) and in sanction level (applied in case of deviation to the collective rule). Differences in safety control are not only triggered by customers specific requirements but also by group size (measured by the number of growers within the group). Eventually, our paper draws some perspectives for a more in-depth analysis of free riding issues. First, it calls for paying more attention to factors such as intra-group heterogeneity and differences in customers requirements. Second, it underlines the need for a more extensive analysis which includes safety control practices at the production level and wonders whether such practices are a complement or a substitute of control practices at the marketing level. ...French Abstract : Ce texte aborde les problèmes d'action collective dans le contrôle de la qualité sanitaire des produits avant leur mise en marché par les Organisations de Producteurs. Il est une synthèse des résultats de l'enquête menée auprès des responsables qualité de l'ensemble des OP adhérant à la Charte Nationale Tomate sur leurs pratiques de contrôle de la qualité sanitaire des tomates. L'enquête a eu le soutien des responsables de la Charte Nationale Tomate, qui regroupe la quasi-totalité de la production organisée en France. Elle avait pour objectif d'identifier la diversité des pratiques de contrôle au sein des OP et de mesurer l'effet de la "taille de l'OP" sur les modalités de contrôle mises en place. L'enquête montre qu'au-delà des règles communes imposées par la réglementation et la Charte Nationale Tomate, les OP mettent en place des démarches de contrôle diversifiées qui se différencient à la fois par l'importance de la surveillance (mesurée en nombre d'analyses de résidus de pesticides) et par le niveau des sanctions appliquées en cas de dérogation à la règle adoptée. Elle explique enfin la diversité de ces démarches, non seulement par les exigences de la clientèle mais aussi par la taille du groupe (mesurée par le nombre de producteurs). Notre rapport se termine par une discussion sur les améliorations à apporter à ce premier travail. Des précisions sont à apporter tout d'abord sur l'hétérogénéité intra et inter groupes et sur les niveaux d'exigences de la clientèle. Un complément d'analyse est ensuite nécessaire pour mieux caractériser l'effort de contrôle en amont du produit, au niveau de la production et pour étudier la complémentarité ou la substituabilité des deux types de contrôle: contrôle sur les pratiques en production, contrôle sur le produit.PRODUCERS' UNIOS; FREE-RIDING; MONITORING; ENFORCEMENT; CONTROL; PESTICIDE RESIDUES; TOMATO; FRANCE; ORGANISATIONS DE PRODUCTEURS; PASSAGER CLANDESTIN; SANCTION; CONTROLE; RESIDUS DE PESTICIDES; TOMATE

Development and evaluation of an automated prototype for the fertigation management in a closed system

In France, in order to prevent imbalances and accumulation of nutrients in the plant root zone, most of the soilless crops in glasshouses are cultivated in open drainage systems, which leads to water and fertilizer losses. The goal of the EU project CLOSYS (CLOsed SYStem for water and nutrient management) was to build a prototype which delivers water and nutrients according to the plant needs in a recirculating system. This prototype aimed at controlling production and quality as well as reducing nutrient accumulation or shortage in the root zone in a closed system and avoiding pollution of the environment. This paper deals with the development and the evaluation of the prototype in comparison with a classical closed system for a sweet pepper crop. This prototype includes: substrate and plant models incorporated in an expert system, using substrate and plant sensors, and a real time controller. Technical details and results of each module will be presented. The plant model provided proper simulations of growth and development parameters, nutrient concentrations in the plant organs, plant nutrient and water consumption. The expert system enabled the coupling between plant and substrate models, thus ensuring the system to take into account the weather forecasts. The real time controller managed to control relative water content and electric conductivity in the substrate slabs. A Leaf Area Index sensor was used to calibrate the plant model according to the real crop area development. As a conclusion, the CLOSYS system led to a lower nutrient consumption, lower sodium and chloride accumulation and a proper electric conductivity control in comparison with the classical closed system, while maintaining production and quality

Modelling dry matter production and partitioning in sweet pepper

Models predicting growth and yield have been developed for a large number of crops. This paper describes a dynamic, mechanistic model for sweet pepper, addressing issues such as leaf area expansion, dry matter partitioning and validation. Leaf area formation and organ initiation are simulated as a function of temperature sum. Light absorption and photosynthesis are calculated for a multi-layered uniform canopy. Leaf photosynthesis is calculated for the various leaf layers according to the biochemical model of Farquhar, and integrated to canopy photosynthesis. Net assimilate production is calculated as the difference between canopy gross photosynthesis and maintenance respiration. The net assimilate production is used for growth of the different plant organs and for growth respiration. Fruit set is simulated as a function of source and sink strength and temperature. Assimilate partitioning between vegetative parts and individual fruits is simulated on the basis of the concept of sink strengths. The sink strength of each individual fruit is calculated as a function of its temperature sum from anthesis. The sink strength of the vegetative parts is calculated as a function of temperature only. A wide range of experimental data show that leaf area is linearly related to the temperature sum from planting. The model was validated on the basis of six experiments in The Netherlands and France. Simulation of dry matter production and partitioning under a wide range of conditions showed that model results agreed well with measurements. Some directions for further improvements are discusse

CLOSYS: Closed system for water and nutrient management in horticulture

The EU project CLOSYS aimed at developing a CLOsed SYStem for water and nutrients in horticulture. The main objective was to control water and nutrients accurately such that pollution is minimized and crop quality enhanced. The closed system as developed in this project consists of crop growth models and substrate models, a new substrate, an expert system, a real time controller, fluorescence sensors, ion-selective sensors and a technical infrastructure. Plant model: Mechanistic models for rose and sweet pepper were build and self-learning capacity was introduced. The models simulate crop growth, and demand and uptake of water and individual nutrients. Plant sensor: A fluorescence imaging system was developed and tested to be used as an indicator for plant performance and stress factors. Nutrient sensor: An on-line multi-ion sensor measures the concentration of individual nutrients pH and EC of the recirculating water in the greenhouse. Substrate model: A 3D substrate model simulates the water and nutrient flows in the substrate depending on the root absorption and fertigation. Substrate: A rockwool substrate with improved physical and chemical properties was developed to allow a better control of water and nutrient fluxes in the root-zone. Expert system: The expert system, using model and sensor information and weather forecasts, determines a daily plan for fertigation. This plan contains the set-points for the real time controller. Real time controller: The real time controller controls the water and nutrient supply. It upgrades the fertigation parameters (irrigation EC, dose and frequency) to satisfy the set-points issued by the expert system, depending on current status of the system and on time constants and dynamic characteristics of the system. Technical infrastructure: All subsystems were integrated such that they can request data from the irrigation computer database. With these data, new set points for fertigation are calculated, whereafter the irrigation computer executes the requested tasks. Closed system: All components together form the closed system for water and nutrients. The performance of the closed system was compared to a standard sweet pepper growing system. The system has been running satisfactorily during a prolonged period (1 and a half year). Water and nutrient use, its availability in the rooting zone as well as the recirculating drainage water were controlled accurately