Feed-Forward Control of Water and Nutrient Supply in Greenhouse Horticulture: Development of a System

Abstract

Minimisation of nutrient and water loss to the environment, prediction and planning of production and product quality, such that they meet the demands of customers, and increased financial return are some of the goals of current greenhouse horticulture. This requires an integrated system for monitoring and control of the nutrient solution, plant growth and product quality. This paper describes the components of such a system.Tomato was selected as example crop. Plant sensors for photosynthesis, radiation interception and fresh growth rate were developed and tested, and the combined plant-substrate model was validated against greenhouse experiments and commercial growth data. Techniques for auto-calibration of the crop model with sensor information were developed. Scenarios describing various fertigation regimes were defined, and a technique for the generation of set points for water and nutrient application on the basis of pre-defined optimisation goals was developed. These goals included drainage volume and nutrient concentration, nutrient application rate, fruit dry matter concentration, and fruit growth rate.The overall system was evaluated in a greenhouse experiment. In comparison with simulated 'normal' cultivation, optimisation of water and nutrient application indeed resulted in reduced application and drainage rates, increased fruit growth rate, and a dry matter concentration that met the optimisation goal. In conclusion, the monitoring and control system offers good prospects for efficient control of water and nutrient use, and control of crop growth in future control of greenhouse cropping systems. INTRODUCTIONCommon horticultural practice is to couple application of nutrients and water. Nutrient composition of the drain and substrate solution is usually analysed in an external laboratory every fortnight, on the basis of which the nutrient concentrations in the nutrient solutions are determined. During the next two weeks, recirculated drain and nutrient solutions are mixed until a certain electrical conductivity (EC) is reached. If the Na concentration in the drain reaches unacceptably high levels, drain is sluiced to the surrounding surface water. Increased crop transpiration leads to increased water and nutrient application. Applied nutrient quantities therefore usually exceed the needs of the crop. Moreover, possibilities to control crop growth and product quality by a regulated water and nutrient supply are not used by the growers. This approach leads to excess use of water and nutrients and their emission to the surrounding environment. The obvious solution is to supply water and nutrients based on the needs of the crop at each particular moment, which varies according to environmental conditions and crop development.Those issues were addressed in the 'Hydrion-Line' project. The basic principle

Simulating Growth and Development of Tomato Crop

“…Water uptake of the crop is calculated from transpiration and fresh weight growth as long as water availability is unlimited or it can be calculated based on the difference in water potential in the plant and the rooting medium (Marcelis, 1989;Elings et al, 2004).…”

Management of Greenhouse Crop Transpiration: The Way Forward

“…This approach would also improve model performance on a short time scale, and provide growers with insight in crop behaviour in the course of a day. A similar on-line approach for the selection of the optimum fertigation regime has proven to be effective (Elings et al, 2004).…”

“…Jointly, the two rates compose the instantaneous rate of potential water uptake by the root system. Simulated water uptake rate is under most circumstances equal to potential water uptake rate; and is lower only if water availability is insufficient, which can be simulated by combining the crop model with a substrate model (Elings et al, 2004).…”

Energy Saving in Greenhouses: Optimal Use of Climate Conditions and Crop Management

“…Based on models, control algorithms have been developed for on-line monitoring and control of the nutrient solution and plant growth (e.g. Elings et al, 2004). Essential for this system is the feedback of sensor information on plant performance.…”