Effects of EC and fertigation strategy on water and nutrient uptake of tomato plants

In this study, water and nutrient uptake from the substrate and responses of the crop to fertigation strategies were analysed. In an experiment and simulation study, the amount and frequency of fertigation and electrical conductivity (EC) of the fertigation water were changed for a tomato crop grown on rockwool. In a climate chamber, tomato plants were grown on rockwool while five different EC levels and two fertigation frequencies were maintained. Effects on plant growth, water uptake, and nutrient uptake were measured. The experimental data were compared with simulated results. We used two simulation models: a plant growth model and a model that describes water movement and nutrient transport within the substrate, i.e. rockwool, and root uptake of water and nutrients from the substrate. The key idea behind the simulation of uptake of water and nutrients is to consider transport (mass flow and diffusion) from the bulk substrate surrounding the roots towards the root surface. Water uptake may also be hindered due to osmotic potential differences between substrate solution and root sap. The results confirmed the hypothesis that at lower EC growth is reduced due to limitations in nutrient availability (transport rate towards the root) while at higher EC growth is reduced mainly due to water stress (low osmotic potential). INTRODUCTION The goal of managing water and nutrient supply to greenhouse crops is to control crop growth and product quality as well as to minimise losses of water and nutrients to the environment. Precise supply of water and nutrients is necessary to reach this goal, where supply of water and the individual nutrients is in proportion to the demand of the crop. In order to do so, quantitative information on demand and uptake of water and the individual nutrients is required. Information on crop behaviour when either of them is in surplus or in shortage is also necessary. Knowledge of the transport of water and nutrients from the bulk substrate towards the root surface must be known in order to determine whether the plant demand can be fulfilled or not (shortage). Such information could be obtained from a large number of experiments, but a simulation model in combination with a limited number of experiments is a more powerful tool for such an analysis. The electrical conductivity (EC) of the nutrient solution as well as the amount and frequency of fertigation (irrigation with nutrient solution) are the most important variables used by growers to control the supply of water and nutrients to the crop. The aim of this study was to analyse the water and nutrient uptake from the substrate and the responses of the crop to fertigation strategies. In an experiment and simulation study, the amount and frequency of fertigation and EC were changed to explore the following two hypotheses for a tomato crop grown on rockwool: Crop growth reduction may occur at both low and high EC. At low EC, not enough nutrients may be available to the roots (unless in a well-mixed water culture) resulting in a reduction of nutrient uptake, which may result in reduced crop growth. At high EC, ample nutrients are available. However, reduction of water uptake may Proc. 4 IS on Cropmodels Eds. J.H. Lieth & L.R. Oki Acta Hort. 593, ISHS 2002