| heal.abstract |
Based on a mass balance equation in closed-loop hydroponic systems, a model relating the Na or Cl concentration in the drainage solution to the cumulative uptake of water may be established. This model might be used as a component of an integrated intelligent automation system to minimize the need to discharge drainage water, thereby reducing groundwater contamination. The above model, which was validated and tested in closed hydroponic crops of cucumber, bean and pepper, is based on a differential equation with three variables, particularly the concentration of Na or Cl in the recycled drainage solution, the cumulative volume of water consumed by the crop and the uptake concentration of Na or Cl. Based on experimental data from the cucumber crop and applying regression analysis, both a linear and an exponential relationship were established between the uptake concentration of Na or Cl and the concentration of the corresponding ion in the root zone (drainage water). Using these relationships, the uptake concentration was replaced by the concentration of Na or Cl in the root zone, thereby obtaining a differential equation with two variables in each case, which related the Na or Cl concentration in the root zone with the water uptake. In this paper, we compare the curves predicted by the above model in the cucumber crop when the relationship between the uptake concentration of Na or Cl and the concentration of the corresponding ion in the root zone was considered either linear or exponential. Furthermore, we examine the impact of the volume of nutrient solution per plant in the closed system (drainage water plus nutrient solution retained by the substrate) on the pattern of Na or CI accumulation in the root zone. Finally, we explore the impact of the parameters obtained by nonlinear regression analysis, which depend mainly on the plant species, on the curves predicted by the proposed model. |
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