Nutrients and toxic substances accumulation in the plant and their effect on uptake: Simulation study in hydroponics

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested to simulate nutrient uptake by plants grown in hydroponics with recycled solutions. The model accounts for salinity accumulation with time and plant growth and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. Influx, as a function of the ion concentration, is according to Michaelis-Menten active mechanisms for K⁺, NO₃ ^--N, NH₄⁺-N, PO₄-P, Ca²⁺, Mg²⁺ and SO₄^2-. Influx parameters are affected by the accumulation of these ions and Na⁺ and Cl^- in the plant. Sodium influx is passive above a critical concentration. Salinity (due to Na concentration) suppresses root and leaf growth, which further affects uptake and transpiration. The model was tested against K and N uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. The model was used to simulate ion interaction in uptake, shoot growth, root growth, and the effects of nutrient accumulation in the plant on uptake. The results indicated that N uptake and content in the plant are most sensitive to interactions with NaCl salinity.