Simulation of nutrient uptake by plants from hydroponics as affected by salinity buildup and transpiration

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⁺, NO ₃^--N, NH₄⁺-N, PO₄-P, Ca²⁺, Mg²⁺ and SO₄^2-, whose influx parameters are affected by Na and Cl^-, but not with time (age). Sodium influx is passive above a critical concentration. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model was tested against K⁺ uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. The model was used to simulate ion interaction in uptake and shoot and root growth. The importance of Ca under saline conditions was clearly demonstrated.