UPTAKE RATES OF NO₃ AND K BY LETTUCE ON SOILLESS CULTURE: A MATHEMATICAL MODEL AND EXPERIMENTAL RESULTS

A model is presented for water and nutrient recycle and uptake by plants grown in a soilless culture. The growth system consists of a channel, filled with a non-absorbing substrate, tilted in a given slope. The nutrient solution is applied via emitters (drippers) of given discharge rates and distances. The solution flows according to the hydraulic head gradient and conductivity, in the saturated portion of the substrate only, and drains to a reservoir at the end of the channel; transpiration losses are then compensated with water, which contains nutrients and saline substances. The solution then would be recycled to the system. Uptake is accounted for NH₄-N, NO₃-N, K, PO₄-P, SO₄-S, Ca, Mg, Na, Cl and HCO₃, balanced by atmospheric CO₂. The model was calibrated with data of lettuce grown in sandy soil. Simulated N uptake somewhat exceeded, but K uptake agreed with actual uptake by the plants. The model may be a useful tool to design and manage the system based on the crop potential needs for water and nutrients, and of water quality.