Hydric and nutrient element nutrition of a tomato crop on rockwool: Ionic interrelationships

Abstract

The hydric and nutrient element nutrition of tomato plants (cv. Rambo) cultivated in a greenhouse on rockwool was studied by following the daily net uptake by the plant of nutrient elements and water and the changes occurring in the nutrient solution and drainage solution in order to establish the actual demand of the plant for each nutrient element and the relation between the uptake of each ion with the uptake of other ions under the agriclimatic conditions of this experiment. In this way, we attempted to optimize the fertigation program to increase the final size and quality of the crop. The accumulative uptake of water and nutrient elements by plants over the whole cultivation period, from 20 days after transplanting, fits quadratic curves since the absorption rates increase constantly as the plant develops (positive quadratic term), particularly those which are present in excess in the irrigation water (larger quadratic term). The slopes of the curves corresponding to nutrient element uptake increased in the following order: nitrate, potassium, and calcium (the same order as that in the leaf). The results demonstrate that water uptake is closely related with calcium and potassium ion uptake and that there is a reciprocal relationship in the uptake of the potassium‐ammonium and phosphate‐nitrate pairs. The absorption of magnesium was related to the uptake of sodium and chloride, and the uptake of sulphate and chloride was not related to the uptake of the other ions. Under the study conditions, the optimum daily values for net consumption per plant from 40 days onwards can be established as 1.5–2.0 L of water, 25–28 mmoles of nitrate, 14–16 mmoles of potassium, 10–12 mmoles of calcium, 3.0–3.5 of phosphate, and around 3.0 mmoles of ammonium.