INTERATIONS BETWEEN NITRATE (NO3) AND CHLORIDE (CL) IN NUTRIENT SOLUTIONS FOR SUBSTRATE GROWN TOMATO

Abstract

In two successive experiments tomato was grown at different Cl and NO3 concentrations in the root environment with rockwool as a sub-strate. The EC value in the nutrient solution was fairly constant, varying between 3.5 and 4.0 dS m-1 in all treatments. The NO3 concentrations in the treatments varied between 0 and 25 mmol L-1, with a step-wise replacement of NO3 by an equivalent Cl concentration. With the crop grown in winter-spring the yield was reduced at a low N-supply, but with the crop grown in summer-autumn no significant difference was found in the range of the NO3 concentrations between 1 and 25 mmol L-1. Blossom-end rot decreased and gold speck increased with increasing Cl/NO3, indicating an improved Ca uptake. This was confirmed by the results of the tissue tests, which showed higher Ca contents with increasing Cl/NO3. The reasons for this increased Ca uptake are discussed, but could not really be explained by the data collected. It seems clear that tomato can be grown at rather low NO3 and high Cl concentrations in the root environment and this pro-vides opportunities to lower NO3 concentrations in the drain-off and a consequent reduction of environmental pollution. This is of great interest, especially with crops grown at a high EC value like tomato