Chloride interaction with nitrate and phosphate nutrition in tomato (Lycopersicon esculentum L.)

Tomato plants were grown in a greenhouse in 100 liter containers containing nutrient solutions. A 4 × 3 × 3 factorial experiment of Cl × N × P was conducted. The Cl^‐ concentrations were 0, 10, 35 and 70 meq/1; NO^‐ ₃ concentrations were 7.5, 15, and 20 meq/1; and H₂PO^‐ ₄ concentrations were 1, 2, and 5 meq/1. Fifteen different plant parameters were analyzed. There was a decline in dry matter yield with increasing Cl^‐ concentration in solution at all NO, and H₂PO^‐ ₄ levels. The effect of NO^‐ ₃ levels on dry matter at each Cl^‐level was varied and resulted in a significant Cl^‐ x NO^‐ ₃ interaction. The Cl^‐ affected all measured plant parameters but K and P content in the plant. Chloride content in the plant was depressed by increasing NO^‐ ₃ concentration in the solution at all levels of Cl^‐ in the solution. There was a little effect of H₂ PO^‐ ₄ on Cl^‐ and Mg content in the plant. The possibility of using NO^‐ ₃ fertilizers to depress Cl^‐ uptake by the plants is discussed.

Interaction between solution salinity and plant nutrition was investigated for several crops by Bernstein et al. (1974). Their experiments were conducted at relatively low nutrient solution concentrations which contained only 2 and 4 meq/l of NO^‐ ₃. Low NO^‐ ₃ concentrations are justified when very low C1^‐ concentrations are present in solution. Letey et al. (1982) did not find any response of tomato to increases in NO^‐ ₃ concentration beyond 1 meq/l in a chloride‐free solution. Hiatt and Leggett (1974) reported that increasing Cl^‐ concentration in the solution suppressed NO^‐ ₃ uptake by the plant. Direct competition between NO^‐ ₃ and Cl^‐ on uptake by plants was also reported by DeWit et al. (1963). There is therefore a possibility that yield reduction due to increased salinity is not entirely from Cl^‐ toxicity, but may be partially due to induced deficiency of NO^‐ ₃ by the increased external Cl^‐concentration (Wallace and Berry, 1981).

Reports on the effect of H₂FO^‐ ₄ interaction with salinity are conflicting (Champagnol, 1979). Some investigators report positive and others report negative effects of increased H₂PO^‐ ₄ concentrations on plant resistance to salinity. Nieman and Clark (1976) found that decreasing H₂PO^‐ ₄ from 1 to 0.1 meq/l increased resistance of the plant to salinity.

The purpose of the work reported herein was to check the hypotheses that increasing NO^‐ ₃ and H₂PO^‐ ₄ concentrations in the nutrient solution will decrease Cl^‐ uptake and thus increase plant resistance to Cl^‐ salinity or conversely high Cl^‐ in the water requires higher NO^‐ ₃ concentration for adequate N supply as compared to low Cl^‐.