Nitrogen fertilization under saline conditions in tomato and cucumber plants

Abstract

Tomato (Lycopersicon esculentum, Mill.) and cucumber (Cucumis sativus, L.) seedlings were grown in a growth chamber in 4 litre containers filled with nutrient solutions. Four experiments were conducted with four NaCl levels factorially combined with four N levels. The concentrations of NaCl were 4, 25, 50, and 100 mmol l⁻¹ and 4, 16, 32, and 64 mmol l⁻¹ in the tomato and cucumber experiments respectively. The N levels in allexperiments were 2, 6, 10 and 15 mmol l⁻¹ added as NO₃⁻ or as NH₄⁺ + NO₃⁻ (2:1). Salinity had a statistically significant negative effect on all responses considered, although the effect was N source-dependent. Addition of N enhanced development of shoot and root dry weights of both species. The optimum N concentration in the nutrient solution varied between 6 and 10 mmol l⁻¹, although the most appropriate N fertilizer varied with species. Leaf Cl⁻ concentration decreased in both species when NO₃⁻ was used as the N source, whereas it increased in the comparative tissues of plants fed with NH₄⁺ + NO₃⁻. The effect of treatments on the other nutrients show effects of excess of NaCl, as the form of N source interferes with the uptake of essential nutrients which may cause nutritional disorders.