Nitrogen concentration, ammonium/nitrate ratio and NaCl interaction in vegetative and reproductive growth of peanuts

Peanuts (Arachis hypogaea L. cv. Shulamit) grown with NO₃⁻ and saline water in hydroponics responded positively to addition of nitrogen (N) in their vegetative growth, but not in desert dune sand. In order to clarify these conflicting results, peanut plants were grown in a greenhouse pot experiment with fine calcareous sand. The nutrient solution contained 0 or 50 mM NaCl and 2 or 6 mM N in the form of Ca(NO₃)₂, NH₄NO₃ or (NH₄)₂SO₄. Three replicates were harvested after 48 days (beginning of reproductive stage) and three after 109 days (pod filling). In addition, gynophores were treated with 0, 50, 100, 150 or 200 mM NaCl outside the growth pot to check their sensitivity to salt. Shoot dry weight became greater with increasing NH₄⁺/NO₃⁻ ratio. Increasing the N concentration from 2 to 6 mM did not change shoot dry weight of the NH₄NO₃ or NH₄⁺‐fed plants, but caused a reduction in shoot dry weight of NO₃⁻‐fed plants. Shoot dry weight was not affected by increasing the NaCl concentration to 50 mM. Salt caused an increase in the number of gynophores per plant and a reduction of the mean pod weight. A NaCl concentration of 100 mM and above reduced gynophore vitality. It is concluded that the salt sensitivity of peanut plants resides mainly in the sensitivity of the reproductive organs.