Mineral nutrition of chickpea plants supplied with NO3 or NH4 N

Chickpea plants (Cicer arietinum L cv. ILC 195) were grown for 24 days in water culture under two regimes of nitrogen nutrition (NO₃ or NH₄‐N) with or without Fe. For plants fed with NO₃‐N, Fe stress severely depressed fresh weight accumulation and chlorotic symptoms of Fe‐deficiency developed rapidly. Little difference in growth occurred in the NH₄‐fed plants, whether or not Fe was withheld, with no visual evidence of Fe‐deficiency indicating a beneficial effect of NH₄ in depressing the symptoms of Fe chlorosis. Typical pH changes were measured in the nutrient solution of the control plants in relation to nitrogen supply, increasing with NO₃ and decreasing with NH₄‐nutrition. With both forms of nitrogen, plants acidified the nutrient solution in response to Fe‐stress. Under NH4‐nutrition, acidification was enhanced by withholding Fe. In the NO₃‐fed plants the uptake of all nutrients was reduced by the stress but proportionally NO³‐ and K⁺ were most affected. Total anion uptake was depressed more than that of cation uptake. For the NH₄‐fed plants withholding Fe resulted in an increased uptake of all ions except NH₄ ⁺ which was depressed. Regardless of the form of N‐supply, when Fe was withheld from the nutrient solution the net H⁺ efflux calculated from the (C‐A) uptake values was closely balanced by the OH” added to the nutrient solution to compensate for the pH changes. Evidence of accumulation of organic acids in the Fe‐stressed plants was found, especially in the NO₃‐fed plants, indicating a role for these internally produced anion charges in balancing cation charge in relation to the depression of NO₃ ^‐ uptake associated with Fe‐stress.