Responses of cucumber plant to NH 4+ and NO 3− nutrition: The relative addition rate technique vs. cultivation at constant nitrogen concentration

Abstract

Different N sources (NO 3 −, NH 4 +, or NH 4NO 3) at different relative addition rates (RAR) were supplied to cucumber ( Cucumis sativus L.), a species sensitive to NH 4 + toxicity. For comparison, cucumber plants were also grown at constant concentrations of 1 and 5 mM NH 4 + or 5 mM NO 3 −. The fresh weight of NH 4 +-fed plants at RAR 0.15 and RAR 0.25 day −1 was similar to that of NO 3 −-fed plants, while at RAR 0.35 or RAR 0.45 day −1 growth reduction occurred. When available as a constant concentration, NH 4 + decreased plant growth at 5 mM. It is concluded that at low rates of N supply the relative addition rate technique can be used for growing cucumber plants with NH 4 + as sole N source without deleterious effects.