Effects of replacing of nitrate with urea or chloride on the growth and nitrate accumulation in pak-choi in the hydroponics

Abstract

The effect of replacing nitrate with urea or chloride on growth of pak-choi, nitrate accumulation and mineral nutrient contents were studied. Plant growth was promoted by 25% and 50% nitrate replaced with urea, but 100% substitution of nitrate with urea was inhibitory. Nitrate accumulation decreased with the decrease of the NO3-N/urea-N ratios. The contents of K, Ca, Mg were decreased by high urea-N/NO3-N rations, especially in the root. Plant growth was decreased by 50% replacement of nitrate by chloride in the nutrient solution containing 7.5 mM NO-3 and 2.5 mM urea-N, and largely reduced by replacing all the nitrate with urea. Nitrate accumulation was considerably reduced by replacing nitrate with chloride, and the chloride contents were greatly increased. The contents of K, Ca, Mg, were decreased by the complete substitution of chloride for nitrate.