Do NH4:NO3 ratio and harvest time affect celery (Apium graveolens) productivity and product quality?

Abstract

Abstract Due to the remarkable health benefits of celery (Apium graveolens), its consumption has increased over time. A partial substitution of NO3 − with NH4 + is recommended to limit the accumulation of NO3 − in leafy vegetables. Hence, a factorial experiment with two factors, consisting of six treatments as combinations of three NH4:NO3 ratios (0:100, 20:80 and 40:60) in nutrient solutions and two harvesting times (in the morning and in the evening), was conducted on celery plants in a soilless culture system. The results showed that 100% NO3 as a sole N source significantly increased plant height, leaf number, chlorophyll, fresh weight, N, K, Ca, Mg, Fe, Mn, Zn, protein, dietary fibre, soluble sugars, nitrate, vitamin C, α-carotene, β-carotene and lutein of celery plants compared to either 80 or 60% NO3. However, this increase was not significant compared to 20% NH4:80% NO3 in terms of leaf number, fresh yield, N, Mg, Mn, protein, soluble sugars, vitamin C and α-carotene. Harvesting in the evening significantly increased K, Mg, Fe, soluble sugars, α-carotene and β-carotene, and lowered the nitrate level in celery plants. In conclusion, partial replacement of 20% NO3-N with 20% NH4-N and evening harvesting are recommended for a greater fresh yield, higher quality, and lower nitrate level.