Effect of nitrogen rates on growth and quality of water spinach (Ipomea aquatica)

Aims: The study was conducted to investigate the impact of nitrogen fertilization on growth, leaf gas exchange and bio-metabolite accumulation in Ipomea aquatica. Treatment and Experimental Design: Ipomea aquatica plants were exposed to four different rates of nitrogen (0, 30, 60 and 90 N kg/ha) using Urea (46% N) as a nitrogen source. The experiment was laid out in Complete Randomize Design (CRD). Place and Duration of Study: Department of Biology, Faculty of Science, Universiti Putra Malaysia between September to November 2016. Methodology: Four nitrogen rates were applied (0, 30, 60 and 90 N Kg/ha) using Urea as a nitrogen source. The growth data collections were conducted once a week after the application of the treatments for the plant growth parameters. The total chlorophyll content in the leaves was measured using a Soil Plant Analytical Device (SPAD-502) chlorophyll meter. The leaf gas exchange was determined using a LI-6400XT portable photosynthesis system. Total phenolics and flavonoid were determined using Folin-Ciocalteu reagent. Results: It was found that the highest measurements of growth parameters namely plant height, leaf numbers, branches numbers, total biomass and chlorophyll content were observed at 90 kg N/ha and the lowest at 0 kg N/ha. As for the leaf gas exchange, the positive effect of nitrogen fertilization on kangkung was shown by the increased in photosynthesis rate (A) and stomatal conductance (gs) where the highest measurement recorded at 90 kg N/ha, and the lowest at 0 kg N/ha. However, the water use efficiency (WUE) decreased as the nitrogen rates increased. At lower rates of nitrogen fertilization (30 kg N/ha) produced the highest production of secondary metabolites, where the total phenolics and flavonoids production were enhanced compared to other nitrogen treatments. Conclusion: In conclusion, as the nitrogen rates increased, the growth and leaf gas exchange properties was enhanced however the production of secondary metabolites was decreased in I. aquatica.

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