Effects of humic acid on vegetative growth, yield, oxalic acid and betacyanin content of red amaranth (Amaranthus tricolor L.)

Abstract

Humic acid is biostimulan that has a negative charge and it is able to bind cations that are important in the process of plant growth. Red amaranth (Amaranthus tricolor L.) is one of vegetables that contains betacyanin which is a good source of antioxidants. However, the stem and leaves of red amaranth also contains oxalate which could inhibits calcium absorption in human's body. This study was aimed to evaluated the effect of humic acid on vegetative growth, yield, oxalic acid and betacyanin content of red amaranth (Amaranthus tricolor L.). Red amaranth seeds were germinated in a polybag containing top soil as growth media. Seedling were selected and humic acid were applied through foliage spray or soil surface when plants were at 2 weeks old. The concentration variation of humic acid were 0 mg/L, 5 mg/L, 20 mg/L or 35 mg/L and there were 5 replicates for each treatment. Vegetative growth observed were plant height and leaf number, yield observed were fresh and dry weight of shoot and root. Oxalic acid content was determined by permanganometric titration method, and the density of Ca-oxalate crystal was observed from stem cut preparate made by free-hand section technique. Betacyanin content was determined by HPLC (High Performance Liquid Chromatography), and chlorophyll content was determined by spectrophometric method. Data were analyzed by One Way ANOVA (Analysis of Variance), followed by Duncan Multiple Range Test with 95% confidence level. Results showed that humic acid of 20 mg/L applied through the leaves significantly increase plant height, leaf number, the fresh and dry weight of shoot and betacyanin content. Humic acid of 20 mg/L that was applied through the soil surface also significantly increased leaf number, both fresh and dry weight of shoot and root but reduced oxalate content. From this study it can be concluded that humic acid of 20 mg/L applied either through foliage spay or soil surface increased plant height, yield and betacyanin content but it reduce doxalate content of red amaranth.