The study of humification process of compost using humic acid and its functional groups

Compost derived from mix manures, shopped Leucaena leucocephala de Wit, bran of rice, molace, fish fermented juice were studied their humification process by using humic acid quantity and its functional groups, which were phenolic and carboxylic groups. Samples were collected for all analysis at day 0, 7, 14, 21, 28, 35, 49, 63, 77, 91, 105, and 119. The results showed that the maturity of compost could be divided into 4 steps - the initial phase (day 0), thermophilic phase (day 1-34), end of active phase (day 35), and mature compost (36 days up). After 35 days of mixing, the highest amounts of humic acid, 280.1 mg/g occurred and was higher than the others 4.7-19.9 folds. The relationship of the amounts of phenolic acid during the period of mixing significantly correlated with the total acidity and showed the highest amounts at day 35 as well (r = 0.98; p<;0.01) while the amounts of carboxylic acid were not (p>0.01). Pearson correlation coefficients among the four major elements of humic acid: carbon (C), nitrogen (N), oxygen (O) and hydrogen (H) showed that the amounts of O significantly negatively correlated with C and H while C and H were significantly positively correlated to each other (r<;0.01). This also supported the appearance of phenolic-OH which contained high C and H and were mostly found in varieties of humic acids while carboxylic group having high O usually was found less. The highest amount of phenolic-OH was also at day 35. Therefore, both humic acid and its functional groups could be applied to estimate the humification process of the compost and helped to select the appropriate day to use compost as fertilizer.