Abstract:
This research investigates the dynamic of nitrogen species during composting of mixed bovine and porcine manure compost. The samples were collected for 4 months at days 0, 3, 7, 14, 21, 28, 35, 42, 49, 63, 77, 91, and 119. The maturation of compost was divided after temperature into 3 stages: the initial stage (at day 0), the thermophilic stage (during day1-13), and the mature stage (since day 14). The most proportion of nitrogen was organic nitrogen (Org-N) with in the range of 88.26-96.54% while the available nitrogen (AN) consisting of ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3- -N) was found with in the range of 3.4611.74%. The amounts of Org-N increased corresponding with time (r=0.577, p<0.01) together with NO3--N (r=0.899, p<0.01) which in responding with the increasing amounts of total nitrogen (TN) (r=0.655, p<0.01). This explained the decomposition process releasing more forms of nitrogen and increasing the nitrogen contents. The ammonification process prevailed during the thermophilic phases releasing more NH4+-N contents and gradually decreased when approaching the mature stage via the nitrification process. Therefore, the amounts of NO3--N was in the opposite direction of the amounts of NH4+-N (r=-0.945, p<0.01). However, the electrical conductivity (EC) increased upon the composting process as more nutrient ions were discharged. The ECs were excessing the standard of Thai compost quality since day 77. The nitrification index (NH4+-N/ NO3- -N) indicated that after day 28 the compost was appropriate to use. Nevertheless, the best utilizing of this compost should be during day 42-63 in which the TN, Org-N, and NO3--N were in the higher amounts and other parameters were met the standard of Thai compost criteria.