The role of chemical amendments on modulating ammonia loss and quality parameters of co‑composts from waste cocoa pods


Department of Agriculture, The PNG University of Technology, Lae, Papua New Guinea


Purpose Nitrogen loss as ammonia (NH3) in a waste cocoa pod co-composting process was determined following the addition of three potential chemical amendments that could lower NH3 loss. Further, amended compost products were assessed for quality and possible phytotoxicity in a pot experiment. Methods Pod borer damaged cocoa pods were co-composted in lab-scale vessels under ambient conditions with double superphosphate, phosphoric acid, and gypsum at 2%, 5% and 1% of fresh weight, respectively. NH3 emitted during composting was trapped in standard H2SO4 and determined titrimetrically. Composting mixtures were sampled on days 0, 7, 56 and 90 to monitor pH, total C, total N, and C:N ratio. Mature co-composts were incorporated to the soil at 20 t ha−1 and growth response of Chinese cabbage plants (Brassica rapa chinensis) assessed for the phytotoxicity. Results The chemical amendments were inefective (p>0.05) in preventing loss of NH3 but the quality of composting mixtures were signifcantly (p