Gaseous carbon and nitrogen losses during composting of carbonized and un‐carbonized agricultural residues in northern Ghana

Abstract

Adding biochar to nutrient rich organic matter during composting reportedly reduces nitrogen (N) volatilization and carbonization of feedstock stabilized organic carbon (C). We studied the effects of biochar, produced from agricultural residue as compost additives, on CO2, N2O, and NH3 fluxes in northern Ghana. Three biochar types [from corn cobs (cCC), rice husks (cRH), and wood (cWO)] and their uncharred feedstocks (CC, RH, and WO), were co‐composted with poultry manure (15 vol.‐%) and rice straw (60 vol.‐%) in randomly allocated 1 m3 compost bins. Emissions were measured using a closed chamber system composed of a photo‐acoustic infrared gas analyser (INNOVA 1312‐5). Biochar amended composts showed higher CO2‐C emission rates during the initial composting phase. Maximum CO2‐C flux rates during the first week reached 15 g CO2‐C m−2 h−1 in cRH and 12 g CO2‐C m−2 h−1 for RH, while those from cCC were 19 g CO2‐C m−2 h−1 and from CC 14 g CO2‐C m−2 h−1. Respiration significantly dropped during the last week of composting and lower rates recorded with carbonized compared with the un‐carbonized feedstocks. Total CO2‐C losses were 12 kg m−2 34 d−1 for RH and 9 kg m−2 34 d−1 for cRH, resulting in a 29% reduction of CO2‐C. Emissions were 9 and 10 kg CO2‐C m−2 34 d−1 for cCC and CC, while cWO and WO emitted 7 and 8 kg CO2‐C m−2 34 d−1, respectively. Volatilization of NH3‐N was significantly lower in compost containing cWO (89 g N m−2 34 d−1) compared to WO (166 g N m−2 34 d−1), while N2O‐N emissions were lower in compost mixtures containing cRH (27%), cCC (7%), and cWO (16%) compared with their un‐carbonized feedstock.