Compost stability, phytotoxicity and nutrient quality as influenced by carbon to nitrogen ratios of feedstock

Abstract

Effects of three C/N mixes of groundnut husk (GNH) and Wister rat litter (RL) on stability, nutrient quality and phytotoxicity of compost were tested and compared with the conventional carbon and nitrogen feedstock mix on 1:3 w/w modality respectively. The GNH and RL were respectively composted in a windrow at three proportionate levels (14.7+105.3, 39.2+80.8 and 63.7+56.3 kg) to achieve C/N nutrient ratios of 20:1, 30:1 and 40:1 respectively using the Pearson square method. A control pile containing GNH+RL (tagged conv. 1:3) applied at 30 kg GNH and 90 kg RL using the conventional 1:3 w/w modality was compared in triplicate. Data were taken on daily compost temperature, pH, EC and nutrient content of stabilized composts. Phytotoxicity was assessed by using two compost extract concentrations of 100 and 50% per compost. There were three replications laid in CRD. Data were statistically analyzed. Number of days to compost stability was significantly influenced by C/N with values increasing with decreasing C/N in the order of 59 < 69 < 74 < 77 days for 40:1, 30:1, 20:1 and conv. 1:3 respectively. Increasing C/N decreased pH (range of 7.3 – 9.0), EC (range of 1.2 – 2.7dS/m), ash (range of 44.2 – 55.5%), total macronutrient (N+P+K) (range of 3.56 – 5.15%) and calcium content (range of 3.3 – 6.5%) and increased organic C (range of 22.4 – 29.6%) of the resultant composts and GI (range of 25 – 76%) of cowpea. The 100 and 50% concentrations supported higher GI of cowpea in composts produced from lower and higher C/N respectively.