Biochar and biochar-compost as soil amendments: Effects on peanut yield, soil properties and greenhouse gas emissions in tropical North Queensland, Australia

This study investigated the effects of biochar and compost, applied individually or together, on soil fertility, peanut yield and greenhouse gas (GHG) emissions on a Ferralsol in north Queensland, Australia. The treatments were (1) inorganic fertilizer only (F) as a control; (2) 10 t ha−1 biochar + F (B + F); (3) 25 t compost + F (Com + F) ha−1; (4) 2.5 t B ha−1 + 25 t Com ha−1 mixed on site + F; and (5) 25 t ha−1 co-composted biochar-compost + F (COMBI + F). Application of B and COMBI increased seed yield by 23% and 24%, respectively. Biochar, compost and their mixtures significantly improved plant nutrient availability and use, which appeared critical in improving peanut performance. Soil organic carbon (SOC) increased from 0.93% (F only) to 1.25% (B amended), soil water content (SWC) from 18% (F only) to over 23% (B amended) and CEC from 8.9 cmol(+)/kg (F only) to over 10.3 cmol(+)/kg (organic amended). Peanut yield was significantly positively correlated with leaf chlorophyll content, nodulation number (NN), leaf nutrient concentration, SOC and SWC for the organic amendments. Fluxes of CO2 were highest for the F treatment and lowest for the COMBI treatment, whereas N2O flux was highest for the F treatment and all organic amended plots reduced N2O flux relative to the control. Principal component analysis indicates that 24 out of 30 characters in the first principal component (PRIN1) individually contributed substantial effects to the total variation between the treatments. Our study concludes that applications of B, Com, B + Com or COMBI have strong potential to, over time, improve SOC, SWC, soil nutrient status, peanut yield and abate GHG fluxes on tropical Ferralsols.