Sustainability of biochar amendment in a tropical paddy soil

Abstract

Biochar use as a soil amendment has attracted increased attention from researchers worldwide but its effects on soil properties, nutrients and greenhouse gas emissions remain scanty especially for tropical paddy soils. Biochar amendment increased initial total P from 500.11 in soil (S) to 978.90 µg/g of soil in soil amended with biochar (SB) but significantly reduced mean DOC. Biochar, however, had no effect on total nitrogen, total organic carbon, TON, organic–N and ammoniacal N. The initial soil pH was raised from 3.96 in S to 4.84 in SB by biochar amendment. It reduced CO2 emission, had no significant effect (P≤0.05) on N2O emissions but increased CH4 emissions, although the levels of CH4 were very low compared to the other greenhouse gases hence the high CO2/CH4 ratios. In addition, when co-applied with P, it suppressed the stimulating effect of P on production of greenhouse gases. Significant positive correlations were observed between CO2 and N2O as well as N2O and CO2 in SP. pH showed significant positive correlations with CH4 in S and SP, organic–N in S, SP and SPB but negatively correlated to CO2 in SPB as well as TON in SB. S and SP registered a significant negative correlation between ammoniacal–N and CH4. DOC positively correlated to TON and ammoniacal N but negatively correlated to organic-N in SP and SB. Total P positively correlated to DOC in SB, ammoniacal N in SP and SPB and TON in S. It however, negatively correlated to CH4 in SP and N2O in SPB. It is therefore a suitable additive for sustainable agriculture since it enhances soil fertility and minimizes greenhouse gas emissions, especially when combined with P fertilizer.