Biochar effects on nitrous oxide and methane emissions from soil

Abstract

Since the literature review by Van Zwieten et al (2009), our understanding of the infl uence of biochar on the non-CO2 greenhouse gases (GHG), nitrous oxide (N2O) and methane (CH4) has expanded signifi cantly. Nitrous oxide is a potent greenhouse gas (ca. 300 times that of CO2) and an important ozone depleting compound (Ravishankara et al, 2009). Its atmospheric concentration has increased from 270 parts per billion by volume (ppbv) in the pre-industrial era to over 324ppbv (Ussiri and Lal, 2013; IPCC 2013). Agricultural emissions (4-6Tg N2O-N yr−1) result from N fertilizer use and manure management, while emissions from natural soils (6-7Tg N2O-N yr−1) represent 56-70 per cent of all global N2O sources (Syakila and Kroeze, 2011). Methane has a radiative forcing approximately 25 times that of CO2 (Forster et al, 2007) and its concentration has more than doubled in the atmosphere since pre-industrial times to a concentration of 1803ppbv (IPCC, 2013). Soils are a major sink for CH4 and to our knowledge the lastassessment of the human impact of land-use changes and fertilizer use on global CH4 consumption was made 20 years ago (Ojima et al, 1993); the authors estimated that human activities had already reduced the global net CH4 sink capacity by 30 per cent. Since then, the rising use of mineral N fertilizer (Galloway et al, 2008), soil degradation and forest clearcutting, rising atmospheric CO2 and frequency of heat waves (Hansen et al, 2012) will further have reduced the global methanotrophic CH4 sink. Therefore, any positive contribution that biochar can provide to agricultural soils in terms of strengthening the soil CH4 sink is of global signifi cance.