Biochar effects on methane emissions from soils: A meta-analysis

Methane (CH4) emissions have increased by more than 150% since 1750, with agriculture being the major source. Further increases are predicted as permafrost regions start thawing, and rice and ruminant animal production expand. Biochar is posited to increase crop productivity while mitigating climate change by sequestering carbon in soils and by influencing greenhouse gas fluxes. There is a growing understanding of biochar effects on carbon dioxide and nitrous oxide fluxes from soil. However, little is known regarding the effects on net methane exchange, with single studies often reporting contradictory results. Here we aim to reconcile the disparate effects of biochar application to soil in agricultural systems on CH4 fluxes into a single interpretive framework by quantitative meta-analysis.\ud \ud This study shows that biochar has the potential to mitigate CH4 emissions from soils, particularly from flooded (i.e. paddy) fields (Hedge's d = −0.87) and/or acidic soils (Hedge's d = −1.56) where periods of flooding are part of the management regime. Conversely, addition of biochar to soils that do not have periods of flooding (Hedge's d = 0.65), in particular when neutral or alkaline (Hedge's d = 1.17 and 0.44, respectively), may have the potential to decrease the CH4 sink strength of those soils. Global methane fluxes are net positive as rice cultivation is a much larger source of CH4 than the sink contribution of upland soils. Therefore, this meta-study reveals that biochar use may have the potential to reduce atmospheric CH4 emissions from agricultural flooded soils on a global scale

Soil Water Repellency Dynamics in Pine and Eucalypt Plantations in Portugal – A High-resolution Time Series

During the 20th century, afforestation resulted in plantations of Pine and Eucalypt becoming the main crops in north-central Portugal with associated and well-known soil water repellency (SWR). The aim of this study was to improve the insights in the temporal dynamics and abrupt transitions in water repellency of the topsoil and the mechanism that determine the behaviour of SWR. Topsoil water repellency was monitored in the Caramulo Mountains (north-central Portugal) between July 2011 and June 2012. The intensity of SWR was measured in situ at soil depths of 0, 2.5 and 7.5 cm using the ‘molarity of an ethanol droplet’ test. Volumetric soil moisture content was monitored in situ using a Decagon ECH2O EC-5 probe. SWR behaviour broadly followed five alternating dry and wet periods during the 12-month period, with more pronounced differences in the Pine site than in the Eucalypt site. SWR under Eucalypt was substantially more temporally dynamic than under Pine, with double the number of moderate and large SWR changes at the 7.5 cm depth. Soil moisture content and antecedent rainfall were better correlated to SWR under Pine than under Eucalypt, although in both cases insufficient to predict the temporal variations