Agricultural soils as a sink to mitigate CO₂ emissions

Abstract

Abstract. Agricultural soils, having been depleted of much of their native carbon stocks, have a significant CO2 sink capacity. Global estimates of this sink capacity are in the order of 20‐30 Pg C over the next 50‐100 years. Management practices to build up soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors. In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N‐fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no‐till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration. In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In extensive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no‐till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of CO2 from biomass and soil are emitted to the atmosphere. Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region‐specific interactions between climate, soil and management resources that are lost in global level assessments. By itself, C sequestration in agricultural soils can make only modest contributions (e.g. 3‐6% of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single ‘magic bullet’ solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.

Agricultural bio-char production, renewable energy generation and farm carbon sequestration in Western Australia: Certainty, uncertainty and risk

“…Working Group III also stated the high agreement and much evidence that soil carbon sequestration is the mechanism responsible for most climate change mitigation potential (Paustian et al, 1997). The IPCC's AR4 Synthesis Report confirmed that effective carbon-price signals can mobilise environmentally effective mitigation options in the agriculture and forestry sectors, including as improved land management practices that maintain soil carbon density and for soil carbon sequestration.…”

Estoque de carbono orgânico no solo e emissões de dióxido de carbono influenciadas por sistemas de manejo no sul do Brasil

“…Sistemas de manejo que aumentem a adição de resíduos vegetais e a retenção de C no solo se constituem em alternativas importantes para aumentar a capacidade de dreno de C-CO 2 atmosférico e mitigação do aquecimento global (Amado et al, 2001;Bayer et al, 2006). Várias são as ênfases e as formas de quantificar o efeito de sistemas de manejo sobre os fluxos de C no sistema solo-planta-atmosfera citadas na literatura (Paustian et al, 1997;Janzen et al, 1998). O balanço de C no solo é dependente da relação entre as adições de C fotossintetizado pelas plantas (parte aérea e raízes) e as perdas de C para a atmosfera resultantes da oxidação microbiana do C orgânico a CO 2.…”

Redox potential (Eh) and pH as drivers of soil/plant/microorganism systems: a transdisciplinary overview pointing to integrative opportunities for agronomy

“…The type of plants cultivated and their sequence in the crop rotation influences soil Eh and pH for two reasons: (i) plants and their associated microorganisms play a crucial role in the formation and alteration of soil (Lambers et al 2009); and (ii) plant biomass production and inputs to the soil influence soil organic matter content, which buffers the Eh and pH of the bulk soil (Paustian et al 1997). In the surface horizon (0-30 cm) of an aerobic soil, Bohrerova et al (2004) measured significant soil Eh differences between cropping systems, with a higher Eh on an alfalfa/wheat rotation than on a sugar beet/barley rotation.…”