Poster-How to Build Soil Carbon with Sub-tropical Pastures on Marginal Crop Lands for Climate Change Adaptation

Media type: 
David Lloyd
J.F. Clewett
D. A. George
Australian Institute of Agricultural Science and Technology
Agroclim Australia
NCCARF, Griffith University

This poster considers how to build up carbon in the soil on marginal crop lands in the sub-tropics, enabling greater infiltration and retention of rainfall as an adaptation to expected climate impacts of increased temperature and more uncertain rainfall. 

Well-managed grass pastures build soil carbon slowly through microbial processes. Legume-based pastures that fix N and drive higher biomass production of associated grasses, drive a more rapid carbon accretion. In legume swards, organic carbon accretion has been in the order of 12-15% of the biomass produced/annum. Enhanced soil carbon is beneficial because it enables greater infiltration and retention of rainfall and this compensates for expected increases in temperature and more uncertain rainfall.

Marginal cropping lands in the sub-tropics are usually in poor condition with soils having reduced organic matter, low N fertility, and poor structure. Production is constrained by limited infiltration, water holding capacity, and associated with higher erodibility. They are more vulnerable to the expected impacts of climate change viz. increased aridity and/or increased rainfall intensity.

Establishment of pastures on these lands is often desirable but difficult because of the significant challenges from the climatically variable environment and the relative short-term profitability of grain growing versus grazing in good seasons. Review of progress over the past 50 years regarding appropriate methods for transforming marginal cropping lands to permanent or ley pastures reveals: (a) significant advances in the release of productive, well adapted grass and legume cultivars, (b) improved land preparation and sowing methods to achieve successful establishment, (c) improved risk management practices through increased knowledge of weather systems and climatic phenomena such as El Niño and La Niña, (d) variable rates of soil carbon accretion between 450-650 kg/ha/yr until reaching equilibrium, depending on season.

We recommend that incentives are needed with accompanying education programs that include longer-term economic analysis that lead to: (a) continued accelerating adoption of improved pastures to build soil carbon, (b) developing ‘best-management’ practice manuals on managing climate risk, and (c) measuring carbon fluxes in grazed grass/legume pastures to demonstrate how to maximise soil carbon accretion.