Question: What is carbon farming?
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Carbon farming is a method of farming that reduces rates of greenhouse gas emissions and/or increases capture and retention of carbon in vegetation and soils. Carbon farming is supported financially by a federal government Emission Reduction Fund, which provides incentives for these practices.
Increased carbon storage can be achieved by increasing the area of land in woodland/forest, and by increasing the amount of "soil organic carbon". There are 12 to 13million tonnes of carbon stored in Australian woodlands/forests. This includes carbon above ground, below ground, in litter, and the soil.
We'll focus at soil organic carbon here, and I'll cover forest carbon farming in a future column.
Globally there are about 550billion tonnes of carbon in terrestrial vegetation, and about 1500 to 2000 billion tonnes in the top metre of soil. Australian soils contain about 25billion tonnes in the top 0.3metres.
Increased soil carbon is highly beneficial to plant health and yield. Reduced tillage, stubble retention and other management practices such as ley cropping, and rotational cropping/grazing can improve soil carbon.
The State of the Environment Report 2016 suggests the evidence for improvements in soil carbon due to changes in land management practices is less than overwhelming.
Climate, especially temperature and rainfall, may have stronger impacts on soil carbon than land management. Warm temperatures increase decomposition rates of plant residue, making it harder to achieve high soil carbon in the tropics. Soils in arid climates are also less able to accumulate carbon.
Biochar is a charcoal-like material produced by heating organic material in the absence of oxygen. It is also produced naturally during bushfires. Biochar helps retain water and nutrients, and improve crop yield. It can also lock up carbon into a long-lived carbon pool. It is increasingly viewed as a means of carbon farming, although long-term impacts of biochar on soil properties remain unknown. Furthermore, the feedstock used to produce biochar and the temperature applied during its generation significantly influences its properties and efficacy.
Response by: Professor Derek Eamus, University of Technology Sydney
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