Washington, February 25 : A new study suggests that organic fertilizers-like those resulting from composting-may increase the amount of carbon stored in agricultural land, and thereby make a significant contribution to the reduction of greenhouse gas emissions.
In a special issue of Waste Management and Research, a journal from the international publisher SAGE, the study report says that the Intergovernmental Panel on Climate Change and the European Commission consider carbon sequestration in soil to be one of the possible measures through which greenhouse gas emissions can be mitigated.
Its authors-Enzo Favoino and Dominic Hogg-write that according to estimates, about 20 per cent of the surface of agricultural land in the EU may be used as a sink for carbon. This approach may constitute about 8.6 per cent of the total EU emission-reduction objective, they add.
"An increase of just 0.15pc in organic carbon in arable soils in a country like Italy would effectively imply the sequestration of the same amount of carbon within soil that is currently released into the atmosphere in a period of one year through the use of fossil fuels," write the authors of the paper.
"Furthermore, increasing organic matter in soils may cause other greenhouse gas-saving effects, such as improved workability of soils, better water retention, less production and use of mineral fertilizers and pesticides, and reduced release of nitrous oxide," they add.
It is, however, believed that capitalising on this potential climate-change mitigation measure is not a simple task. The issue is complicated by the fact that industrial farming techniques are actually depleting carbon from soil, and thus reducing its capacity to act as a carbon sink.
But Hogg and Favoino insist that this loss of carbon sink capacity is not permanent. They strongly believe that composting can contribute in a positive way to the twin objectives of restoring soil quality and sequestering carbon in soils.
According to them, applications of organic matter in the form of organic fertilizers can either lead to a build-up of soil organic carbon over time or a reduction in the rate at which organic matter is depleted from soils.
The authors say that the overall quantity of organic matter in soils will be higher than using no organic fertilizer in either case.
"What organic fertilizers can do is reverse the decline in soil organic matter that has occurred in relatively recent decades by contributing to the build-up in the stable organic fraction in soils, and having the effect, in any given year, of ensuring that more carbon is held within the soil," they say.
To take account of the positive and negative dynamics of carbon storage in soil, Favoino and Hogg have modelled the dynamics of compost application and build-up balancing this with mineralization and loss through tillage.
Their results suggest that soils where manure was added have soil organic carbon levels 1.34 per cent higher than un-amended soils, and 1.13 per cent higher than soils amended with chemical fertilizers, over a 50-year period.
"This is clearly significant given the evaluations reported above regarding carbon being lost from soils, and the increasing amount of carbon dioxide in the atmosphere," they say.