Cropland management techniques for carbon storage


Courtesy of European Commission, Environment DG

The Kyoto protocol of 1997 recognises cropland management as a carbon sequestration strategy which may help to mitigate climate change. Under the protocol, ratified by the EU in 2002, member states are obliged to reduce the sum of their emissions of greenhouse gases to 5 per cent below their 1990 levels. Appropriate cropland management may help member countries meet the overall EU emissions targets.

Climate change induced changes in temperature and rainfall will have an impact on the natural cycling of soil organic carbon by directly affecting environmental biochemistry and possibly indirectly by changing agricultural practice. A new study has modelled the interaction of several cropland management practices with a number of climate change projections to assess their potential as carbon sinks. The research has compared three cropland management practices- reduced tillage, manure fertilisation or conversion to grassland - against a ‘business as usual’ scenario based on the existing crop rotation and fertilisation practice at an experimental farm in north-east Italy, which has been carrying out a long-term trial since 1966. Climate simulations were carried out using four climate models, which include four different IPCC greenhouse gas emissions scenarios.

The differences in predicted carbon content of the top layer of the soil under the different soil management practices were calculated for 2012 (the end of the first commitment period under the Kyoto protocol) and 2080. The model simulations matched well the changes from 1966 to the present day.

Climate change initially increases carbon input to the soil by increasing biomass productivity at the surface, but soil management was also shown to have an influence on soil carbon. Under ‘business as usual’ all climate scenarios predicted an increase in soil organic carbon (SOC) to 2012. Whilst manure fertilisation accumulated more SOC up to 2012, in the long term reduced tillage eventually became more efficient, because it slows down the rate of SOC decomposition. Conversion to grassland was up to 3 times more efficient as a carbon sink than any other strategy under all model combinations, over the short- and long-term.

The model suggests that summer crops like maize or soybean may be affected more negatively than winter crops like wheat, whose predicted yields increased linearly as a consequence of increased atmospheric CO2. However, different climate change scenarios produced markedly different outcomes, and such climatic uncertainty makes long-term management planning difficult. Changes in agricultural technology such as genetic modification, or responsive variation in planting, irrigation and harvesting regimes will also affect the efficiency of future cropland management strategies.

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