March 2012 C&CI • Climate Change • 35
Possible means of mitigating the increase in carbon footprint from increased fertilization and productivity include:
■ Applications of organic matter, com- post or manure, which contribute to emissions of nitrous oxide but can also increase the carbon content of the top soil ameliorating the emissions
■ Application of pruning material from shade regulation of the trees and coffee can also contribute to nitrous oxide emissions and the carbon footprint, but have a lower emission factor and also contribute to increasing carbon content of the top soil.
■ Both organic inputs and pruning materi- als contribute to N2O emissions from the soil but they generally do not have emis- sions related to the manufacturing of the product – as with chemical fertilizer – thus the carbon footprint per kg of organic nitro- gen applied is lower. However, they may also be less effective in increasing produc- tivity, which may offset the lower GHG emissions from their application in terms of carbon footprint per kg of coffee produced.
On-farm and across
the value chain What, then, is the potential for carbon sequestration on-farm to offset the emis- sions from the whole chain? And what are the conditions that may enable that to happen?
If we take the only published full coffee carbon footprint (PCF 2008) it indicates that about 55 per cent of the carbon foot- print of a cup of coffee is from on-farm
Shaded coffee systems that already have large carbon stocks are a different scenario. Although established shaded coffee systems can hold substantial stocks of carbon there is no data to enable us to estimate whether these systems can continue to sequester carbon
emissions. This means that carbon sequestration on-farm must be approximately twice as high as emissions on-farm if the carbon footprint from the rest of the value chain is to be inset. The potential to generate the carbon to be inset depends on whether the coffee planta- tion, or at least the shade trees, are already established or newly planted.
Newly planted shaded coffee systems, or coffee in which shade has been planted where the coffee used to be grown in full sun, can fix sufficient car- bon to offset agronomic emis- sions during a period of ten years at least. After this, at some point, carbon sequestra- tion from the growth of the trees will fall off and the situa- tion becomes similar to estab- lished coffee systems.
Full sun
If we take our three experimental systems presented earlier in table 2, the full sun production system doesn’t cover its own emissions and the legume shad- ed system was accruing 50 per cent more carbon than it was emitting over a nine year period. So there is some potential to off- set emissions but not enough for the whole value chain.
Timber shade
Finally, the timber-shaded value chain sequesters four times as much carbon as is emitted, which would indicate that this system could offset the carbon emissions of the rest of the supply chain (that is, it can ‘inset’ the carbon emissions in the value chain). This final scenario is a very partic- ular one – of planting new timber trees on a deforested site with coffee, but a similar scenario could be expected by planting free growing trees in un-shaded coffee. Shaded coffee systems that already have large carbon stocks are a different scenario. Although established shaded coffee systems can hold substantial stocks of carbon there is no data to enable us to estimate whether these sys- tems can continue to sequester carbon.
Figure 2 Relationship between carbon footprint and N inputs from fertilizer and prunings in organic and conventional farms in Costa Rica and Nicaragua (Noponen 2012)
The likelihood is that it will depend on the dynamic of tree shade regulation, har- vesting, mortality, and planting as to whether carbon stocks continue to increase. In general, it can be said that allowing trees free growth (as opposed to regulating shade) will increase carbon stocks, but this may also affect productivi- ty. Estimating carbon sequestration in established coffee will require measure- ments of changes in stocks every 3-5 years to determine whether the system represents a carbon sink overall. Nevertheless, if it is recognised that there is an economic cost in terms of loss of potential productivity from not reducing shade and intensifying production then a
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