Wednesday, October 9, 2013

Bioenergy can work, if it is done right

Jesko Zimmerman
There isn’t much you can tell plant science researcher Jesko Zimmerman about the biomass crop Miscanthus or elephant grass.  It is widely grown throughout the EU as a commercial energy crop, which can be used for combined heat and power generation or converted into biofuel such as ethanol.  However, according to Jesko, bioenergy crops put us into somewhat of a dilemma, or a trilemma as David Tilman and colleagues put it in their noteworthy 2009  paper in the journal Science, ‘Beneficial biofuels -the food, energy, and environment trilemma’. The interesting conclusion of that paper being that bioenergy can work, if it is done right.

Miscanthus x giganteus (Image: Pat Smitz) 
Jesko’s research is exactly about that: how to do it right. His research focusses on Miscanthus x giganteus, a perennial grass originally from south-east Asia, but with the potential to produce high biomass yields even in our cooler European climates. The crop has been and still is heavily subsidised by the government and is becoming more prevalent in the Irish landscape. Although Miscanthus is highly adaptable to European climates, Ireland is at the geographical margin of where the is economically viable. Therefore it is important for farmers to produce the maximum possible yield per hectare. However, while surveying Miscanthus fields all over south-east Ireland he has  discovered lots of open patches within fields where the plants just do not grow.

This raised three questions that Jesko is very interested to finding answers to: (i) Why are they not growing in these areas, (ii) how much yield is being lost, and (iii) how is the economic feasibility of growing Miscanthus affected?

As no yield data was available for these fields, we had to measure the amount of cropped area (and therefore yield) lost due to patchiness using aerial photography, which showed an average reduction in biomass yield of 13.7%.  The economic loss was calculated using life-cycle assessment tools to compare the gross margin for each field if the full potential yield is realised and if yield loss due to patchiness is taken into account. The results showed that farmer’s gross margins were reduced by up to 35 %. The question what caused the patches has not been directly answered. However, the aerial images do give some indications. Miscanthus rhizomes are directly planted into the soil and parallel lines of linear patches indicate problems while planting the crop due to jamming in the mechanical planter, which has been confirmed by farmers. Single large patches indicate localised issues such as areas of water logging while widely spread small patches appear to  originate from planting rhizomes that did not survive storage. Generally it could be shown that patchiness may not be an immediate problem for farmers, but that addressing the issue could have significant economic benefits. While the cause of patchiness was not directly investigated, it can be said that taking more care when planting should reduce the crop patchiness. More details of this can be found in Jesko’s recent paper in Global Change Biology Bioenergy. ‘Assessing the impact of within crop heterogeneity (‘patchiness’) in young Miscanthus × giganteus fields on economic feasibility and soil carbon sequestration’.


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