Global potential for increasing biofuel crop yields/acre
March 16th, 2012 by Rachel Perlman,Article: Fargione, J. (2012). Boosting biofuel yield. Nature Climate Change 1: 445-446.
Background: One of the main concerns with biofuel production centers on land use change; if we convert natural ecosystems or food croplands to biofuel crops, we may be worsening other environmental and food security problems. There is debate over the extent to which biofuel production directly competes with the food market and increases food prices. In order to increase global biofuel production without the agricultural expansion, biofuel yields would have to increase.
Summary: Fargione explains that Johnston et al. have calculated that an extra 112.5 billion liters of ethanol and 8.5 liters of biodiesel could be produced if global yield for crops used to make biofuels increases (with crop area staying constant). They determined the potential yield gain by comparing current production levels with a scenario in which the half of the world’s farmers having below median yield increased yields to median levels. Separate median yield values were identified for each major crop used to produce ethanol and biodiesel in each climate zone. Thus, yields from locations that have similar numbers of growing degree-days and soil moisture/types (such as Indonesia and Brazil) and grow the same crop (like sugar-cane) were grouped together. The variation in yields of a given biofuel crop creates a “yield-gap” that would ideally be reduced by adjusting management practices, inputs, equipment, or the cultivar variety. For example, if Madagascar were to have its lower-yielding half of farmers produce at median yield levels, they could double sugar-cane yields.
Despite the great potential for energy crop yield increases, the means by which this can occur are not straightforward. Especially in developing countries, yields are often lower due to lack of capital, access to equipment, and education on farm management. Solutions require some combination of monetary aid, educational outreach, and investment in infrastructure and technology. However, closing the energy crop yield gap also has concerning realities – more fertilizers and irrigation will be needed, and with global food demand growing, policy-makers have to decide what proportion of resources should go toward biofuel versus food crops.
CATF take-away message: Boosting agricultural yields is essential to meet the growing demand for food, animal feed, and other plant-based products. However, the idea that increasing yield/acre of biofuel crops is always a “win-win” – i.e., because it would increase energy production while preventing detrimental land-use change – needs to be considered carefully. Before pouring resources into efforts to make higher yielding energy crops, we must make sure that the carbon footprint and energy balances of the biofuel production process (currently, as well as with the adjustments for higher yield) are acceptable to in the first place.
RESEARCH: Environmental feasibility comparison of palm seed biodiesel, Jatropha curcas biodiesel, and oil biodiesel.
July 3rd, 2009 by CATF,Article: MH Jayed et al (2009). Environmental aspects and challenges of oilseed produced biodiesel in Southeast Asia. Renewable and Sustainable Review. Vol. 13(9), pp. 2452-2462
Southeast Asia is a major producer of biodiesel from palm seed oil and from the Jatropha curcas plant. These feedstocks have environmental advantages over conventional diesels, but they also create their own environmental damages. This study compares the life cycles of palm seed biodiesel, Jatropha curcas biodiesel, and oil biodiesel to determine which is the most environmentally feasible in terms of yield rate, land use, engine emissions, and oxidation stability. Palm seed oil is found to be the most environmentally feasible feedstock in all categories except for the production of nitrous oxide, where petrol-based diesel is actually superior.
The full article can be downloaded here.
RESEARCH: Global expectations for biofuels are unreasonable
January 13th, 2009 by CATF,Article: Matt Johnston et al (2009). Resetting global expectations from agricultural biofuels. Environ. Res. Lett. 4 014004. doi: 10.1088/1748-9326/4/1/014004
Synopsis: Matt Johnston, Tracey Holloway, and Chris Kucharik of the Center for Sustainability and the Global Environment (SAGE) at the University of Wisconsin as well as Jonathan A Foley and Chad Monfreda develop a more accurate biofuel yield analysis with the intention of resetting the “global expectations surrounding agricultural biofuels to a more realistic starting point.”
Production potential for biofuels has, prior to this point, been largely based off of fuel yields per unit area of biofuel feedstock. Johnston et al explain that highly cited yield tables are derived from assigning a single value to represent the production of an entire global feedstock regardless of the conditions in which the feedstock was produced, such as “geographic location, climate, soil, type, or agricultural management regime.” Accounting for these factors can have a dramatic influence on fuel yield values.
The revised yield analysis presented in this article makes use of M3 datasets, which demonstrate patterns of actual, reported yield that account for differences in location for various biofuel feedstocks. M3 data are gathered through reporting methods at “county, state, and country levels” and are then cross-referenced to a map of global croplands. Values are converted to liters-per-hectare. Johnston et al calculated yield quartiles and distributions for each crop in each country.
The study finds that by accounting for global expansion of feedstocks, previous estimates may have overestimated potential production yields anywhere from 100-150% depending on the crop. This study serves as a starting point that allows future research to quantify the potential of biofuels as well as the impacts of biofuel feedstock production.
The full article can be downloaded here.
RESEARCH: Use of the ‘ecosystem carbon payback time’ metric implies biofuel crop expansion will not be carbon beneficial.
July 9th, 2008 by CATF,Article: Holly K. Gibbs et al (2008). Carbon payback times for crop-based biofuel expansion in the tropics: the effects of changing yield and technology. Environ. Res. Lett. 3 034001 (10pp) doi: 10.1088/1748-9326/3/3/034001
Synopsis: Researchers Holly K Gibbs, Matt Johnston, Jonathan A Foley, Tracey Holloway and David Zaks from the Center for Sustainability and the Global Environment at the University of Wisconsin as well as Chad Monfreda and Navin Ramankutty, find that “no foreseeable technologies can make tropical deforestation for biofuel crop expansion a carbon beneficial enterprise.”
Gibbs et al project a trend toward deforestation of tropical ecosystems in response to biofuel mandates as well as demand for food and feed. These tropical ecosystems contain 340 billion tonnes of carbon, noted as 40 times the value for human induced fossil fuel emissions each year.
Gibbs and the coauthors utilize the ‘ecosystem carbon payback time’ (ECPT) metric highlighted in Fargione et al (2008). ECPT is defined, in the context of biofuels, as the amount of time (in years) that it will take for the emissions savings from biofuels to make up for the flow of carbon from the ecosystem to the atmosphere due to deforestation for the growth of feedstocks. The necessary biomass carbon stocks were estimated based on IPCC Good Practice Guidance Tier-1 methods for tropical ecosystems as well as grasslands and savanna. Researchers used a map of croplands by Monfreda et al (2008) to determine crop areas and yields. In order to allow for scenarios of future improvement in crop yield, researchers calculated the equation using only the top 10% yield for each crop. The analysis ignores emissions from distribution, production and manufacturing processes associated with biofuels.
Gibbs et al find that replacing productive lands with low-yield crops results in the longest payback period and replacing marginal lands with high yield crops results in the shortest payback period. Findings are consistent for nontraditional forms of fossil energy such as tar sands and heavy oils that have higher ‘upstream emissions,’ taking decades to centuries of payback for lost carbon from tropical ecosystems. The article confirms findings by Fargione et al (2008), which concluded that, “clearing of tropical forests and grasslands to produce biofuels leads to long-term carbon debt while only converting degraded lands will provide carbon savings.” Gibbs and the coauthors suggest the importance of keeping shorter payback periods for marginal lands in perspective, as marginal lands require more intensive agricultural practices.
The article concludes that, “the carbon payback times for clearing tropical forests are unacceptably large in the context of any carbon mitigation efforts” and that “no foreseeable technologies can make tropical deforestation for biofuel crop expansion a carbon beneficial enterprise.”
The full article can be downloaded here.
