Study Suggests That Use of Land-Efficient Animal Feed Technologies and Double Cropping Could Reconcile Large-Scale Biofuel Production With Food Production
Large scale biofuel production can be successfully reconciled with food production through the use of land-efficient animal feed technologies and double-cropping while also accomplishing significant greenhouse gas reductions and promoting biodiversity, according to a new analysis by Dr. Bruce Dale and colleagues at Michigan State University.
Their analysis, published as an open access paper in the ACS journal Environmental Science & Technology, found that while using less that 30% of total US cropland, pasture and range, up to 400 billion liters (106 billion gallons US) of ethanol can be produced annually without decreasing domestic food production or agricultural exports. Their approach reduces US greenhouse gas emissions by up to 670 Tg CO2-equivalent per year—more than 10% of total US annual emissions—while increasing soil fertility and promoting biodiversity. It also eliminates the indirect land use change (ILUC) effect.
Our analysis shows that the US can produce very large amounts of biofuels, maintain domestic food supplies, continue our contribution to international food supplies, increase soil fertility, and significantly reduce GHGs. If so, then integrating biofuel production with animal feed production may also be a pathway available to many other countries. Resolving the apparent “food versus fuel” conflict seems to be more a matter of making the right choices rather than hard resource and technical constraints. If we so choose, we can quite readily adapt our agricultural system to produce food, animal feed, and sustainable biofuels.—Dale et al.
More than 80% of total agricultural production in the United States is used to feed animals, not human beings directly; most animal feed is produced for cattle, which are “nutritionally versatile animals”, Dale et al. note. In their study, they analyzed only the 114 million ha of cropland used now to produce animal feed, corn ethanol, and exports. Cropland used for direct human consumption, forests, grassland pasture, and rangeland are not considered. Thus, they note, the analysis provides an example of what is technically feasible, not an upper limit on US biofuel production.
For the study, they considered two land-efficient animal feed technologies: ammonia fiber expansion (AFEX) pretreatment to produce highly digestible (by ruminants) cellulosic biomass and leaf protein concentrate (LPC) production.
During AFEX, concentrated ammonia is contacted with cellulosic biomass at moderate temperatures, resulting in greatly increased production of fermentable sugars by enzymatic hydrolysis. AFEX increases the digestibility of cellulosic biomass for ruminant animals while increasing protein production in the animal rumen due to the addition of ammonia-based byproducts.
Although extensive feed testing and commercial applications have not yet been introduced, AFEX-treated rice straw has been successfully included in dairy cattle diets, and tests with switchgrass and corn stover have shown increased cell wall digestibility when exposed to rumen microorganisms.
High-protein LPC products are generally produced by first pulping and then mechanically pressing fresh green plant matter. The resulting protein-rich juice is then coagulated and dried. The remaining fibrous material is depleted in protein, but is still suitable for animal feed or biofuel production.
Animal feeding operations can be adapted to these new feeds, thereby freeing land for biofuel production, according to the authors. They also considered aggressive double-cropping, thereby increasing the total biomass produced per ha.
The researchers built a nonlinear optimization model to determine either the maximum ethanol production or maximum GHG reduction available from the 114 million ha of land. Either ethanol production or GHG reduction was maximized by varying the amount of land dedicated to each type of crop as well as how each crop is used subject to constraints regarding animal feeding, export requirements, and biodiversity. The model is limited in that it does not consider spatial parameters (such as variance in yields), temporal parameters (such as increasing population or crop yields), nor does it consider other policy or behavioral shifts such as changing human diets away from red meat consumption.
We believe our analysis is conservative in that it under predicts potential GHG reductions and biofuel production. For example, our analysis does not deal with (i) changing dietary trends which might reduce the need for animal feeds, (ii) more efficient use of grassland pasture and range, (iii) utilization of cellulosic residues other than corn stover, (iv) higher CBC yields, (v) more use of double crops beyond the one-third limit imposed in our analysis, or (vi) any biomass derived from forests. Each of these factors would likely increase biofuel production and further reduce GHG emissions while also reducing pressure on agricultural land. Except for possible increases in nitrate emissions, environmental services such as enhanced biodiversity, increased soil organic matter, and reduced GHG emissions are well served by the approaches outlined here.
...As noted, the technologies that provide most of the benefit to food and biofuel production are extensive double cropping and large scale production of diverse cellulosic crops appropriate to different regions of the country. These are not exotic, expensive, or high risk technologies. Considering their large benefits to energy security and climate security, extensive double cropping and production of diverse cellulosic crops deserve more study for widespread application in integrated biofuel and animal feeding systems than they have received to date.—Dale et al.
Bruce E. Dale, Bryan D. Bals, Seungdo Kim, and Pragnya Eranki (2010) Biofuels Done Right: Land Efficient Animal Feeds Enable Large Environmental and Energy Benefits. Environ. Sci. Technol., Article ASAP doi: 10.1021/es101864b