The cultivation of biofuels – fuels derived from animal or plant matter – on marginal lands could meet up to half of the world’s current fuel consumption needs without affecting food crops or pastureland, environmental engineering researchers from America’s University of Illinois have concluded following a three-year study. The findings, according to lead author Ximing Cai, have significant implications not only for the production of biofuels, but also the environmental quality of degraded lands.
The study, the final report of which was published in the Journal of Environmental Science and Technology late last year, comes at a time of increasing global interest in biomass. The International Energy Agency predicts that biomass energy’s share of global energy supply will treble by 2050, to 30%. In March, the UK-based International Institute for Environment and Development called on national governments to take a “more sophisticated” approach to the energy source, putting it at the heart of energy strategies and ramping up investment in new technologies and research programmes.
The University of Illinois project used cutting-edge land-use data collection methods to try to determine the potential for second-generation biofuels and perennial grasses, which do not compete with food crops and can be grown with less fertiliser and pesticide than conventional biofuels. They are considered to be an alternative to corn ethanol – a “first generation” biofuel – which has been criticised for the high amount of energy required to grow and harvest it, its intensive irrigation needs and the fact that corn used for biofuel now accounts for about 40% of the United States entire corn crop.
A critical concept of the study was that it only considered marginal land, defined as abandoned or degraded or of low quality for agricultural uses, Cai, who is civil and environmental engineering professor at the University of Illinois in the mid-western United States, told chinadialogue.
The team considered cultivation of three crops: switchgrass, miscanthus and a class of perennial grasses referred to as low-impact high-diversity (LIHD).
Researchers considered multiple scenarios for land availability. The first was only idle and vegetated land with marginal productivity; the second included use of degraded or low-quality cropland for growing switchgrass and miscanthus; a third scenario brought in LIHD grasses grown on marginal grasslands; and a fourth eliminated current cropland and pastureland from the total. Forestland was not considered in any of the scenarios. In all scenarios, the researchers assumed that rainfall would be the only means of watering the biofuel crops. They assessed physical perspectives – including soil properties, soil quality, land gradient and regional climate.
Focusing their analysis on the fourth scenario, the research team found that an estimated land area of 11.1 million square kilometres could be available globally. Land in Africa alone represented one-third of the total, while South America and Africa together contributed more than half. Global biofuels production could meet 26% to 55% of current world liquid fuel consumption needs under this scenario. The large range in percentage reflects variables in productivity of the biofuel crops, weather and other factors such as labour and machinery, Cai said.
According to Cai’s figures, about 1.2 million square kilometres could be available in the United States for growing these crops, 1.5 million in China, 1.1 million in Europe and 1.5 million in India. He noted that, even if only the lowest impact scenario was achieved, the United States would still be able to produce a quantity of biofuel that would more than meet the federal mandate of 36 billion gallons (around 136 billion litres) for use in the nation’s transportation sector by 2022. Only about 50% of US marginal lands are in agricultural production.
In China, it is a different story because the majority of marginal lands are currently under cultivation, Cai said. “What we found in China is that, of the 152 million hectares, about 88% is currently used for agriculture. That means in China, if we want to use that land for biofuel production, farmers will have to switch from the conventional crops to biofuel crops. There’s a tradeoff. The profit might be higher with biofuel crops, but it would affect food production.”
The research team also calculated net energy gain for six countries or regions and found that net energy savings under the fourth scenario – where current cropland and pastureland was eliminated from total available land – would be 49 to 105 gigajoules per hectare, equivalent to around 294 to 630 barrels of oil per hectare.
The authors note several caveats to the study. One is that biofuel production could aggravate water stress in some regions because of the water needs of refineries. Generally, second generation biofuels require more processing than corn ethanol. Another is distribution of the available land. If biofuel development were to proceed along the lines suggested by this study, more than half would originate in Africa and South America, whereas the largest demand for fuel is in the United States, Europe and Indochina, Cai said. “That means biofuel shipment would be a major issue. If we follow that kind of development path, a lot of energy would have to be shipped from Africa and South America to other places. That means a huge investment in infrastructure development.”
Biofuel development and growth of perennial grasses in marginal lands would also have significant environmental benefits for the land itself, Cai said. Beyond their low water, fertiliser and pesticide requirements, the roots of perennial grasses prevent soil erosion and siltation of river systems.
Switchgrass has been steadily gaining advocates in the United States in recent years. Test plots grown at Auburn University, in the south-eastern state of Alabama, have yielded up to 15 tonnes of dry biomass an acre (around 4,000 square metres), with average five-year yields of 11.5 tonnes, enough to make around 4,400 litres of ethanol per acre per year. A grass that can grow to more than three metres tall, switchgrass has roots that extend almost that far into the soil, making it a great crop to control soil erosion. It has also been found to restore vital nutrients to farmed-out soil. It can be harvested once or twice a year, with replanting needed about every 10 years.
Miscanthus, a giant perennial grass also known as Chinese silvergrass, has been found to be even more efficient in growth and fuel output than switchgrass. The University of Illinois is the lead American institution in miscanthus research. A research team at the US Department of Energy’s Oak Ridge National Laboratory is exploring the potential of switchgrass, as well as other biofuels.
While LIHD crops have a lower ethanol yield than switchgrass and miscanthus, they have minimal environmental impact and are similar to grassland’s natural vegetative cover. Researchers estimated that LIHD biomass has a net energy gain of about 17.8 gigajoules of energy (the equivalent of about 2.9 barrels of oil) per 10,000 square metres. They define net energy as “the difference between the amount of energy gained from the biomass harvest and the energy consumed for feedstock production and ethanol production.”
Switchgrass and miscanthus average a net energy gain of 60 to 140 gigajoules (9.8 to 23 barrels of oil) per 10,000 square metres, depending on soil, climate and agricultural inputs. There is controversy over the net energy gain for corn ethanol because of the amount of fuel needed for cultivating it, including energy outputs for fertilisers and pesticides, with some researchers saying its net energy production is marginal and comes at a net carbon debt. Cai estimates the net energy gain of corn to be 16 to 23 barrels of oil per 10,000 square metres. Total US ethanol production is expected to be about 13.5 billion gallons (51.1 billion litres) in 2011, the equivalent of about 321 million barrels of oil.
Cai is working on another study — the effects of climate change on the map of available marginal lands — and said his findings show that land availability in China is likely to increase because of increased precipitation in some regions. By the same token, other parts of the world will see a loss of lands suitable for biofuel production.
Cai said he hopes the study on potential biofuel production will “provide a physical basis for future research. We hope local researchers use our data to refine this study in their region,” he said. “The purpose of this study is to show a global picture. We are open to sharing our data. Any country can use our data and methodologies.”
Joan Melcher is a freelance journalist based in the United States.
Homepage image from Shenghung Lin
