Will this happen again next year? What if farmers decide against crop rotations and plant corn on the same fields, year after year? Or, what if farmers begin growing biomass crops such as switchgrass for the production of ethanol from plant fibre? Will soil lose fertility? Will erosion increase? Will the amount of energy needed to produce biofuels go up or down? Will the bioeconomy be sustainable?
These are just some of the many questions that Robert Anex and colleagues from Iowa State University (Ames, Iowa) and Dartmouth College (Hanover, New Hampshire) are attempting to answer in their research (Crop Science 47 1327).
They are looking into the transition towards an agriculture that produces biomass as well as food and fibre. The researchers believe that "the development of biomass-based crops production systems can have as profound an impact on agriculture and its environmental footprint as it does on energy security and the global climate".
Whether this has a positive or a negative impact "will depend largely on how biomass feedstocks are produced and converted, and the extent to which these two activities are integrated".
The paper reports that as much as 78% of the nitrogen fertilizer needed for crops could be recovered from an integrated biological and thermochemical process that converts switchgrass to ethanol. The study says such nutrient recovery and recycling could significantly improve the sustainability of biomass production and the amount of energy required to produce ethanol from plant fibre.
The researchers say the nutrient recovery could happen this way: plant fibre would be converted to liquid fuels by pre-treatments and fermentation. The co-products of fermentation would be dried and heated to turn the solids into gases. The gasification would leave plant nutrients in the resulting ash and ammonia. The nutrients in both streams could be recovered and returned to the fields that produced the biomass.
And that potential for nutrient recycling means there's potential for a new kind of agriculture feeding a sustainable bioeconomy.
"By creating a large, new domestic demand for agricultural products, the advent of commercial-scale conversion of biomass into ethanol and other industrial chemicals is likely to have a strong influence on the design of agricultural systems," the researchers wrote. "The possibility of recycling nutrients from the biorefinery to the agricultural system that produces the feedstock may allow substantial improvements in both sustainability and production efficiency."
Simulation and planning
Sustaining biomass production is a complex system, however, and one that depends on many variables such as soil type and slope, soil organic matter and the amount of biomass actually harvested.
To help farmers begin to understand how collecting biomass from their fields may affect soil fertility, erosion, energy needs, labour and the bottom line, Anex and a team of Iowa State researchers have added bioeconomy elements to I-FARM, a free Web tool that helps farmers simulate and plan various changes to their operations. Its focus is on the upper-Midwest, but weather and soils data from 28 states are accessible from its database.
In one simulation, the I-FARM research team studied the effects of harvesting corn stalks and leaves on three farms in north-west Iowa's Palo Alto County. One grain farm harvested no stover, one harvested 1,809 dry tonnes of stover a year and the other harvested 3,077 dry tonnes a year.
The simulations found the farm that harvested the most stover also needed the most fertilizer, had the most erosion and barely returned sustainable levels of organic matter to the soil. That farm also recorded the highest net farm-income before taxes.
Anex's study of the sustainability of the bioeconomy is being supported, in part, by grants from the US Department of Agriculture, the US Department of Energy and the National Science Foundation.
The studies are helping researchers answer some questions about the sustainability of agriculture in a bioeconomy, Anex said. But there are still many questions about how everything would fit together in a new agricultural system.
"Despite the promise of alternative crops and cropping systems – as well as the nutrient recovery and recycling concepts examined here – there are still many questions that remain about their practical implementation," write Anex and the other researchers in their paper. "The issues that have been addressed here and the questions that have been raised, are only a small subset of those that must be addressed if we are to usher in a new and beneficial agricultural revolution."