George Bush has called for the production of 35 billion gallons of ethanol by 2017, an amount equivalent to roughly 15% of US liquid transportation fuels. But increased use of fertilizers and pesticides for growing biofuels could impact the quality of groundwater, rivers and coastal and offshore waters, says the report. Corn generally receives more fertilizer and pesticides per acre than soybeans or mixed-species grassland biomass. So switching fron other crops or non-crop plants to corn is likely to lead to much higher application rates of highly soluble nitrogen.
That said, techniques such as injecting fertilizer below the soil surface, using controlled-release fertilizers with water-insoluble coatings, and optimizing the amount of fertilizer applied could all reduce nutrient pollution.
A National Research Council committee found that in many parts of the US agricultural shifts to growing corn as well as expanding biofuel crops into regions with little agriculture - especially in dry areas - could increase pressure on water resources. Water requirements for the same crop differ from region to region - for example in the Northern and Southern Plains, corn generally uses more water than soybeans and cotton but the reverse is true in the US's Pacific and mountain regions. Water demands for drinking, industry, hydropower, fish habitat and recreation could all compete with the use of water for biofuel crops.
What's more, there's not enough data available to predict the effects on water of future large-scale production of crops such as switchgrass and native grasses for use as biofuels. And it's possible that biofuel crops could be grown by different techniques to food crops, employing methods such as irrigation with wastewater that's not suitable for use with food crops.
In order to minimize soil erosion, the committee proposes the use of perennial crops for biofuels, such as switchgrass, poplars or willows, or the employment of prairie polyculture, which can hold soil and nutrients in place better than most row crops. Conservation tillage and leaving most of the cornstalks and cobs in the field after harvest could also be beneficial.
But it's not just growing the crops themselves that will boost water demand: biorefineries for converting the biomass into ethanol will also consume water. A biorefinery producing 100 million gallons of ethanol a year would use the same amount of water as a town of about 5,000 people, although new water recycling and other manufacturing technologies could reduce this amount in future.
The Council also presented its findings at a colloquium in July.