Biofuel Development Impacts on Water Quality

Land use and management have direct impacts on water quality. Thus, it is easy to imagine the different impacts on water quality from row crop production compared to perennial grass production. This contrast illustrates the range of impacts various bioenergy crop production systems will have on water quality. Simply, the impact of bioenergy crop production on water quality will depend on the type of crops grown and the management practices used to grow them. Much is known about the water quality impacts of some bioenergy crops, such as corn, but little is known about the impact of other potential crops. Currently, and for the foreseeable future, corn grain ethanol will be the dominant biofuel produced in the North Central Region. If cellulosic ethanol production becomes viable, the impact on water quality may be beneficial, but may vary.

Water Quality Impacts of Expanded Corn Grain Ethanol Production

There are several potential scenarios that could unfold to meet the increased demand for corn grain ethanol. Each of these scenarios will expand corn production in a different way, or onto different types of land, and so will have different potential impacts on surface and ground water quality. What is certain is that expanding corn production to more acres will increase the amount of tillage, fertilizer and pesticide use in the region.

It is likely that corn production will increase on all these fronts: expansion onto marginal land, cropping on former CRP land, changes in rotations, and Ecological Intensification. In each case, using appropriate best management practices to protect water quality will be essential.

Marginal Acres – Production could be expanded onto marginal land that is currently out of production because it is not economically productive. Cropping marginal lands can negatively impact both surface and ground water quality, because each additional acre of land brought into production adds a modest amount of contaminants into water. The potential negative impact of cropping marginal land, which requires even greater fertilizer inputs, will be proportionately greater yet.

CRP Acres Similarly, Conservation Reserve Program (CRP) land, currently sown to perennial grass, could be brought back into production. Much of this land is classified as highly erodible, which is the reason it was put into CRP. Cropping CRP land could result in significant increases in soil erosion and associated transport of nutrients and pesticides to surface water. Reversing 25 years of water quality benefits by removing land from CRP will have severe impacts on river, lake and reservoir water quality.

There are other factors besides ethanol demand pushing the expansion of corn production onto CRP lands. Studies in Iowa have shown a significant increase in a farmer’s willingness to plant CRP land when corn reaches $5.00 per bushel [2]. Also, Farm Bill policy has reduced the total number of acres allowed in CRP enrollment. These two factors, price and policy, added to ethanol demand, could create conditions where much CRP land is converted to corn production.

See the section “Landscape Conversion to Bioenergy Crops” for management recommendations to convert CRP to crop production.

Change in Crop Rotations If demand is very high, or if market forces dictate, continuous corn production could replace the rotations used today, resulting in recurring annual inputs for corn production and subsequent negative impacts on water quality. Surveys in Nebraska suggested price would be a strong motivator for converting from a corn-soybean rotation to continuous corn. However, farmers with wheat in rotation would be unlikely to switch to continuous corn [3].

Ecological IntensificationAnother alternative to meeting corn production demand is to increase the yield on current corn acres, without bringing new, marginal or highly erodible acres into production. Improved nutrient, water, and pest management through Ecological Intensification to increase yield, if done well, can provide increased yield without anticipated negative impacts on water quality (See the last section in this unit for more on Ecological Intensification).

Water Quality Impacts of Cellulosic Ethanol Production

If commercial cellulosic ethanol production using perennial crops becomes viable, then maintaining more acres in perennial grasses may result in much less impact on water quality compared to row crop production. Perennial systems have much lower losses of soil, nutrients and pesticides than do row crops, can be integrated into landscapes to improve water quality (e.g. grass buffers, strip cropping), and can be managed on marginal and highly erodible lands.

However, if cellulosic ethanol production using crop residues and stover becomes viable, there may be potential negative impacts to surface water quality. Removing too much crop residue can significantly increase soil erosion, with resulting losses of nutrients and pesticides. Also, some amount of returned crop residue is needed to maintain soil organic matter content.

Although cellulosic ethanol production may have some advantages for maintaining water quality, currently no such large-scale cellulosic bioenergy systems are in production.