Photo: Tom Campbell, Purdue agricultural communication
Removing corn stover to produce cellulosic ethanol requires careful management to avoid adding greenhouse gas emissions and soil erosion to the environment, say Purdue University researchers in a new study entitled “Environmental and Economic Trade-Offs in a Watershed When Using Corn Stover for Bioenergy.”
“Some crop rotation and tillage combinations are more environmentally benign than others,” said Ben Gramig, Purdue agricultural economist and the study's lead researcher. “But there are water quality and greenhouse gas trade-offs when collecting stover.”
The researchers examined the environmental effects and costs of stover collection from eight corn-soybean rotation and continuous corn systems in a watershed typical of the eastern Corn Belt. They made comparisons by combining results from watershed and greenhouse gas computer simulation models and minimizing the cost of stover collection to select which farming practices to use in an agricultural watershed.
Gramig, Purdue agricultural and biological engineer Indrajeet Chaubey and graduate researchers Cibin Raj and Carson Reeling found that a continuous corn system with conventional tillage and a 52 percent removal of the stover from the field released the most greenhouse gas and soil sediment per acre: 3.5 tons and 1.1 ton, respectively. That same acre of land yielded 2.7 tons of stover.
If all the nitrogen contained in the stover that is removed must be replaced and there is more continuous corn cultivation, researchers found that greenhouse gas emissions from cropland may increase.
At the low end of the environmental impact scale, a no-till corn-soybean rotation where 38 percent of the stover was removed emitted 2.7 tons of carbon dioxide per acre and yielded 2 tons of stover.
Removing stover increased production costs over the predominant corn-soybean rotation in place today, the researchers found. Most of that cost is attributed to replacing nitrogen contained in stover. Stover removal was found to have the lowest cost when collected from corn grown in rotation with soybeans.
More study is needed to identify less environmentally harmful stover removal practices, Gramig said.
“In the meantime, farmers can use no-till to reduce the amount of sediment loss,” Gramig noted. “Additional practices, such as the use of cover crops, are going to be necessary if we want to try to reduce greenhouse gas loss. We also need to determine what the correct nitrogen replacement rate is to maintain long-term soil productivity while minimizing nitrogen loss, whether to the atmosphere or to waterways.”
The study is available at http://dx.doi.org/10.1021/es303459h .
A link to a video of Gramig discussing the Purdue corn stover removal study is available at http://www.youtube.com/watch?v=PFUgqr7oDJA&feature=youtu.be