Environmental Protection

Iowa State Study: Less Fossil Energy May Require More Labor

Conventional agriculture production relies heavily on fossil fuels, particularly in its ability to provide energy at a low cost. However, the uncertain future of fossil fuel availability and prices point the need to explore energy efficiencies in other cropping systems.

Matt Liebman, Michael Cruse, and their colleagues at Iowa State University conducted a six-year study to compare energy use of a conventionally managed corn and soybean system with two low-input cropping systems that use more diverse crops and manure applications but also use less fertilizer and herbicides. The results (pdf, abstract) were published in the May/June 2010 edition of Agronomy Journal, published by the American Society of Agronomy.

The two input systems consisted of a three-year rotation of corn-soybean/small grain/red clover and a four-year rotation of corn-soybean-small grain/alfalfa-alfalfa. Between 2003 and 2008, nitrogen fertilizer inputs in the 3-year rotation decreased 66 percent and decreased 78 percent in the 4-year rotation. Herbicide use decreased 80 percent in the three-year rotation and 85 percent in the four-year rotation. Despite the energy input reduction, corn and soybean yields matched or exceeded the conventional system yields.

Did the application of manure decrease the fossil fuel energy costs? Manure prices are dependent on local economic conditions, but the two low-input systems used 23 percent to 56 percent less fossil energy than conventional systems. To analyze the energy and economic costs of manure application, the researchers used two approaches. One where manure was a waste product of livestock and essentially free of cost except for the energy used in its application, and a second approach as if the costs of manure were the same as commercial fertilizers. As a low economic input, manure can return $249 per acre, or $28 to $38 under high economic input for four and three-year systems, respectively.

Most of the fossil energy input for all systems was from grain drying and handling. Conditions in northern latitudes, where farmers have limited time to allow grain to dry in the field, make it difficult to reduce this cost. The researchers point out, however, that growing corn less frequently in a rotation sequence can reduce the need for grain drying with fossil energy.

The three- and four-year rotation plans rely on agriculture systems where livestock feeding, manure application are integrated into crop production practices. “Iowa has a long history of mixed crop and livestock farming, although these operations do require more management and labor,” said Liebman. “If fossil energy costs rise steeply, we may see more of them again.”

“It’s hard to predict the exact details of what the future will bring us,” said Liebman. “But results of this study show that we do have options for maintaining high farm productivity and profitability while substantially reducing our dependence on fossil energy.”

The research team was funded by the Leopold Center for Sustainable Agriculture and the U.S. Department of Agriculture. It is expanding its activities into measurements of effects of the different cropping systems on water quality, greenhouse gas emissions, and soil carbon and nitrogen dynamics.

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