Balancing Bioenergy Opportunities on Your Natural Resources Base

With rising land prices and global interest in bioenergy opportunities, many producers are being tempted to garner extra cash by selling both their grain and crop residues. As consultants to these decision makers, what advice should you give? This presentation will focus on the multiple roles that crop residues provide by protecting soils from wind and water erosion, recycling essential plant nutrients, sequestering carbon, and serving as an important food source for the numerous organisms living in the soil. Data collected for the past three years from continuous corn and corn-soybean sites near Ames, IA will be discussed along with information from several other ARS locations that are participants in a cross-location project known as REAP (Renewable Energy Assessment Project). At the Ames sites, a one-pass harvesting system was used in 2005 to collect grain and (1) the top 50% of the plant, (2) bottom 50% of the plant, (3) all harvestable stover, or (4) no stover. At the rotated site, soybean was grown in 2006 without applying any additional fertilizer. When the soybean crop was harvested, there was a 50% decrease in grain yield where corn stover had been removed compared to where it was returned to the soil. Further investigations suggest this yield decline was probably caused by a relatively low soil test P and K status when the residues were first removed. Continuous corn yielded more where the previous crop’s residue was harvested than where it was returned, but the  3rd year corn yields averaged 10 bu/acre less than 2nd year corn even though fertilizer N rates were twice as high. This reconfirms a well-documented yield penalty associated with continuous corn on many Midwestern soils, and emphasizes that the merits of crop rotation must not be forgotten as management plans are made. The need for higher N fertilization rates to support continuous corn for bioenergy will almost certainly lead to greater N-leaching loss and further contamination of surface and ground water resources. Using published data for the Midwest, the REAP team has documented that to sustain soil carbon, corn yields must be at least 150 bu/ac and the amount of tillage must be minimized. The presentation will conclude with a vision for how agriculture as a whole can meet multiple demands for food, feed, fiber, and energy in an economically viable and sustainable manner that truly balances short-term economic opportunities with long-term natural resource stewardship.

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Douglas Karlen Research Soil Scientist
USDA ARS National Soil Tilth Laboratory (NSTL)
Doug.Karlen@ars.usda.gov


Dr. Doug Karlen has nearly 30 years of experience working as a Research Soil Scientist for the USDA Agricultural Research Service, first for 10 year at the Coastal Plains Soil and Water Conservation Research Center in Florence, SC, and now for the past 20 years at the National Soil Tilth Lab in Ames, Iowa. He has authored over 250 papers and is a co-editor for "Sustainable Agriculture Systems" and "Agricultural Utilization of Urban and Industrial By-Products.” He has held leadership roles in soil and crop professional organizations and has received numerous honors and awards. Doug uses a systems approach involving producers, action agencies, non-government organizations (NGOs), agribusiness, and other state and federal research partners, in order to quantify the physical, chemical, and biological effects of conventional and organic farming practices. The effects of tillage, crop rotation, nutrient management, and other decision-based factors are evaluated by determining how they affect soil quality, crop productivity, plant nutrient availability, and nutrient or soil losses from various soil types and landscape positions.