November 2004 Newsletter

Guest Editorial: Unintended Consequences of Utilizing Agricultural "Wastes" for Energy

By David Lauer

I enjoy your newsletter and I am supportive of alternative energy technologies that I hope in the long term will make the Northwest and U.S. more self-sufficient with sustainable alternatives. However, regarding biomass energy production specifically from agricultural residues, there are some potential unintended consequences that need to be assessed and factored into the equation of the sustainability of this particular avenue of developing alternative energy production. My concerns are derived from my knowledge in the areas of agronomy specifically soils, plant nutrition, and nutrient cycling and also air quality issues.

I have a basic objection to the classification of all agricultural residues as waste materials and the corollary concept that converting this "waste" to energy is perhaps the most desirable use of this resource. One principle of agricultural production that has recently been rediscovered is that of maintaining sustainability of these systems. The concept of "factory farming" driven by low-margin-high-volume economics is causing perturbations that I personally do not believe will be sustainable in the long run. Farming systems in the not too distant past were diversified with integrated animal and crop production in close proximity that allowed recycling of agricultural residues and accompanying nutrients essentially within the farming unit. A combination of proper use of soil conservation practices to avoid soil loss coupled with well-managed use of the organic matter and nutrients in agricultural residues results in healthy soil both physically and chemically. Good soil health maintains a reservoir of mineral nutrients, maintains water-holding capacity, and stabilizes soil against water and wind erosion. Good soil health is very dependent on maintaining a good organic matter content and healthy microbial ecosystem within the soil.

Chemical fertilizer and its management is a very important aspect of nutrient management in agricultural production systems. However, chemical fertilizers cannot completely substitute for the benefits of having organic matter inputs into the soil. A balanced approach is needed that utilizes both chemical fertilizers and organic matter coming from agricultural residues. Soil erosion control is ultimately reliant on proper use of agricultural residues. Recycling residue from agricultural crop production back into the soil is an essential component of long-term sustainability of the soil-plant system in agricultural production.

One adverse effect that results from factory farming or concentrated animal feeding operations (CAFOs) is that frequently the feed production and animal production operations are geographically separated. Feed is transported long distances by truck and rail from crop production areas to the livestock production facility. As a result, the organic carbon matrix of and the nutrients contained in the feed are concentrated at the location of the CAFO. The majority of carbon and nutrients are passed through the animals as manure with only a small fraction flowing out in the product (meat, milk, or eggs). In many cases the land available on which the manure can be placed for in situ recycling via microbial action is insufficient or not appropriate for feed production. This type of animal and feed crop production system simply does not have the capacity to absorb the nutrient loading or biological oxygen demand (BOD) for proper recycling.

Overloading the soil and CAFO location with nutrients and BOD causes severe odors and potential contamination of surface and ground water with excessive nutrients and BOD. The highly concentrated nature of these facilities also causes air emissions important in air quality including volatile organic compounds (VOCs), ammonia, and primary small particulate matter. Ammonia in addition is precursor to secondary small particulate matter formation in the ambient air upon reaction with airborne nitrate, sulfate, and chloride. Reduced sulfur compounds are responsible for much of the odor and the associated H2S is directly toxic.

Overall, CAFOs associated with severe geographic dislocation of mass flows (feed, manure, agricultural residues) in agricultural production systems introduce severe perturbations in sustainable nitrogen and carbon cycling as well as for other mineral nutrients such as phosphorus. Another undesirable effect is that in the areas where feed is produced, the soil is being mined for nutrients and organic matter as these are hauled away to distant animal feeding operations. Replacement nutrients are supplied as commercial fertilizers at considerable cost of energy for production of the fertilizer. The cost of back-hauling manure is usually prohibitive with a very short threshold distance.

Sufficient return of organic matter (carbon) to soils in the feed producing areas may or may not be occurring. Some agricultural producers are hoping to get credit for carbon sequestration or net accumulation of carbon to participate in mitigation of release of greenhouse gases. This requires an increase in the long-term stable organic matter content of the soil. The unsustainable nutrient and residue recycling scenario above is directly opposed to net soil organic matter (carbon) increase in feed crop production areas. Energy production using agricultural residues at CAFOs that are geographically remote from feed production areas abets these undesirable effects. Energy derived from methane from anaerobic digestion, pyrolysis, or any process that ultimately results in combustion in effect moves carbon sequestered in stable soil organic matter into the atmosphere as CO2.

Because of the high energy requirement for dewatering of many residues and increased ammonia losses from the drying process anaerobic digestion is usually the preferred avenue of energy production from animal wastes. However, anaerobic digestion to produce methane for energy production leaves a residue of its own, which is nutrient rich in a semi-stabilized organic matter matrix. Unless deliberately controlled, ammonia losses from anaerobic digestion are greater in quantity compared to leaving a greater fraction of the nitrogen in its original organic form in the manure or other agricultural residue.

Direct harvest of agricultural residues for energy production, mischaracterized as waste material, that is normally intended for reincorporation (recycling) back into the soil is an even more blatant disruption of normal cycling of nitrogen, carbon, and certain other minerals. In contrast, biomass production strictly for the purpose of energy production when properly managed would likely be no more harmful than ordinary crop production.

In summary, there are a number of potential unintended effects from introducing the energy production from agricultural residues into already complex and severely perturbated biological systems of animal and crop production. What is needed is a systems approach with mass flow modeling that evaluates the complete soil to feed to residues to energy production processes. Comparing the potential consequences of alternative scenarios to assess the fate of nitrogen, carbon, and other nutrients could lead to better management and policy decisions.

David Lauer is Director of the Benton Clean Air Authority in eastern Washington.