Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2000
Publication Date: N/A
Citation: Interpretive Summary: Biomass crops are candidates for sustainable, alternative fuel sources to meet the growing worldwide electrical energy demand. Biomass materials are gasified (or burned) to heat water that, in turn, drives turbines to make electricity. Most biomass research has emphasized grasses and trees, as these crops often produce the greatest yield of burnable material. A large drawback of these plants is their need for nitrogen fertilizer to produce high yield, which requires a lot of energy to manufacture. In addition, annual grass crops require large energy inputs for yearly establishment, and the soil is often subject to erosion between plantings. Alfalfa is a high-yielding forage crop that obtains nearly all the nitrogen it needs from the atmosphere through symbiotic fixation. Furthermore, it protects and improves the soil as it grows and increases yields of succeeding crops. Alfalfa's stems are poorly utilized by livestock and could serve as fuel to omake electricity. As with coal, ash is the main byproduct from biomass fuels. Ash contains materials like plant nutrients and metals that are not burned away. As part of a large team effort to evaluate alfalfa as a potential biomass crop, we studied whether the ash produced from gasified alfalfa stems could be used as a fertilizer. We discovered that alfalfa stem ash was a good source of potassium, and that it was an effective liming agent to 'sweeten' acid soils. No problems were observed due to metals or other compounds in the ash. Alfalfa stems are not being used as a sustainable source of biomass energy yet, but our research has demonstrated that alfalfa stem ash would be a useful product for farmers, not a waste that must be disposed of by the electrical supplier.
Technical Abstract: Electricity generation from biomass is becoming an environmentally sound option compared to nonrenewable fuels. Pilot studies have demonstrated that alfalfa (Medicago sativa L.) stems are a suitable feedstock for energy generation via gasification. Developing beneficial uses for ash produced as a byproduct will enhance the economic viability of bioenergy. A greenhouse study was conducted to evaluate the potential use of alfalfa ash as a fertilizer and/or liming agent using corn (Zea mays L.). Two soils, a Hubbard loamy sand (low pH, low K, and high P) and a Barnes clay loam (high pH, high K, and low P) were used. Treatments included a control, K and/or P fertilizers, and six ash rates ranging from 0.2 to 6.4 g/kg (450 to 15,000 kg/ha). Ash application significantly increased K and decreased Mg concentrations in corn. However, neither plant P nor trace elements were affected by ash application. Elemental uptake by plants paralleled their respective concentrations. Soil pH increased linearly in the Hubbard soil with ash but was not affected in the Barnes soil. Ash application significantly increased salinity, Cl, extractable P, exchangeable K, Ca, Mg, and Na in both soils. Ash from gasified alfalfa stems appears to be a potential source of K and a potential liming agent for acid soils. When used at agronomically reasonable rates, alfalfa ash did not pose any risk of excessive accumulation of metals tested in soil or plants.