Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2001
Publication Date: N/A
Citation: Interpretive Summary: Biomass crops are candidates for sustainable, alternative fuel sources for the growing worldwide electrical energy demand. Biomass materials are gasified (similar to burning) to heat water that, in turn, drives turbines to make electricity. Most biomass research has emphasized grasses and trees, but the net amount of energy produced by these biomass crops is limited because these plants need nitrogen fertilizer to produce high yields. Nitrogen fertilizer requires energy to manufacture. Annual grass crops also require fossil fuel inputs for yearly establishment, and the soil is often subject to erosion between plantings because plant residues are removed. Alfalfa is a high-yielding forage crop that can obtain nearly all the nitrogen it needs from the atmosphere through symbiotic fixation. It also 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 make electricity. Ash is the main byproduct from biomass fuels, an 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. This research confirmed the results we got in an earlier experiment, that alfalfa stem ash is a good source of potassium to corn, may provide phosphorus under certain soil conditions, and is an effective liming agent to 'sweeten' acid soils. No problems were observed due to metals or other compounds in the ash. Even though alfalfa stems are not yet being used for biomass energy, our research showed that alfalfa stem ash would be a useful product for farmers, rather than a waste that must be disposed of by the electrical supplier.
Technical Abstract: Energy generation from biomass is an environmentally sound alternative to other energy producing technologies. Development of beneficial uses for ash generated from bioenergy production will increase its economic competitiveness. Pilot studies have indicated that alfalfa (Medicago sativa L.) is a suitable feedstock for energy generation via the gasification process. This ash contains K, P, and other elements, and might be a potential liming agent. A growth chamber study was conducted with three soils to evaluate the potential use of ash from gasification of alfalfa stems as a fertilizer and/or liming agent for corn (Zea mays L.). Treatments included control, K and/or P fertilizers, and seven ash rates (0.6 to 14.6 g/kg). One g/kg of ash increased the pH of the three soils by 0.07 to 0.19 units. Ash application was positively correlated with exchangeable K, Ca, Mg, and extractable P in soil samples collected after harvest. DTPA extractable Fe, Mn, Ni, and Pb significantly decreased, mainly due to liming effect of ash. Ash significantly increased plant K and Mo and decreased Mg and Zn. Tissue P concentrations were not affected by ash but increased with P fertilizer. Phosphorus fertilizer increased plant biomass but K fertilizer did not, thus K did not limit yield. High rates of ash decreased plant biomass in the sandy soil and increased biomass in the low P soil. Alfalfa stem gasification ash is a potential liming agent, a good source of K, and a modest source of P. Its application at agronomically reasonable rates did not lead to excessive accumulation of trace elements in soil or plants.