Nutrient supply and neutralizing value of alfalfa stem gasification ash

Energy generation from biomass is an environmentally sound alternative to other energy producing technologies. Pilot studies have indicated that alfalfa (Medicago sativa L.) is a suitable feedstock for energy generation via the gasification process. The resulting ash is a potential liming agent and a source of plant nutrients. A growth chamber study was conducted with three soils to evaluate the potential use of this ash as a soil amendment. Corn (Zea mays L.) received 13 treatments: control, K and/or P fertilizer, seven ash rates (0.6 to 14.6 g ash kg^-1 soil), and one ash rate with K or P fertilizer. Soil pH increased with ash application on all soils. Ash application increased ammonium acetate-exchangeable K, Ca, and Mg, and Olsen P in soil and decreased DTPA-extractable soil Fe, Mn, Ni, and Pb. Averaged across the three soils, slopes of the cations recovered in plant and soil vs. cations applied in the ash were 0.48, 0.21, and 0.22 of total ash K, Ca, and Mg, respectively (r² > 0.97). Ash significantly increased plant K and Mo, and decreased Mg, Mn, and Zn concentration. Tissue P concentrations were not affected by ash, but increased with P fertilizer. Phosphorus fertilizer increased plant dry mass (DM), but K fertilizer did not, thus K did not limit yield. Alfalfa stem gasification ash is a potential liming agent, a source of K, and would not lead to excessive accumulation of trace elements in soil or plants when applied at rates based on lime or K need.