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Sequential chemical extraction and synchrotron-based XANES spectroscopy techniques were used to identify P species in two ashes before and after addition to a prairie soil. The used ashes were: meat and bone meal ash (MBMA) and dried distillers grains ash (DDGA) plus mineral P fertilizer (MP) for comparison. Soil treated with MP contained higher content of resin-Pi and NaHCO 3 -Pi followed by DDGA and MBMA. The MBMA amended soil had the highest (47%) proportion of the soil P contained in recalcitrant HCl extractable fraction, reflecting more Ca-bound P present and being formed in soil after application. Analysis of both ashes with XANES spectroscopy before application to soil revealed that MBMA had strong spectral features consistent with hydroxyapatite (Ca 5 (PO 4 ) 3 (OH)). DDGA exhibited spectral features consistent with a mixture of several Mg and K phosphate salts rather than a single mineral species. The distinctive features in the XANES spectra of both ashes largely disappeared after amendment to the soil, suggesting transformation to different P forms in the soil after application. It is also possible that the added amount of P to the studied soil via DDGS or MBMA was small enough so that P speciation is not different from the background P level.Phosphorus is an essential element for plants, and its supply in soil is critical in maximizing crop production and improving food and feed quality. The global demand for phosphorus fertilizer is projected to increase by 50-100% by 2050 to enable sustained food production for a growing world population 1 . Complete reliance on phosphorus fertilizer manufactured from mined phosphate rock may not be a good strategy for sustained crop yields, stimulating the need to find alternative phosphorus sources and recycle more effectively the P that is contained in agricultural by-products. One option is the utilization of ash generated from organic materials via the gasification process, a thermal breakdown of organic materials under high temperature (800-900 °C) in presence of oxygen 2 . Application of this combustion technology to meat and bone meal (MBM) and dried distillers grains (DDG) as a means of providing additional nutrient and energy recovery has gained interest 3-5 . The gasification of MBM and DDG produces ash byproduct that was noted to have high content of total P, and with potential as P fertilizer source 6 . However, the P forms in the ash and ash amended soil were not examined in this study. In general, ashes derived from various feedstocks, such as poultry litter, turkey manure and crop residues have a positive impact on crop yield and soil properties when added to soil [7][8][9] . However, the effects on P availability and mobility will depend on the P forms produced in the amended soil, and may vary depending on feedstock and gasification conditions. Furthermore, P in ash may exist in different forms and availability levels, and when added to soil, it is anticipated to interact/associate with soil constituents and reside in different forms as well. Ther...

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