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Potential for using biofuel, crop and animal processing by-products as soil amendments to increase fertility

Schoenau, J.. 2009. Agriculture Development Fund Project


Controlled environment experiments were set up in 2008 to evaluatethe effect of adding various biofuel and crop processing co-products to soil as organic amendments to increase soil fertility, crop growth, soil organic matter and microbial activity. Amendments evaluated included dehydrated alfalfa, wet and dry distillers grain, thin stillage and glycerol applied at different rates in comparison with urea fertilizer. Canola was grown as the test crop in amended pots, and plant yield, composition and soil properties were measured after five weeks. The same treatments were prepared and used in an incubation experiment in which carbon dioxide, nitrous oxide gas,and nutrient ion release by soil microbial populations was assessed. The alfalfa, distillers grain and stillage products were found to be effective soil amendments for increasing canola biomass yield. Per unit of nitrogen added, yields were less than that of urea when nitrogen was the only limitation, due to only a portion of the nitrogen in the amendment becoming available over the five week period. However, when nutrients other than nitrogen were limiting, canola dry matter yields with organic amendment approached or exceeded that of urea, due to the ability of the amendments to supply other nutrients in addition to nitrogen. Glycerol, an amendment thatonly contains carbon, hydrogen and oxygen, was effective in increasing soil organic carbon content, but required supplemental fertilizer to account for nutrient tie-up by microorganisms during decomposition in the soil. The amendments did not have any biologically significant effects on soil chemical parameters measured including soluble metals, pH or salinity. Some initial reduction in germination and emergence of canola plants at the highest rate of distillersgrain was observed, the nature of which was not identified. Application of solid amendments like alfalfa and distillers grain enhanced microbial activity to the greatest extent as revealed in carbon dioxide gas production. Per unit of nitrogen added, urea resulted in the greatest production of nitrous oxide gas and alfalfa the least. The supply rates of nitrate to PRS probes during the incubation were closely related to patterns in nitrous oxide production, indicating that nitrification is likely the main source of nitrous oxide production when organic and inorganic fertilizer amendments are initially added to the soil.