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Greenhouse gas emissions and nutrient supply rates in soil amended with biofuel production by-products

Alotaibi, K.D. and J.J. Schoenau. 2013. Biology and Fertility of Soils. 49:129-141

Abstract

Ethanol production results in distiller grain, and biodiesel produces glycerol as by-product. However, there is limited information on effects of their addition on evolution of N2O and CO2 from soils, yet it is important to enable our understanding of impacts of biofuel production on greenhouse gas budgets. The objective of this study was to evaluate the direct effects of adding wet distillers grain (WDG), thin stillage (TS), and glycerol at three rates on greenhouse gas emissions (N2O and CO2) and nutrient supply rates in a cultivated soil from the Canadian prairies. The WDG and TS application rates were: 100, 200, or 400 kg N ha-1, whereas glycerol was applied at: 40, 400, or 4,000 kg C ha-1 applied alone (G-N) or in a combination with 300 kg N ha-1 (G N). In addition, conventional amendments of urea (UR) and dehydrated alfalfa (DA) were added at the same rates of total N as the by-products for comparative purposes. The production of N2O and CO2 was measured over an incubation period of 10 days in incubation chambers and Plant Root Simulator™ resin membrane probes were used to measure nutrient (NH4 -N, NO3--N, and PO4-3-P) supply rates in the soil during incubation. Per unit of N added, urea tended to result in the greatest N2O production, followed by wet distillers grain and thin stillage, with glycerol and dehydrated alfalfa resulting in the lowest N2O production. Cumulative N2O production increased with increasing the rate of N-containing amendments and was the highest at the high rate of UR treatment. Addition of urea with glycerol contributed to a higher rate of N2O emission, especially at the low rate of glycerol. The DA and WDG resulted in the greatest evolution of CO2 from the soil, with the thin stillage resulting in less CO2 evolved per unit of N added. Addition of N fertilizer along with glycerol enhanced microbial activity and decomposition. The amendments had significant impacts on release of available nutrient, with the UR treatments providing the highest NO3--N supply rate. The TS treatments supplied the highest rate of NH4 -N, followed by WDG compared to the other amendments. The WDG treatments were able to provide the greatest supply of PO4-3-P supply in comparison to the other amendments. Microbial N immobilization was associated with glycerol treatments applied alone. This study showed that the investigated biofuel by-products can be suitable soil amendments as a result of their ability to supply nutrients and N2O emissions that did not exceed that of the conventional urea fertilizer.

Key Words

Distillers grains; thin stillage; glycerol; carbon dioxide; nitrous oxide; nutrient supply rates