DIGESTATES FROM FOOD WASTE AND LIGNOCELLULOSIC MATERIALS: EFFECTS ON PLANT GROWTH
Date
2019
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Abstract
Anaerobic digestion is a process that converts organic matter into two useful products: biogas, which can be used for energy, and digestate, which has potential as a fertilizer and soil amendment. The majority of research on digestates focuses on their fertilizer value. However, there is a lack of information about other effects they may have on plant growth, both positive and negative. Understanding the effects of digestates on plant growth is essential to optimizing their use in agriculture, and helping to close the loop of energy production. A series of experiments were conducted to assess the potential presence and activity of phytohormone-like compounds in a food waste digestate (FWD) and a lignocellulosic digestate (LCD). In preliminary laboratory experiments, bioassays suggested that there may be hormone-like activity. Further research would be needed to determine the active compounds responsible for these effects. In addition, a greenhouse experiment was conducted to test the effects of digestates in comparison with a synthetic nutrient solution made to mimic their mineral and nutrient content. Both the FWD and the LCD increased plant growth significantly more than their synthetic nutrient equivalents and showed a quadratic-like response to increasing rates of digestates in early growth of Brassica juncea. A second greenhouse study evaluated the effects of digestates, mineral fertilizers and combinations of the two on plant biomass, root growth and nutrient use of Brassica juncea plants. Combinations of LCD and mineral fertilizer performed as well or slightly better than the fertilizer control for most parameters, including aboveground biomass and root length. These same combinations had significantly higher nitrogen use efficiency than the fertilizer control. There were inhibitory effects observed with pure LCD treatments, likely due to the high EC of the media from digestate application. Based on this research, LCD could partially replace mineral fertilizers for Brassica juncea at up to 50% of the target nitrogen rate and may lead to increased plant growth beyond mineral fertilizers. FWD could replace up to 100% of the target nitrogen application without causing significant negative effects on plant growth. Further research is needed both to verify these findings under field conditions and with different species of plants to determine optimum rates of application.
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Soil sciences, Agriculture, anaerobic digestion, digestate, fertilizer
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101 pages
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