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UBC Theses and Dissertations

Soil amendments from urban residuals and their effect on crop productivity and nutrient cycling Bazza, Zineb


Urban residuals have been used in agriculture to decrease disposal costs, recycle nutrients, and prevent or counteract the degradation of soils linked to the intensification of agriculture. Technological advancements continue to produce novel residuals that can be used as soil amendments, with the potential to reduce or eliminate waste. This thesis entails two studies that examine the potential to utilize new urban residuals for food production. The objectives of the first study were to look at the potential benefits and impacts, on crop productivity and nutrient cycling, of using monopotassium phosphate (MKP) fertilizers, made using the co-products of biodiesel production. The treatments in this study include MKP-M, a purified form of MKP, MKP-C, a crude MKP from biodiesel production with glycerin and MKP-C2, similar to MKP-C but with double the glycerin. There were no differences in yields in the field trial. The greenhouse trial showed higher pepper yields using MKP-C and foliar MKP-M, and higher number of fruits with foliar MKP-M and a retail MKP. Soil analyses suggest that glycerin in certain amounts can inhibit nitrification and improve nitrogen (N) uptake. In the second study, a compost like material (HTI Compost) made in 24 hours was tested to better understand the effects unstable and immature compost could have on yield, nutrient cycling and greenhouse gas (GHG) emissions. The treatments were the HTI compost, UBC farm compost (typical municipal compost), a mix of the two composts, HTI compost + bloodmeal, and no amendment. The results show the HTI treatments had similar yields to the UBC farm compost for beets, but lower yields in spinach due to reduced or delayed germination. The HTI treatments delayed soil N availability and resulted in higher GHG emissions. Emissions of carbon dioxide and methane from the HTI treatments were high in the beginning of the season when the compost was decomposing, while nitrous oxide emissions were highest later on as decomposition rates declined. These results show promising benefits for using urban residuals as soil amendments, but the management of these amendments is crucial to avoid any negative impacts on crop productivity or the environment.

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