Date of Award

2016

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Interdepartmental Program

First Advisor

José Amador

Abstract

Anthropogenic causes of rising levels of greenhouse gases (GHG) such as CO2, CH4, and N2O in the earth’s atmosphere are increasingly of concern due to their effects on climate change. Much of the earth’s carbon is retained in sinks created when atmospheric C is transformed into various forms of soil organic matter (SOM) and stored as stable, decay-resistant SOM for variable periods of time. When land is in its natural state, SOM is generally at a natural equilibrium of C inputs and outputs. Land use changes, particularly cultivation and conventional agricultural practices, have resulted in lower levels of SOM, leading to degraded, less productive soils. SOM is important to the physical, chemical and biological composition of the soil, and there has been a great deal of research addressing the impact of agricultural management practices on the retention of SOM and nutrients. One area of research is the use of organic waste materials as soil amendments to increase SOM. In addition to improving SOM, soil amendments also modify the physical, chemical, and biological properties of the soil, which affect the relative rates of production and consumption of GHG. The direct effects of the amendments are mediated by environmental factors that influence GHG flux, such as soil temperature and soil moisture. Organic wastes can be used as soil amendments either directly or after composting, providing an alternative to disposal in landfills or release into the environment as pollutants. The studies reported here examine the effects of residual waste materials (RWM) on GHG flux from agricultural soil. The amendments used included paper fiber with chicken manure (PF), dehydrated food waste (DFW), yard waste compost (YW), biosolids and yard waste compost (BIO), multisource compost (MC), and mineral fertilizer (MF). The first study measured GHG fluxes and assessed relationships between GHG fluxes and soil properties from a field, in Kingston, RI, sown in sweet corn during the 2014 growing season. During this study, DFW and PF produced significantly higher maximum CO2 fluxes than the control (CTL) (a field sown in buckwheat) in June. All other amended plots reached their maximum CO2 flux in August, but none where significantly different from the CTL. Measurements for CH4 and N2O did not follow a temporal pattern, and were not significantly different from the CTL. No soil properties were significantly correlated with the change in GHG flux from all soils, but CO2 and CH4 fluxes for CTL and MC, respectively, were significantly correlated with active C and N2O from PF with moisture content. The second study used microcosms to examine the effect of moisture and temperature on GHG flux and changes to soil properties in an amended agricultural soil. The flux values of CO2, CH4 and N2O were significantly affected by interactions between temperature, moisture and amendment. Dehydrated food waste had highest CO2 flux observed at 25°C and field capacity and consistently resulted in CO2 flux values higher than unamended soil (CTL) at most moisture-temperature combinations, while MF and YW were always had the lowest CO2 flux values. Net CH4 flux was not affected by moisture differences among treatments, except at saturation and 25°C. Nitrous oxide production was most responsive to moisture, regardless of temperature and amendment type. Most amendments did not result in significantly increased GHG flux relative to CTL, and in some instances resulted in decreased flux for CH4 and N2O at moisture contents and temperatures likely to be encountered in the field. The exception was DFW, which produced the largest flux of CO2 at 25°C, of N2O at 20°C saturation, and of CH4 at all moisture contents and temperatures. Overall, we found that the use of RWM as soil amendments affected the magnitude, direction and timing of GHG flux and responds to differences in temperature and moisture. Generally, RWM - except for DFW - did not cause increased GHG fluxes of concern.

Available for download on Saturday, March 31, 2018

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