Response of Agricultural Soil Greenhouse Gas Fluxes to Amendment with Residual Waste Materials: Effects of Temperature and Moisture.

Soils play an integral part in global carbon (C) cycling by sequestering C as soil organic matter (SOM). Human activities, like converting forests to agriculture, have increased the rate of SOM decomposition, and thus the release of C as CO₂ and CH₄ into the atmosphere. To counteract loss of SOM in agricultural soils, soil can be amended with residual waste materials, like biosolids and compost. These materials add C and N to the soil, affecting physical, chemical, and biological properties and processes. This, coupled with variations in temperature and moisture, results in change to the flux of C and N-containing greenhouse gases (GHGs) from soil. We used microcosms to investigate the magnitude of GHG (CO₂, CH₄, N₂O) flux as a function of soil temperature and moisture in an agricultural soil amended with residual waste materials. Soil moisture was adjusted to permanent wilting point, field capacity or saturation and amended with 10 Mg total C ha^-1 in the form of paper fiber with chicken manure (PF), dehydrated food waste (DFW), yard waste compost (YW), biosolids and yard waste compost (BIO), multisource compost (MC), or 560 kg ha^-1 of mineral fertilizer (MF). Our control (CTRL) was un-amended soil. Microcosms were incubated at 10, 15, 20, or 25°C and gas concentrations determined over 14 days. The highest CO₂ production was observed at 25°C and field capacity, with production following the order: DFW>MC>CTRL>PF>MF>BIO>YW. When compared to the CTRL, CO₂ production from DFW was higher at most moisture-temperature combinations, while MF and YW were always lowest. Contrary to our prediction, CO₂ production was not related to levels of active C in the amendments. Net CH₄ production/consumption was not affected by moisture differences among treatments, but varied in response to temperature and amendment. Nitrous oxide production was most responsive to moisture, regardless temperature and amendment type.