Evaluating the Effects of Organic Amendment Applications on Nitrous Oxide Emissions From Salt-Affected Soils

Soil salinization and greenhouse gas emissions are major global environmental concerns. The extent of salinization and associated negative effects on soils and crop yields make the reclamation of these soils an international priority. With increasing interest in the use of organic amendments for remediating salt-affected soils, it is important to investigate their interactive effects on soil biogeochemical processes including greenhouse gas emissions, particularly carbon dioxide (CO2) and nitrous oxide (N2O). The objectives of this dissertation are to: 1) evaluate the effects of soil salinity, temperature, and carbon availability from organic amendments on CO2, N2O, and N2 emissions; 2) determine the effect of changes in salinity and temperature on soil mineral N concentration from salt-affected soils following organic amendment applications; and 3) determine whether CO2 and N2O emissions under field conditions were comparable qualitatively to those observed in the laboratory incubation studies. Organic amendments used in this research included: active greenwaste (AGW), cured greenwaste compost (CGW), active dairy manure (ADM), and cured dairy manure compost (CDM). The methods used in this research included monitoring CO2 and N2O emissions, estimating N2 emissions using acetylene block technique, and analysis of soil mineral N concentrations in the laboratory and field studies. Results from laboratory incubations showed that increases in soil salinity enhanced cumulative N2O-N losses but decreased cumulative CO2-C and N2 emissions and N2 to N2O-N ratios. Increases in soil temperatures greatly enhanced cumulative CO2-C, N2O-N, and N2 emissions and ratios of N2 to N2O-N from all treatments. In the field, results validated the laboratory findings that active organic materials, particularly AGW, reduced N2O emissions compared to cured amendments. In general, dairy manure amendments produced higher N2O emissions relative to the greenwaste treatments. In both laboratory and field studies, soils amended with greenwaste materials had lower soil nitrate concentrations compared to those treated with dairy manure amendments. Overall, this work showed that soil salinization resulted in greater N2O emissions following organic amendment applications. Nitrous oxide emissions are dependent on climatic conditions (e.g., precipitation and temperature), soil properties (e.g., electrical conductivity, microbial respiration, and nitrate concentration), organic amendment properties (e.g., feedstock and processing stage), and their interactions