Greenhouse gas emissions, nitrogen dynamics and barley productivity as impacted by biosolids applications

Land application of biosolids is recognized as a sustainable disposal approach, as it enables the recycling of nutrients that can be used by plants. However, the emissions of greenhouse gases (GHG) from such a practice is an environmental concern that needs to be addressed. We evaluated the fluxes of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2); soil available N; barley (Hordeum vulgare L.) for silage biomass productivity; and N use efficiency (NUE) as a function of the application of three contrasting types of biosolids (mesophilic anaerobic digested [BM], composted [BC], and alkaline-stabilized [BA]) and granular urea in Central Alberta, Canada, over two experimental years. The combination of each biosolid with urea was also evaluated. All N source treatments were assessed with both surface (S) and incorporation (I) placements. Concurrent increases in soil moisture and available N triggered high N2O emissions during the growing season and spring thaw. Emissions during thawing accounted for 42% of the total annual cumulative. Incorporation of the N source increased N2O emissions by at least 22% compared with surface-applied N. In general, CO2 fluxes followed similar patterns to the N2O fluxes, whereas CH4 fluxes were minimal. Overall, BMI showed the highest N2O, CO2, and CH4 emissions. On the basis of field fluxes, annual N2O emission factor (EFarea) from urea-amended soils (0.62 ± 0.14%) were fivefold higher than those from soils receiving only BA or BC (0.12 ± 0.04% or 0.12 ± 0.03%, respectively, P < 0.05), but EFarea from soils amended with only BM (1.33 ± 034%) was more than double the EFarea from urea-amended soils (P > 0.05). We calculated a partial GHG balance in which field N2O emissions were the main contributor, accounting for up to 96% of the budget. The GHG footprint of urea manufacturing also made a considerable contribution to the GHG balance (up to 49%), which offset the comparatively low field N2O emissions from the urea-amended fields, leading to CO2 equivalents even higher than the BA- and BC-amended fields. Incorporating the N sources enhanced barley biomass by 12% based on the 2-year mean. In certain cases, the combination of biosolids and urea (e.g., BMURI, BMURS, BCURS) showed even higher biomass and NUE, as well as lower N2O emissions. Our findings will help to improve predictions and mitigation strategies for GHG emissions, particularly for N2O, from agricultural soils receiving biosolids applications.