Permeable Synthetic Covers for Controlling Emissions from Liquid Dairy Manure

Abstract

Liquid manure storages emit greenhouse gases (GHGs) and ammonia (NH(3)), which can have negative effects in the atmosphere and ecosystems. Installing a floating cover on liquid manure storages is one approach for reducing emissions. In this study, a permeable synthetic cover (Biocap (TM)) was tested continuously for 165-d (undisturbed storage + 3-d agitation) in Nova Scotia, Canada. Covers were installed on three tanks of batch-loaded dairy manure (1.3 m depth x 6.6 m(2) each), while three identical tanks remained uncovered (controls). Fluxes were measured using steady-state chambers. Methane (CH(4)), carbon dioxide (CO(2)), and nitrous oxide 01)0) were measured by absorption spectroscopy, and NH(3) was measured using acid traps. Results showed covered tanks consistently reduced NH(3) fluxes by approximately 90%, even though a surface crust formed on controls after about 50 days. Covers continued to reduce NH(3) flux during agitation. Covered tanks also emitted significantly less CO(2) and N(2)O than the controls (p-value <0.01). However, CH(4) fluxes were not reduced, and therefore overall GHG fluxes were not substantially reduced. Short-term trends in CH(4), CO(2), and N(2)O flux provided insight into cover function. Notably, bubble fluxes were a key component of CH(4) emissions in both treatments, suggesting the covers did not impede CH(4) transport.