Lignite effects on NH 3 , N 2 O, CO 2 and CH 4 emissions during composting of manure.

Production of compost from cattle manure results in ammonia (NH ₃ ) and greenhouse gas emissions, causing the loss of valuable nitrogen (N) and having negative environmental impacts. Lignite addition to cattle pens has been reported to reduce NH ₃ emissions from manure by approximately 60%. However, the effect of lignite additions during the manure composting process, in terms of gaseous emissions of NH ₃ , nitrous oxide (N ₂ O), carbon dioxide (CO ₂ ), and methane (CH ₄ ) is not clear. This composting study was conducted at a commercial cattle feedlot in Victoria, Australia. Prior to cattle entering the feedlot, we applied 4.5 kg m ^-2 of dry lignite to a treatment pen, and no lignite to a control pen. After 90 days of occupancy, the cattle were removed and the accumulated manure from each pen was used to form two separate compost windrows (control and treatment). During composting we collected manure samples regularly and quantified gaseous emissions of NH ₃ , N ₂ O, CO ₂ , and CH ₄ from both windrows with an inverse-dispersion technique using open-path Fourier transform infrared spectroscopy (OP-FTIR). Over the 87-day measurement period, the cumulative gas fluxes of NH ₃ , N ₂ O, CO ₂ , and CH ₄ were 3.4 (± 0.6, standard error), 0.4 (± 0.1), 932 (± 99), and 1.2 (± 0.3) g kg ^-1 (initial dry matter (DM)), respectively for the lignite amended windrow, and 7.2 (± 1.3), 0.1 (± 0.03), 579 (± 50) and -0.5 (± 0.1) g kg ^-1 DM, respectively for the non-lignite windrow. The addition of lignite reduced NH ₃ emissions by 54% during composting, but increased total greenhouse gas (GHG) emissions by 2.6 times. Total N losses as NH ₃ -N and N ₂ O-N were approximately 11 and 25% of initial N for the lignite and non-lignite windrows, respectively. The effectiveness of retaining N was obvious in the first three weeks after windrow formation. A cost-benefit analysis indicated that the benefit of lignite addition to cattle pens by reduced NH ₃ emission could justify the trade-off of increased GHG emissions.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)