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Cattle and cow slurry storage is a significant source of agricultural greenhouse gas (GHG) and ammonia (NH3) emissions. While acidification has been demonstrated to significantly reduce these emissions, a knowledge gap exists to identify a range of chemical amendments that are safe, suitable and cost effective to mitigate both GHG and NH 3 gases simultaneously. The current study showed that ferric chloride, sulphuric acid, alum and acetic acid were extremely effective at abating emissions, with NH 3 reduced by 96%, 85%, 82% and 73%, respectively. In terms of methane (CH 4), ferric chloride, alum, sulphuric acid and acetic acid reduced emissions by 98%, 96%, 95% and 94%, respectively. Previous studies have found that the reduction of >pH 6 can inhibit the release of these gases; however, the effectiveness can vary depending on each amendment's composition. The cost benefit analysis, assessed the amendments in terms of both gaseous emissions reduction and net cost. Sulphuric acid, acetic acid, ferric chloride and alum ranked best, respectively. Currently, the cost of implementing these amendments is, at best, cost neutral. Therefore, incentivising chemical amendments for the abatement of GHG and NH 3 gases from slurry storage is needed. This incubation experiment is an effective means of pre-screening amendments before they are explored at pilot or full scale with subsequent field application. Future research should consider the assessment of cheaper on- and off-farm alternative waste streams as slurry amendment. Image 1 • Acidification of cattle and dairy slurry was investigated. • Target pH of 5.5 resulted in a 96% reduction in NH 3 and 98% reduction in CH 4. • Ferric chloride reductions were independent of pH value. • Cost analysis revealed financial incentives are needed for scaled implementation. [ABSTRACT FROM AUTHOR]

Highlights • We measured soil nitrous oxide flux, methane flux and soil respiration followiing driange installation. • We measuered water filled pore space (WFPS), soil mineral nitrogen (N), herbage N uptake, soil organic carbon (SOC) and soil total nitrogen (TN) following the installation of mole and gravel mole drainage systems in a clay-loam soil in two experiments over 36 months. • Drainage treatment deepened the water table and decreased WFPS. • Mole and gravel mole drainage had no impact on soil GHG fluxes, soil N mineralisation, soil N nitrification, SOC and TN. Abstract Shallow drainage (e.g. mole and gravel mole drainage installed at 0.55 m below soil surface) is used on pasture-based farms to reduce soil moisture, deepen water table depth and thus increase grass utilization on soils with impeded drainage. There is, however, a lack of research on the effect that these drainage techniques have on soil greenhouse gas (GHG) emissions. Hence the objective of this study was to investigate the effects of mole and gravel mole drainage on soil GHG fluxes. Soil nitrous oxide (N 2 O), soil root respiration (CO 2) and soil methane (CH 4) fluxes were measured in two experiments conducted over a 36 month period. The experiments were conducted on permanent grassland with impeded drainage on a eutric gleysol (humic) in Ireland (52°30′N, 08°12′W). Both experiments were arranged in randomized complete block design. There were three treatments: (i) undrained control, (ii) mole drainage and (iii) gravel mole drainage. Soil GHG fluxes, soil water filled pore space (WFPS) and soil temperature were measured on a weekly basis and soil mineral nitrogen (N), herbage N uptake, soil organic carbon (SOC) and soil total N (TN) were measured seasonally and annually over the sampling period. Drainage treatments (P < 0.05) deepened (mean ± SE) the water table by 0.17±0.03 m and decreased WFPS by 7±0.2%. However no (P > 0.05) impact of drainage treatment was detected on soil average daily GHG fluxes (9.84±6.34g N 2 O-N ha−1day−1, 34.05 ± 12.90 kg CO 2 -C ha−1day−1 and −0.91 ± 3.70 g CH 4 -C ha-1day-1), soil N mineralisation, soil N nitrification, SOC and TN in both experiments. The results indicate that mole and gravel mole drainage can be installed on farms with similar management and soil type to that described in the present study without impact on the soil GHG emissions. [ABSTRACT FROM AUTHOR]

The production of bovine slurry and its subsequent storage are significant sources of ammonia (NH 3) and greenhouse gases (GHGs). Chemical acidification of manures has been shown to significantly reduce these emissions. Waste products, derived from food processing and on-farm practices, may be used as "natural" acidifiers. However, the efficacy of these products in reducing pH and any subsequent emissions are unknown. Commercial "slurry improvers" or "additives" may also be a viable mitigation option; however, their effectiveness is questionable. This study investigated the efficacy and cost of a range of waste and commercial amendments and a chemical acidifier, ferric chloride (FeCl 3), to identify the most effective amendment for NH 3 and GHG emissions reduction. Ammonia abatement potential was observed for 5% sugar beet molasses (67% reduction), 7% apple pulp (49% reduction), and 7% grass silage (38% reduction). Methane (CH 4) emissions were reduced only by spent brewers' grain, sugarbeet molasses, and grass silage effluent at the higher inclusions (i.e. amounts added), with reductions ranging from 15% to 70%. Carbon dioxide (CO 2) emissions were significantly increased with the addition of waste amendments. Commercially available additives had little impact on emissions, with the exception of one treatment, which reduced CH 4 by approximately 10%. Ferric chloride reduced NH 3 emissions by 20%–68%, CH 4 by 6%–65%, and CO 2 by 6%–38%, depending on the inclusion. All waste amendments had low marginal abatement costs ranging from -€0.46 to €0.88 kg−1 NH 3 abated compared to FeCl 3 and commercial amendments (€1.80 to €231 kg−1 NH 3). This incubation experiment demonstrated that a range of on-farm and industry waste streams could be valorised to reduce NH 3 emissions. However, many of these may result in higher CH 4 and CO 2 emissions due to input of labile carbon sources. Therefore, based on the results of the current study, it is recommended that sugarbeet molasses and ferric chloride, at 5% and 1.1% inclusions respectively, be examined in field experiments. [Display omitted] • Farm waste products may be used to reduce NH 3 and GHG emissions. • Ferric chloride and sugarbeet molasses reduced emissions. • A cost saving of ∼ €0.46 kg−1 NH 3 was achieved using waste amendments. • Commercial products were ineffective in abating NH 3 and GHG emissions. [ABSTRACT FROM AUTHOR]