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Land application of cattle slurry can result in incidental and chronic phosphorus (P) loss to waterbodies, leading to eutrophication. Chemical amendment of slurry has been proposed as a management practice, allowing slurry nutrients to remain available to plants whilst mitigating P losses in runoff. The effectiveness of amendments is well understood but their impacts on other loss pathways (so-called 'pollution swapping' potential) and therefore the feasibility of using such amendments has not been examined to date. The aim of this laboratory scale study was to determine how the chemical amendment of slurry affects losses of NH3, CH4, N2O, and CO2. Alum, FeCl2, Polyaluminium chloride (PAC)- and biochar reduced NH3 emissions by 92, 54, 65 and 77% compared to the slurry control, while lime increased emissions by 114%. Cumulative N2O emissions of cattle slurry increased when amended with alum and FeCl2 by 202% and 154% compared to the slurry only treatment. Lime, PAC and biochar resulted in a reduction of 44, 29 and 63% in cumulative N2O loss compared to the slurry only treatment. Addition of amendments to slurry did not significantly affect soil CO2 release during the study while CH4 emissions followed a similar trend for all of the amended slurries applied, with an initial increase in losses followed by a rapid decrease for the duration of the study. All of the amendments examined reduced the initial peak in CH4 emissions compared to the slurry only treatment. There was no significant effect of slurry amendments on global warming potential (GWP) caused by slurry land application, with the exception of biochar. After considering pollution swapping in conjunction with amendment effectiveness, the amendments recommended for further field study are PAC, alum and lime. This study has also shown that biochar has potential to reduce GHG losses arising from slurry application.

The effects of slurry application method and weather conditions after application on ammonia volatilisation are well documented, however, the effect on slurry N recovery in herbage is less evident due to large variability of results. The objective of this field experiment was to determine the recovery of cattle slurry NH4-N in herbage and soil in the year of application as affected by application method (trailing shoe versus broadcast) and season of application (spring versus summer), using 15N as a tracer. In 2007 and 2008, 15N enriched slurry was applied on grassland plots. N recovery in herbage and soil during the year of application was determined. Both spring and trailing shoe application resulted in significantly higher herbage DM yields, N uptake and an increased recovery of 15NH4-N in herbage. Additionally, the recovery of slurry 15NH4-N in the soil at the end of the growing season was increased. Spring and trailing shoe application reduced the losses of slurry 15NH4-N by on average 14 and 18 percentage points, respectively, which corresponded closely to ammonia volatilisation as predicted by the ALFAM model. It was concluded that slurry N recovery in temperate pasture systems can be increased by adjusting the slurry application method or timing. [ABSTRACT FROM AUTHOR]

Livestock excreta deposition on concrete farmyards has been identified as an important source of ammonia (NH 3) emissions from agriculture. The objective of this study was to quantify the effect of urine application rate and four cleaning strategies on NH 3 emissions from excreta deposited on a concrete yard. Three experiments were conducted on a concrete yard over a three week period in August 2016. Experiment 1 consisted of 1 kg dung applied with either (i) 0.67 l urine (1:0.67), (ii) 1 l urine (1:1) or (iii) 2 l urine (1:2). In experiments 2 and 3 the treatments were (i) non cleaned control, (ii) cleaned after 1 h and (iii) cleaned after 3 h. The cleaning method in experiment 2 and 3 was pressure washing and scraping, respectively. Ammonia emissions were measured using wind-tunnels for 72 h. Cumulative NH 3 emissions increased linearly with increasing urine N rate and emission factors ranged from 46% to 67% of urine urea-N applied and from 22% to 29% of total N applied. In experiment 2 and 3 the greatest reduction in cumulative NH 3 emissions was obtained from pressure washing at 1 h which reduced emissions compared to the non-cleaned control by 91%. Pressure washing at 3 h reduced emissions by 80% while scraping after 1 h and 3 h reduced emissions by 78% and 54%, respectively. Farmers should be encouraged to clean their animal handling yards as soon as possible after use in order to maximise reductions in NH 3 emissions from this source. Image 1 • Three experiments measuring NH 3 using wind tunnels from a concrete farmyard. • NH 3 emissions increased linearly with increasing cow urine application rate. • Pressure washing was more effective at reducing NH 3 emissions than scraping. • Interval between excreta deposition and farmyard cleaning is important for NH 3 reduction. [ABSTRACT FROM AUTHOR]