Impact of slurry additives on nitrogen emissions, grass agronomy and soil microbial communities following slurry landspreading

This study assessed the effects of specific slurry additives on nitrous oxide (N 2 O) emissions, grass herbage yield and N uptake and soil microbial communities. The experimental work was conducted on two soil types: i) a moderately to poorly drained fine loam and ii) an imperfectly drained clay loam over two growing seasons. Cattle slurry was applied in three split applications at both sites simulating trailing shoe application method and the treatments were control (no treatment), unamended slurry, slurry + sulphuric acid, slurry + biochar, slurry + gypsum and urea + urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) (NBPT-urea). Nitrous oxide was measured during the growing period using the static chambers and dry matter yield was measured at every harvest. Ammonia (NH 3 ) was also quantified at one of the sites, therefore NH 3 responses are site-specific. Ammonia was measured within the first week of slurry application using dynamic chambers coupled with a photoacoustic gas analyser. Soil samples were collected after the end of the experiment for microbial analysis at both sites. The acidified slurry increased grass yield by more than one tonne ha −1 , increased plant N recovery by 21 to 24 kg N ha −1 , suggesting improved nitrogen conservation may have contributed to these agronomic benefits, and increased fungal abundance however, it also increased N 2 O on one occasion. The other slurry amendments did not have significant effect on N 2 O. The cumulative N 2 O emissions from the moderately drained soil were significantly lower than the imperfectly drained soil. None of the amendments significantly reduced NH 3 emissions in the moderately to poorly drained soil, while biochar increased NH 3 during a single application timing.