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The application of organic materials to soil can recycle nutrients and increase organic matter in agricultural lands. Digestate can be used as a nutrient source for crop production but it has also been shown to stimulate greenhouse gas (GHG) emissions from amended soils. While edaphic factors, such as soil texture and pH, have been shown to be strong determinants of soil GHG fluxes, the impact of the legacy of previous management practices is less well understood. Here we aim to investigate the impact of such legacy effects and to contrast them against soil properties to identify the key determinants of soil GHG fluxes following digestate application. Soil from an already established field experiment was used to set up a pot experiment, to evaluate N2O, CH4 and CO2 fluxes from cattle‐slurry‐digestate amended soils. The soil had been treated with farmyard manure, green manure or synthetic N‐fertilizer, 18 months before the pot experiment was set up. Following homogenization and a preincubation stage, digestate was added at a concentration of 250 kg total N/ha eq. Soil GHG fluxes were then sampled over a 64 day period. The digestate stimulated emissions of the three GHGs compared to controls. The legacy of previous soil management was found to be a key determinant of CO2 and N2O flux while edaphic variables did not have a significant effect across the range of variables included in this experiment. Conversely, edaphic variables, in particular texture, were the main determinant of CH4 flux from soil following digestate application. Results demonstrate that edaphic factors and current soil management regime alone are not effective predictors of soil GHG flux response following digestate application. Knowledge of the site management in terms of organic amendments is required to make robust predictions of the likely soil GHG flux response following digestate application to soil. [ABSTRACT FROM AUTHOR]

Bacteria and fungi have been shown to produce nitrous oxide (N 2 O) during denitrification, but their contribution after nitrate (NO 3 −) application to soil is not clearly established. In a microcosm experiment, the relative contribution of bacteria and fungi to N 2 O and carbon dioxide (CO 2) production by four contrasting soils representing different land uses after KNO 3 addition was studied. The soils were daily wetted to 80% water-filled pore space (WFPS) and kept under greenhouse conditions for 10 days. The fungicide cycloheximide and the bactericide streptomycin were used to determine the possible microbial origin of the N 2 O and CO 2 emissions. Non-target effects of the antibiotics on the emission of N 2 O and CO 2 were evaluated using the inhibitor additivity ratio (IAR). The abundance of the bacterial and fungal communities was estimated by quantitative PCR (qPCR) of the bacterial 16S rRNA gene and the fungal internal transcribed spacer (ITS) region, respectively. The gene copy number of bacterial denitrifiers was calculated after quantification of the nirK , nirS , norB , nosZ I and nosZ II genes. After 10 d, regardless of the soil type, the cumulative N 2 O emission from the soils treated with cycloheximide or streptomycin were similar. In all the four soils, N 2 O fluxes were greater (on average 1.8 ± 0.3 times) in soils amended with the fungicide than with the bactericide during incubation for the first 48–96 h. Greater N 2 O emissions (on average 1.7 ± 0.2 times) were detected in soils where bacteria were inhibited in comparison to those treated with the fungicide from 96 to 240 h. On average, 68.5% of the total CO 2 emitted during the 10-d incubation period was produced in soils treated with the fungicide and 31.5% in those treated with the bactericide. The greater contribution of bacteria to the production of N 2 O than fungi during the first 48–96 h was possibly due to a faster used of nitrate. Variations in the abundance of bacterial 16S rRNA genes, the ITS region, and the nirK , nirS , norB and nosZ I bacterial denitrification genes indicated that the antibiotics used to prevent the growth of bacteria and fungi were effective during incubation. These results suggest that both bacteria and fungi should be considered when designing and applying greenhouse gas mitigation strategies in soils and that their relative contribution to produce N 2 O and CO 2 can vary with time and nitrate availability. • In a 10-d microcosm experiment, bacteria dominated fungi for N 2 O emissions during the first 3 d after N-fertilisation. • Fungi dominated bacteria for N 2 O emissions during the remaining 7-d of treatment. • After 10-d, bacteria and fungi similarly contributed to N 2 O production in the four soils analysed. • Bacteria were greater CO 2 producers than fungi after the 10-d treatment in the four soils analysed. • Bacteria and fungi should be considered when designing greenhouse gas mitigation strategies. [ABSTRACT FROM AUTHOR]