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The atmospheric increase in N 2 O is mainly derived from N fertilisation in agriculture, and improved emission estimates are needed for effective mitigation. This study presents first estimates of country-specific N 2 O emissions from synthetic and liquid organic fertilisers in Denmark. Representative crop rotations were established in four locations across Denmark to provide a realistic context for the estimation of N 2 O emissions, i.e., a dairy farm rotation in Western Denmark, dairy and pig farm rotations in Southwestern Denmark, and an arable rotation in Eastern Denmark. The four sites were light-textured and typical for Northern Europe, whereas rainfall varied considerably among sites and years. A randomised block design was used, and all crops were represented in triplicate each year with monitoring of N 2 O emissions between April 2020 and March 2022. Spring barley was part of all rotations, and here three synthetic fertilisers (NS, NPK and urea ammonium nitrate) and eight organic fertilisers (three cattle slurries, three pig slurries and two digestates) were applied in 1 m2 plots at either two or four sites in order to compare N 2 O emissions from the same N fertiliser materials under contrasting site conditions. Identical methodologies for management, fertiliser application, and N 2 O measurement and flux calculation, were used at all sites to ensure comparability. Manually operated chambers were used for N 2 O flux measurements. The continuous monitoring indicated a strong seasonal pattern across all four sites with the main part of N 2 O emissions during spring. The side-by-side comparison of several N sources at four sites in two years showed for synthetic fertilisers an average N 2 O emission factor for the spring period of 0.15% (95% C.I. −0.17 to 0.37%, n = 16), and for liquid organic fertilisers (pig and cattly slurries, and digestates) an average of 1.02% (95% C.I. 0.75 – 1.30%, n = 44). The higher N 2 O emissions from organic fertilisers, which was significant at each of the four sites, is in opposition to new N 2 O emission factors recently proposed in a refinement of the IPCC methodology for national inventories. The conflicting results are discussed with reference to region-specific site conditions and fertiliser types, and in particular the predominance of soils with a low clay content, and of liquid manure management, may explain the deviations from global estimates. A comparison of annual and spring N 2 O emissions indicated a difference in the order of 0.1 – 0.2% of the N input (n = 8), and the feasibility of estimating N 2 O emission factors based on emissions during the growing season only is discussed. • Annual N 2 O emissions from synthetic and organic fertilisers occurred mainly during spring. • Spring N 2 O emissions from the same fertilisers differed between locations and years. • Much higher N 2 O emissions were observed with organic than with synthetic N. • Sandy soils and liquid manure management may explain deviations from IPCC estimates. • Region- and system-specific N 2 O emission factors may significantly reduce uncertainties. [ABSTRACT FROM AUTHOR]

• Manure rate had little influence on the improvement of soil physical properties. • Improvement in soil gas transport and Ksat by manure varied with soil and crop type. • Silty soil had better improvements by manure addition than sandy and clayey soil. Manure application and crop rotation are common agricultural practices that can alter soil physical properties and affect soil functions. In this study, we assessed the effect of long-term manure fertilization (24 to 126 years) and crop type on soil hydraulic, aggregate and pore structural properties. Samples were collected from three long-term experiments (LTEs) in Sweden (silty clay, SiC), Germany (silt loam, SiL) and Denmark (sandy loam, SL). Measurements included water retention, air permeability and gas diffusivity measured at five matric potentials −3, −5, −10, −30 and −50 kPa, saturated hydraulic conductivity (K sat), bulk density (ρ b), and water-stable aggregates (WSA). The treatments at the three LTEs included various manure rates and crop sequences (winter wheat, maize, spring barley, and grass/clover). Results showed that long-term manure addition reduced ρ b by an average of 3–6% for all three sites, and improved soil water retention, plant available water and WSA for most investigated plots. However, increasing manure rates for the SiL and SL sites did not result in further improvements in soil water retention, ρ b and water-stable aggregates. The effect of manure on soil pore size distribution, gas transport, and K sat varied with soil and crop type. Manure increased the porosity of pores < 30 µm in the two fine-textured sites and increased the porosity of pores > 30 µm for wheat and maize plots in the SL site. Manure improved gas transport and K sat in the wheat plots and decreased these properties in the barley plots regardless of soil texture. The maize plots in the SL site had well developed pore structure, while the pore structure in the SiL site was relatively poor. Grass plots had poorer gas transport than maize plots in the SL site despite the manure addition. The study shows that improvements in soil physical and chemical properties arising from manure application largely depend on the crops grown and the soil texture. [ABSTRACT FROM AUTHOR]

• Depth specific EC estimates were used for mapping soil heterogeneities. • Including clay-rich zones improved the observed shallow groundwater levels. • The heterogeneous soil model better simulates the spatial hydraulic heads distribution. • The homogeneous and heterogeneous soil models simulated comparable tile drain flow. In agricultural fields, tile drains represent potential pathways for the migration of solutes, such as nitrates, in groundwater and surface water bodies. Tile drain flow is controlled by the temporal and spatial dynamics of the shallow groundwater table, which results from complex interactions between climate, topography and soil heterogeneity. Studies on the effect of topsoil heterogeneity on shallow water and drainage dynamics by fully 3D surface water and groundwater flow modeling are limited. The objective of our study is to demonstrate the use of depth specific electrical conductivity (EC) estimates to improve hydrological simulations in a tile-drained field. The model was applied to a field site in Denmark where times series of drainage discharge and water table elevations are available. Clay-rich soil zones were identified in a tile-drained field using depth specific electrical conductivity estimates generated by the inversion of apparent electrical conductivity data measured using an electromagnetic induction instrument. One model that included the low-permeability clayey zones in the soil layers down to a depth of 1.2 m was compared to a simpler model that assumed homogeneous soil layers. Both models simulate drainage discharge that compares well to the observations. However, including the clayey zones improves the simulation of hydraulic heads, and water table fluctuations, and generates flooded areas that are more representative of those observed during the wet seasons. Our results suggest that the simulation of water table fluctuations can be improved when the soil heterogeneity determined from depth specific EC estimates is included in integrated hydrological models. A better representation of the subsurface flow dynamics will also improve subsequent simulations of the transport and fate of agrochemical substances leaching from fields such as nitrate, which may deteriorate the quality of groundwater and surface water bodies. [ABSTRACT FROM AUTHOR]