Maintaining soil health is essential to ensuring an adequate food supply and preserving the environment. Insights from multiple stakeholder inquiries can provide a more nuanced understanding of conditions for soil health to support the adoption of sustainable soil management practices to meet national and regional goals. This article aimed to gather insights from stakeholders' perceptions of soil health and the state of soil knowledge in Denmark. Seven stakeholder inquiries, collected through a series of recent European soil research activities, were synthesised to identify perceptions of soil health, concerns about soil challenges and needs for harmonising production and use of knowledge related to sustainable soil management. Each inquiry was analysed individually, and common themes were discussed across topics. The data showed that the ecosystem service framework related to soil health was not evenly familiar across stakeholder categories. Identified concerns for soil health included climate change effects, knowledge transfer, economic pressure/risk, and soil challenges. The top ‘priority’ soil challenges identified were improving soil organic matter/peat soil, avoiding soil compaction and improving nutrient retention/use efficiency. Soil knowledge gaps related to soil challenges included: multidisciplinary and interdisciplinary long‐term experiments, site‐specific measures, science–policy–stakeholder interactions and knowledge feasibility at the farm level. Identified barriers preventing wider adoption of sustainable management practices included farm applicability of practices, farmers' engagement, knowledge sharing and lack of regulations for challenges such as soil compaction. Farmers were also concerned about the time and effort required to learn new practices, especially as it relates to their work/life balance and the challenge of implementing sustainable practices on commercial farms while ensuring profitability. These concerns might partially arise from knowledge gaps between stakeholder categories. Raising awareness of sustainable practices and addressing current and future risks such as pests and weather extremes are crucial for policy and stakeholder engagement.

Catch crops are an effective method for reducing nitrogen (N) leaching in agriculture, but the mineralization of incorporated catch crop residue N is difficult to predict and model. We conducted a five-month incubation experiment using fresh residue from three catch crops (hairy vetch, fodder radish and ryegrass) with three temperature treatments (2 °C, 15 °C and 2–15 °C variable temperature) and two termination methods (glyphosate and untreated). Mineral N (ammonium and nitrate) in soil was quantified at 0, 1, 2, 4, 8 and 20 weeks of incubation. Ammonium accumulation from residue decomposition showed a lag at low and variable temperature, but subsequent nitrification of the ammonium did not. Mineral N accumulation over time changed from exponential to sigmoidal mode at low and variable temperature. Incubation temperature significantly affected mineralization rates in a first-order kinetics (FOK) model, while plant type and termination method did not. Plant type alone had a significant effect on the final mineralized fraction of added catch crop N. FOK models modified to accommodate an initial lag were fitted to the incubation results and produced better goodness-of-fit statistics than simple FOK. We suggest that initial lags in residue decomposition should be investigated for the benefit of mineralization predictions in cropping models.

Denitrifying woodchip bioreactors (WBRs) remove nitrate ( ${\mathrm{NO}}_3^{-}$) from agricultural drainage water at field-scale, but their efficacy at cold temperatures remains uncertain. This study shows how hydraulic residence time (HRT) controls ${\mathrm{NO}}_3^{-}$ removal and environmental side-effects of WBRs at low water temperature under pilot-scale conditions with controlled operation of nine WBRs (94 dm³). Hydraulic properties were assessed by a bromide tracer test, and ${\mathrm{NO}}_3^{-}$ removal, emissions of nitrous oxide (N₂O) and methane (CH₄), and losses of dissolved organic carbon (DOC) were measured at HRTs of 5–30 h. Inlet ${\mathrm{NO}}_3^{-}$ concentrations were increasingly reduced at higher HRTs. The relationship between HRT and the efficiency (%) of ${\mathrm{NO}}_3^{-}$ removal was linear ( $R_{adj}^2$ = 0.94), while the relationship between HRT and ${\mathrm{NO}}_3^{-}$ reduction rates (NRR) was logistic ( $R_{adj}^2$ = 0.88). Gaseous emissions of N₂O were equally low at HRTs of 10–30 h, but higher at 5 h (P < 0.05). Methane fluxes were small, but with consistent emissions at HRTs of 20–30 h and uptake at 5–15 h. HRT had limited effect on effluent DOC concentrations, but strong effect on mass losses that were five-fold higher (320 mg L⁻¹) at the HRT of 5 h than at 30 h. In summary, at cold temperatures HRTs of ≤ 20 h resulted in suboptimal NRR, accelerating DOC losses, and increased risk of N₂O losses at least below a threshold HRT of 5–10 h. HRTs of 20–30 h gave maximal NRR, smallest losses of DOC and N₂O, but an increased risk of CH₄ emissions. GRAPHICAL ABSTRACT

Keeping cover crops to reduce nitrogen leaching often conflicts with timing tillage operations before the soil becomes un-trafficable during winter, while leaving cover crops in the field until spring raises concerns over pre-emptive competition with the following crop. Therefore, farmers may resort to tilling their fields in autumn after letting cover crops remain in the fields for only a short period of time. We explore the effects of this practice in a laboratory lysimeter setting by analyzing the leaching of nitrate from intact topsoil cores. Cores were extracted from no-till (NT) plots and plots tilled in autumn (AuT), in areas kept bare (B) and with volunteer winter rye plant cover (V) after harvest. Nitrate breakthrough curves show that V significantly reduced N leaching by 61% relative to B in NT, but did not have a significant effect in AuT. Dissection of leached cores and undisturbed reference cores indicated a significant removal of mineral N from the soil during the lysimeter experiment for all treatments except V in NT. This indicates that volunteer cover removed a crucial amount of leachable N and suggests that tillage counteracted the effect of V in AuT, likely due to a combination of reduced uptake and re-mineralization of N in cover crop residue.