Karin Kauer

Summer cover crops can improve soil fertility and contribute to nitrogen (N) supply in temperate cropping systems, yet the effects of mixture composition and sowing timing remain insufficiently documented. This study evaluated biomass production and N accumulation of five multispecies cover crop mixtures grown in Estonia during 2024–2025 under two sowing dates per year. Aboveground biomass, botanical composition, and carbon (C) and nitrogen concentrations were measured to assess productivity, species contributions, and residue quality. Earlier sowing was generally associated with higher biomass and N accumulation, with first-sown mixtures producing, on average, 38.7% more biomass than later-sown mixtures. Mixture performance was strongly shaped by species composition and competitive hierarchies. Total N accumulation of the cover crop mixtures ranged from 42 to 275 kg N ha⁻¹ depending on mixture composition and sowing time, with mixtures dominated by common vetch (Vicia sativa L.) achieving the highest values. Oat (Avena sativa) dominated and contributed substantially to biomass in mixtures lacking competitive legumes, whereas sunflower (Helianthus annuus) and maize (Zea mays) performed less well under delayed sowing. Low-growing species such as Persian clover (Trifolium resupinatum) produced little biomass when grown with highly competitive species. Legumes exhibited lower C:N ratios than non-legumes, while mixture-level values remained moderate, suggesting residue quality with potential for favourable decomposition and nutrient release in summer cover crop systems under temperate conditions.

Soil organic carbon (SOC) comprises particulate (POC) and mineral-associated organic carbon (MAOC), which differ in formation, stabilization, and loss mechanisms. While the current global distribution of POC and MAOC is characterized, their vulnerability under future climate scenarios remains unclear. Using 3284 topsoil (0-30 cm) observations from six continents, we identify high-latitude soils as global hotspots of SOC vulnerability under shared socioeconomic pathway scenarios (SSP126, SSP245, and SSP585). Under a high-emission scenario (SSP585), high-latitude soils are projected to lose substantial POC by 2100, accounting for about 81 ± 10% of total SOC losses. These declines are driven by the high proportion of SOC stored as POC (f_POC) and its high temperature sensitivity. We show that f_POC is a robust indicator of SOC vulnerability to climate change. Globally, the projected POC decline corresponds to a cumulative carbon dioxide (CO₂) release of 81.34 Pg CO₂-equivalent by 2100, highlighting the importance of preserving POC to mitigate climate feedbacks.

Substantial progress has been made in estimating and mapping soil organic carbon stocks, but the quantification of carbon stock change rates still needs exploration in numerous soil and management combinations. In this research, the soil organic carbon (SOC) changes and soil organic matter (SOM) composition in the long-term experiment (established in 1989, Tartu, Estonia) with sandy loam soil were studied. The experiment involves three-field crop rotation (potato-spring wheat-spring barley) with two fertilization regimes: (1) mineral fertilisation (N rates 0, 40, 80, 120 and 160 kg ha-1) and (2) same mineral fertilisation treatments with farmyard manure amendment. During 1989–2017, every spring the soil samples were taken from the 0-20 cm soil layer, and SOC concentration was measured by dry combustion. In 2017, the size fractionation of soil samples was also performed. In 2022, the soil samples were also taken from the area surrounding the experimental site, which has not been cultivated since the experiment was established and has been as permanent grassland (GR). Soil mineral-associated organic matter (MAOM fraction;

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and a stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O emissions into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with an increased mineral N fertilisation rate. Crop type also has a significant impact on soil N₂O emissions. Higher N₂O emissions were attained with the application of manure in comparison to mineral fertilisation. Manure amendment also increased the number of N cycle genes that are significant in the variations of N₂O. The study indicates that N₂O emissions were mainly related to nitrification in the soil. Quantification of nitrogen cycle functional genes also showed the potential role of denitrification, comammox (complete ammonia oxidation) and dissimilatory nitrate reduction to ammonium (DNRA) processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. The results of the study provide evidence that, for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield and N₂O emissions and achieving a high NUE. Sorghum showed good potential for cultivation in temperate climates, as it showed a similar biomass yield compared to the other crop types and fertilisation rates but maintained low N₂O emissions and N losses in a mineral N fertilisation rate of 80 kg N ha⁻¹.

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.

Fertilised soils are a significant source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N₂O into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N₂O and N₂ emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N₂O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with increased mineral N fertilisation rate. Higher N₂O emissions were attained with the application of manure. Manure amendment also increased the number of N cycle genes that are significant in the change of N₂O. Contrary to our hypothesis, there was no significant influence of crop type on soil N₂O emissions. The study indicated dominance of nitrification over denitrification in the soil. Microbial analyses also showed the potential role of comammox and DNRA processes as a source of N₂O. Our study did not find soil moisture to be significantly linked to N₂O emissions. Results of the study provide evidence that for wheat, a fertilisation rate of 80 kg N ha⁻¹ is closest to the optimal rate for balancing biomass yield, N₂O emissions, and achieving high NUE. Sorghum showed potential for cultivation in temperate climate, as sorghum maintained low N₂O emissions and N losses on mineral N fertilisation rate of 80 kg N ha⁻¹.