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It is estimated that only 20% of fertilizers applied annually in the European agricultural systems are converted to finished products for human consumption. These low efficiencies result in large loss of nutrients into the environment with severe negative influences on soils, water and air, and constitute unacceptable health and environmental costs. In addition, around 45% of soils in the European countries have less than 2% organic carbon (OC). Low soil OC storage is linked with negative environmental impacts including soil and water quality, climate change and biodiversity. A relevant strategy to enhance soil OC is the transformation of waste products into organic amendments for application on soils. The aim of the H2020 European project Circular Agronomics is to provide a comprehensive synthesis of practical solutions to improve the current C, N and P cycling in European agro-ecosystems. This project explores the medium and long-term effects of new and classical organic fertilizers in six countries including Germany, Spain, Italy, Netherlands, Czech Republic and Austria. The study sites will be sampled before and after applying the new organic amendments using a hydraulic corer. A full profile assessment of the C, N and P distribution, stability and bioavailability will be released up to one meter depth using a combination of classical bulk chemical analyses and state-of-the-art imaging techniques. Undisturbed soil cores will be scanned using a hyperspectral camera to reveal hotspots of C, N and P storage in the soil profile, at the micro-scale. Soil C, N and P will be modelled as a function of spectral response using a variety of machine learning approaches. These results will provide essential information to develop management strategies that reduce nutrient surplus and increase C stocks.

Studies on soil organic carbon (SOC) stocks mostly focus on topsoils (< 30 cm). However, 30 to 63% of the SOC are stored in the subsoils (30 to 100 cm), and the factors controlling SOC storage in subsoils may be substantially different than in topsoils. The low mean SOC content in subsoils makes its quantification and characterization challenging. Thus, new approaches are required to depict the SOC stocks distribution in full soil profile. Hyperspectral imaging of soil core samples can provide high spatial resolution of the vertical distribution of SOC in a soil profile. The main objective of the ongoing study, within the Horizon 2020 European Project Circular Agronomics, is to apply laboratory hyperspectral imaging with a variety of machine learning approaches for the mapping of OC distribution in undisturbed soil cores. Soil cores were collected down to a depth of one meter in grasslands of 15 organic farms located in the Lungau Valley, in Austria. Some samples were divided into five depths in the field for classical bulk soil measurements (total carbon and nitrogen, texture, pH, EC and bulk density) on disturbed samples. Undisturbed soil cores were sliced vertically for laboratory hyperspectral imaging in the range of Vis-NIR (400-1000 nm). We were able to reveal the hotspots of OC and map the OC distribution in soil profile by applying a variety of machine learning approaches (i.e. partial least square and random forest regression) as a function of spectral responses. A digital elevation model was further exploited to investigate the effects of topographical factors such as elevation, aspect and slope on SOC profile distribution. Landsat 8 data were also used to depict the spatial variability of land insensitive cover/vegetation in study area.

It is estimated that only 20% of fertilizers applied annually in the European agricultural systems are converted to finished products for human consumption. These low efficiencies result in large loss of nutrients into the environment with severe negative influences on soils, water and air, and constitute unacceptable health and environmental costs. In addition, around 45% of soils in the European countries have less than 2% organic carbon (OC). Low soil OC storage is linked with negative environmental impacts including soil and water quality, climate change and biodiversity. A relevant strategy to enhance soil OC is the transformation of waste products into organic amendments for application on soils. The aim of the H2020 European project Circular Agronomics is to provide a comprehensive synthesis of practical solutions to improve the current C, N and P cycling in European agro-ecosystems. This project explores the medium and long-term effects of new and classical organic fertilizers in six countries including Germany, Spain, Italy, Netherlands, Czech Republic and Austria. The study sites will be sampled before and after applying the new organic amendments using a hydraulic corer. A full profile assessment of the C, N and P distribution, stability and bioavailability will be released up to one meter depth using a combination of classical bulk chemical analyses and state-of-the-art imaging techniques. Undisturbed soil cores will be scanned using a hyperspectral camera to reveal hotspots of C, N and P storage in the soil profile, at the micro-scale. Soil C, N and P will be modelled as a function of spectral response using a variety of machine learning approaches. These results will provide essential information to develop management strategies that reduce nutrient surplus and increase C stocks.

Poster presentation at at the 7th International Symposium on Soil Organic Matter (SOM2019), in Adelaide, South Australia, from the 6th to the 11th of October.

Sustainable agricultural practices aim to ensure the rebuilt of soil organic carbon (SOC) stocks and to sustain soil fertility. One of the levers is the use of carbon and nutrient inputs in the form of organic amendments, such as farmyard manure, slurry and biogas digestate. These organic fertilizers represent a promising alternative to the mineral fertilizers, which are mainly made from non-renewable resources. The use mineral fertilizers is indeed associated with an excessive use of natural resources and a loss of biodiversity. The effect of organic amendments compared with traditional mineral fertilizers on SOC stocks and soil fertility are uncertain in the longer-term. We aimed at investigating the effects of mineral and organic fertilizers (i.e., manure, pig slurry and biogas digestate) on topsoil and subsoil biogeochemistry, after eight years of application. For this purpose, we sampled soil cores down to a depth of one meter in a randomized field experiment in Germany, running since 2011. A full-profile assessment of the carbon and nitrogen distribution, stability and bioavailability was achieved using a combination of classical bulk physico-chemical analyses (e.g., SOC and nitrogen contents, texture, pH, bulk density) and state-of-the-art imaging techniques. Selected samples were analysed for aggregate size distribution, as well as organic carbon and nitrogen contents and allocation within these aggregates. Further, undisturbed core-samples were scanned using a hyperspectral camera in the Vis-NIR range to reveal hotspots of carbon storage at the soil profile scale. Soil carbon distribution was predicted as a function of spectral response, using a variety of machine learning approaches. The application of organic fertilizers (whatever their nature) resulted in higher SOC contents in the first 10 cm, as compared to the control and the mineral fertilizer treatments. The SOC stocks were + 21-33 % higher in the soil treated with organic fertilizers as compared to the control treatment. The application of mineral fertilizer or digestate, as compared to the control, resulted in higher relative amount of microaggregates (versus macroaggregates) (+ 19-40 %) in the soil down to 80 cm. These results will provide essential information to develop management strategies that increase nutrient recycling as well as SOC stocks.

The main goals of sustainable agricultural practices are to rebuild soil organic carbon (SOC) stocks and to sustain soil fertility. The use of organic amendments such as manure, slurry and biogas digestate, as sources of carbon and nutrients, is one of the levers to achieve these goals, as an alternative to the use of mineral fertilizers. However, the effects of organic amendments compared with traditional mineral fertilizers on topsoil and subsoil SOC stocks and soil fertility are still uncertain. Hence, we aimed at investigating the effects of mineral and organic fertilizers (i.e., manure, pig slurry and biogas digestate) on topsoil and subsoil biogeochemistry, and soil structure, after seven years of application. To this end, we sampled soil cores down to 1 m depth in a randomized field experiment in North Germany, running since 2011. We quantified the SOC and nitrogen stocks, as well as some nutrient contents (e.g., nitrate, available phosphorus). Selected samples were further analysed for aggregate size distribution, as well as organic carbon and nitrogen contents within these aggregates. A hyperspectral camera in the range of Vis-NIR was used to scan undisturbed core-samples in order to reveal hotspots of carbon storage along the soil profile. Soil carbon distribution was predicted as a function of spectral response coupled with a machine learning ensemble. Overall, the mean SOC stocks were low (53 t ha-1), reflecting the sandy loam texture of the Northeast German soils under permanent cropping. The application of organic fertilizers (whatever their nature) resulted in higher SOC contents in the first 10 cm (+26 %) and from 20-40 cm (+30%), as compared to the mineral fertilizer treatments. The application of mineral fertilizer or digestate, as compared to the control, resulted in higher relative amount of microaggregates (versus macroaggregates) (+ 19-40 %) in the soil down to 80 cm. These results will provide essential information to develop management strategies that could increase nutrient recycling as well as SOC stocks.