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Soil cracking is a well-known phenomenon, also seen in clay soils in the boreal climatic zone. This study was carried out to quantify soil shrinkage properties in six differently managed clay soils in Finland (Vertic Cambisols, 51% clay). Cylinder samples (100 cm3) were taken in spring from two depths (0–5 and 5–10 cm), then saturated with water and dried as a function of applied suction. The heights of the sample were measured after each drying step and the volume of soil was calculated assuming isotropic shrinkage. The volume loss by shrinkage at a suction of −50 kPa was 1.6–3.8% and the total shrinkage was 5.2–10.5% of the total soil volume, respectively. All shrinkage curves showed structural shrinkage which occurred in the matric potential range from saturation to around −6 kPa. The shrinkage curves were characterized by minor proportional and wide residual shrinkage zones. Eight of twelve sites showed a steeper shrinkage in the proportional shrinkage zone than the theoretical 1:1 line. Large slope values, up to 3.0, reflect the collapse of inter-aggregate pore space due to shrinkage pressure. The results indicate significant particle rearrangement and structural changes, e.g. structural collapse and changes in inter-aggregate pore space due to shrinkage pressure. Continuous water saturation and variable periods of freezing between spring and autumn are mostly responsible for soil weakness against increasing effective stress as soil dries. It is presumed that shrinkage behaviour will change substantially with increases in drying and wetting cycles. [ABSTRACT FROM AUTHOR]

Sequestering carbon into agricultural soils is considered as a means of mitigating climate change. We used agronomic soil test results representing c. 95% of the farmed land area in Finland to estimate the potential of the uppermost 15 cm soil layer of mineral agricultural soils to sequester organic carbon (OC) and to contribute to the mitigation of climate change. The estimation of the maximum capacity of mineral matter to protect OC in stable mineral-associated form was based on the theory that clay and fine-sized (fines = clay + silt) particles have a limited capacity to protect OC. In addition, we used the clay/OC and fines/OC ratios to identify areas with a risk of erosion and reduced productivity, thus indicating priority areas potentially benefitting from the increased soil OC contents. We found that 32-40% of the mineral agricultural soils in Finland have the potential to further accumulate mineral-associated OC (MOC), while in the majority of soils, the current OC stock in the uppermost 15 cm exceeded the capacity of mineral matter to protect OC. The nationwide soil OC sequestration potential of the uppermost 15 cm in mineral agricultural soils ranged between 0.21 and 0.26 Tg, which corresponds to less than 2% of annual greenhouse gas emissions in Finland. The fields with the highest potential for SOC accrual were found in the southern and southwestern parts of the country, including some of the most intensively cultivated high-clay soils. Although the nationwide potential for additional OC sequestration was estimated to be relatively small, the current OC storage in Finnish arable mineral soils (0-15 cm) is large, 128 Tg. Farming practices enabling maximum OC input into the soil play an important role as a tool for mitigating the loss of carbon from high-OC soils in the changing climate. Furthermore, especially in high-clay areas with potential for MOC accrual, efforts to increase soil OC could help improve soil structural stability and therefore reduce erosion and the loss of nutrients to the aquatic environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)