Predicting organic carbon in European soils: Only in Southern Ukraine can we expect an increase in humus content

Abstract

Soil organic carbon comprises the majority of the terrestrial soil carbon pool and plays an important role in the global carbon cycle and balance. Even minor changes in soil organic carbon (SOC) can have a significant impact, not only on climate but also on ecosystem stability, due to its key role in soil-atmosphere carbon exchange, plant growth, and food production. In order to assess the feedbacks between the terrestrial carbon cycle and climate change, and to maintain ecosystem functions, it is crucial to understand the spatial and temporal changes in SOC and the drivers of these changes. The role of soil as a source or sink of atmospheric CO2 is primarily influenced by changes in climate and soil water content. Climate change, particularly global warming, can have a direct or indirect impact on the decomposition of organic matter by regulating soil microbes and fauna, enzyme activity, and soil respiration. A warming climate may increase the loss of soil carbon to the atmosphere because warming has a stronger effect on respiration than on photosynthesis, resulting in a positive soil carbon-climate feedback. Climate warming can significantly affect soil organic matter stocks, with the magnitude of the effect largely dependent on the initial organic matter stock size. Soil carbon content is a crucial aspect of terrestrial ecosystems that affects their functional properties and the climate. Conversely, climate also has an impact on soil organic carbon content. The spatial variability of soil organic carbon content and the predictions made for the west-central European region are also important considerations. The study identified the spatial variation of soil organic carbon throughout Europe and forecast its dynamics in the next 50–70 years, considering global climate change. Digital soil mapping enables a more precise representation of soil properties in space, including the spatial quantification of prediction errors. The accuracy of these predictions increases as more local observations, such as soil profiles, are available to construct the prediction model. Digital soil mapping allows flexible spatial development of soil property maps. Soil properties, such as nutrient concentration and stocks, carbon, heavy metals, pH, cation exchange capacity, and physical properties like particle size and bulk density, can be modelled at different depths and spatial resolutions depending on the project's objectives and available input data. The r GSOCmap project used a 1 km grid to model soil organic matter content. In Europe, the range of soil organic carbon content is from 0 to 750 t/ha, with a mean of 78.1 t/ha and a standard deviation of 50.1 t/ha. Climatic factors were found to account for 29% of the variation in soil organic carbon based on regression analysis. The study revealed that an increase in air temperature leads to a decrease in soil organic carbon content, while an increase in precipitation results in an increase in this indicator. Additionally, the content of soil organic matter is negatively impacted by an increase in the seasonality of precipitation. According to the forecast, global climate change will cause an increase of 1.0–1.1 t/ha in the organic carbon content of 3.6% of the continent's area over the next 70 years. On 7.6% of the area, the changes will be insignificant. The soil organic carbon content is expected to decrease on 88.9% of the area. Of this, 35.1% will experience a slight decrease in carbon content by 0–1 t/ha, 28.4% will experience a moderate decrease in soil organic carbon content by 1.0–1.1 t/ha, and 25.3% will experience a significant decrease by 1.1–1.3 t/ha. The Baltic countries, Belarus, and the Black Earth zone of Russia are at the highest risk. The risk of Russia becoming highly dependent on food imports is increased by this fact. The prospects for Ukraine are quite optimistic. Even in the northern Azov region, we can expect an intensification of humus accumulation processes in the near future, mainly due to increased precipitation. Precipitation in southern Ukraine is a limiting factor that significantly affects agricultural productivity. Increased precipitation and organic matter growth in the soil present positive prospects for agriculture in southern Ukraine, including the northern Azov, Black Sea, and Crimea. It is possible that the occupation of these territories, which are promising for agricultural production, is one of the goals of Russian armed aggression against Ukraine.