Soil structure and water functions in agricultural soils of the temperate-boreal zone in a changing climate

Abstract

Climate change may affect the productivity of cropping systems in the temperateboreal zone by increasing the frequency of periods with water excess and shortage. Soils have the capacity to buffer such extreme weather events by regulating water storage and fluxes, which are mainly a function of soil structure. However, climate itself is linked to the evolution of soil structure through a multitude of processes (e.g., freezing and thawing, soil management). The main objective of this thesis was to improve our understanding of the effects of climate-driven processes on the porespace structure of agricultural soils in order to identify potential implications for soil water functions in the context of climate change. This was done using a wide range of approaches including a meta-analysis, a laboratory experiment, and the application of machine learning to a newly developed index of soil structure based on relative entropy. It was revealed that climate is an important driver of the structural pore space of arable soils in Sweden and Norway. Warmer and wetter regions showed a less developed structure compared to cooler and drier regions, in particular in the subsoil, although it remains unclear whether this was the result of direct or indirect climate-driven processes. With climate change, the number and intensity of freeze-thaw cycles is expected to increase in some parts of the temperateboreal zone. Results from this thesis show that this may lead to increased drainage rates in compacted soil layers under near-saturated conditions as well as improved pore connectivity, especially in fine-textured soils. Furthermore, most changes in pore-space structure induced by freezing and thawing were found for pores of diameters <200 μm. The findings are discussed in the context of wetter soil conditions, early summer droughts, and an intensification of agricultural practices expected for different parts of the temperate-boreal zone in the future.