Soil biophysics – Institute of Soil Science – Leibniz University Hannover

What is soil biophysics?

The soil biophysics working group deals with the interactions of physical and biological processes in soils. It thus combines the classical disciplines of soil physics and soil ecology to form a new overarching discipline that deals with water, material and energy flows in soil ecosystems on different scales and their significance for ecological soil functions

What does soil biophysics study?

Soils are characterised by an extremely complex and spatially heterogeneous architecture. The connectivity of pore networks and the dependent mass transport (water, nutrients, soil gas) as well as the accessibility of interfaces are of central importance for biogeochemical and physical processes. The formation and nature of the soil structure on the micro and macro scale are important properties that contribute decisively to soils being able to fulfil their diverse functions. On the one hand, pore spaces are habitats that can influence biological processes through their physical environment. On the other hand, biological processes (root growth, fauna) continuously reshape the pore spaces so that the soil ecosystem adapts to the boundary conditions and disturbances (e.g. unsuitable soil management or climate change) in the environment as a self-organised structure of interaction mechanisms. We are interested in changes in the soil ecosystem which contribute to impairing soil functions, make soils resilient and help regenerate disturbed soil functions.

How does soil biophysics work?

In addition to classical soil-physical and soil-ecological measurement methods, we use modern methods for structural elucidation (including X-ray tomographic procedures, interface measurements). On the field scale, sensor networks and drone-based thermography are used to record the spatio-temporal variability of soil moisture and surface temperatures. The collected data are used in models to simulate water, heat and solute transport and to quantify the effects of land use on soil ecosystems. Our research projects cover a wide range of scales from individual pore spaces in soil aggregates to the pedon or field scale and cover basic and practice-oriented questions.

Research projects in Soil Biophysics

Influence of soil management

Root-soil interactions

Soil microstructures

Influence of soil management on water, heat and material flows

Land use and urbanisation are considered the main factors for the change of soil properties and thus influence the water, material and energy cycles in ecosystems. On one hand, population growth and climate change lead to an intensification of agricultural and forestry production, e.g. through increased irrigation or mechanisation of production systems, while at the same time weather conditions become more extreme. On the other hand, millions of hectares of fertile soil are lost every day due to soil degradation and land sealing. In this thematic complex, we are investigating how urbanisation in fast-growing metropolises in India (Bangalore) or the intensive driving on forest areas during timber harvesting in Germany affect soil quality and degradation of physical and ecological soil functions. Field and laboratory investigations of soil physical and mechanical parameters in combination with hydrological modelling help to quantify the changes on water, heat and material cycles in different management scenarios. This also includes the question of the extent to which adaptation strategies such as regenerative agriculture through crop rotation design and restorative soil management (compost, gentle soil cultivation) influence the water, material and energy flows between the soil and the atmosphere and whether, among other things, cooling effects can be achieved in the landscape as a result. Drone-based methods such as thermography and in situ sensor networks are used for this purpose.

Root-soil interactions and mechanical processes in root growth

One of our focal points in the field of soil biophysics deals with the interaction between roots and soil. The properties of a soil influence root growth, for example through the grain sizes present, the soil structure and strength, and the content of water and of mineral and organic matter. Root growth, in turn, changes the soil in many ways. Not only are water and nutrients removed, but structural and mechanical properties are also changed. The living root expands in the soil and deforms its environment, leading to the formation of new microstructures and local compression in the rhizosphere. Root exudates modify physical properties of the soil and also represent a carbon and nutrient input into soil. If the root dies, its remains are decomposed, whereby carbon and nutrients become components of new compounds or can be used by other plants, soil organisms and microorganisms. In addition, the resulting pore space forms a new habitat for different organisms and facilitates the growth of other plants whose roots can use the already existing pores.

With the help of laboratory and field experiments, we describe micromechanical and structural properties in the area of the rhizosphere. These include, for example, penetration resistance and measurements of the mechanical deformability of soils and aggregate stability. With X-ray microtomographic images from aggregate to root system level, we describe the 3D pore space structures and evaluate them with quantitative image analysis algorithms. We are interested in the spatial and temporal evolution of the underlying processes and their interrelationships with the newly formed microstructures and how these affect the functionality of the entire root-soil system.

Non-invasive quantification of soil microstructures

Soil structure is a key factor in controlling soil functions. An important component of soil structure are aggregates of different sizes. These have an internal structure, which can be described as a spatial arrangement of solid matter and pore space. Many important biogeochemical and physical processes take place in pore networks and its interfaces to solid matter. Examples are storage and transport of water, nutrients and soil gases, the regulation of the carbon and nitrogen cycles, which are controlled to a large extent by microorganisms and which use a wide variety of pore spaces and niches in soil aggregates as habitats. Another focus of the soil biophysics group is to quantitatively describe the morphological and topological properties of the 3D structure of soil pore spaces from pedon to the aggregate scale and to link them to various soil properties and processes.