TP3-2: Rhizosphere water

Soil hydrology and rhizosphere processes in agroforestry systems


Water scarcity is one of the major limits to crop production and crop security worldwide. To optimize the availability of soil water for crop roots is therefore a central objective for an efficient and sustainable agriculture. One of the traits that help crops to tolerate periods of water scarcity is to develop deep roots that are able to exploit the water stored in the subsoil. An alternative way to benefit from the water in the subsoil results from the redistribution of water between deep-rooted and shallow-rooted plants, a process called hydraulic redistribution. Hydraulic redistribution (HR) is the transport of water from wet soil layers to dry soil layers through the root system. HR is a passive mechanism driven by gradients in water potentials and it typically takes place when transpiration is low – i.e. during night. The transport of water from the subsoil to the upper soil layers via deep-rooted plants is called “Hydraulic lift” (HL). HL acts as a biological subsurface sprinkler and provides additional water to the roots exposed to soil drying. Additionally, HL has positive effects on nutrient uptake and rhizosphere biology. Agroforestry offers unique and diverse possibilities to optimize water resources available for plants. Trees reduce the exposure to wind and the transpiration demand of crops, resulting in slower water losses which can be beneficial during summer drought spells. Deep roots of trees can bring additional water to the top soil via HL, providing a safety reservoir of water for shallow-rooted crops. Objective of TP3.2 is to quantitatively understand the aboveground and belowground factors controlling soil water distribution and transpiration rate in trees and crops and then to design optimal tree-line distances. Specifically, our objectives are:

  1. To quantitatively determine the factors affecting the gradients in soil moisture below the crops as a function of distance from the trees. TP3-2 will study: root water uptake by trees and crops and the competition in water uptake between their roots; wind reduction close to the trees; hydraulic redistribution during dry spells.
  2. To measure the occurrence of hydraulic lift from deep-rooted trees to shallow-rooted crops and estimate how far this effect extends from the tree lines.
  3. To optimize the design of tree line distances for varying trees, crops, soil properties and climate conditions.


Figure 1 illustrates the measurement design at the research site Reiffenhausen. Water content and soil water tension are measured along a transect at increasing distances from the trees to investigate the effects of trees on soil moisture dynamics below crops. Additional meteorological and plant physiological parameters are provided by other TP´s and measured in field campaigns and experiments (i.e. leaf water potential, transpiration rates, light intensity, wind, air humidity, temperature, etc.).



Prof. Dr. Andrea Carminati

Georg-August-University of Göttingen, Division of Soil Hydrology
Büsgenweg 2, 37077 Göttingen, Germany

Phone: +49 (0) 551 39 46 29
Fax: +49 (0) 551 39 33310

Dr. Martin Jansen

Georg August University of Göttingen, Soil Science of Temperate and Boreal Ecosystems
Büsgenweg 2, 37077 Göttingen, Germany

Phone: +49 551 39 33695
Fax: +49 551 39 33310