TP8: Modelling

Modelling agroforestry systems


In contrast to more complex functional-structural, often individual plant based agricultural crop or silvicultural stand growth models, no such models exist for agro-forestry systems. Moreover, soil processes in available agro-forest models are described in a very simple way, often assumed to be homogeneous for the total root zone. Different soil horizons and their different soil physical, hydraulic and bio-geochemical properties and differences of soil organic matter pools and their turnover rates are not considered. Hence, to better account for the complex interactions between soil biota, nutrient cycling, water uptake and plant growth, a more mechanistic and more dynamic description of water flow, nutrient transport and resource allocation in soil-plant systems is needed. This is in particular important if mixed crop systems are considered to evaluate their sustainability. The objective of this subproject therefore is to describe the different investigated agro-forestry systems by use of an improved process-based soil-plant system model in an integrative way. It is the aim to explicitly simulate water flow and nitrogen uptake in the tree and crop plants including the dependent carbon allocation and plant residue turnover in the soil and at the soil surface. By simulations and scenario calculations we will test and analyse the central project hypotheses based on the experimental findings. Conditions will be identified under which – in contrast to conventional agricultural systems – the considered agro-forestry systems can increase the net value of ecosystem services by improving soil fertility through higher input of crop residues and enhancing nutrient turnover in the soil-plant systems. Also beneficial effects of agro-forestry systems to adapt agricultural crop systems to climate change will be assessed. Based on plot scale simulations we will develop and parameterize a new agro-forestry model that com-bines tree growth and crop respectively grass growth models assuming three different growing zones:

(i) tree strip zone,
(ii) transition zone between trees and crop/grass and
(iii) crop/grass land zone to simulate the complete field scale agro-forestry system.

It is the aim to combine already existing well established growth models (implemented as Expert-N sub-models) in a way that the three different growth zones are adequately represented, in particular concerning differences in abiotic and biogeochemical drivers. The interaction between the growing zones will be described by functional relationships (e.g. for shading) derived from the individual plant based simulations. The model will be parameterized and tested using experimental data obtained within the SIGNAL project. Scenario studies will be performed to analyse possible impacts of various management options (choice of tree vs. crop area, of tree and crop species, of crop rotations, harvesting intervals, exposition) on soil properties and ecosystem services (increase of biodiversity, C-sequestration, reduction of nitrate leaching, flooding and soil erosion). Overall, we will provide evaluated data sets and model interfaces that can be integrated and applied by the future BonaRes Model Center via the model platform Expert-N.




PD Dr. Eckart Priesack

Helmholtz Center München, Institute of Soil Ecology
Ingolstädter Landstr. 1, Neuherberg, D-85764, Germany

Phone: +49 (0)89 3187 3354
Fax: +49 (0)89 3187 3376