WP3: Soil degradation
The main objectives of WP3 were:
1)To develop tools for assessment of desertification/degradation in order to assist managers in their efforts to mitigate its impact on biodicersity and ecosystem services,
2)To monitor changes in restoration sites, and
3) To model scenatios of soil development and degradation based on collected data
The work on this WP was mainly done by University of Bobo-Dioulasso, University of Niamey, and Aarhus University, and the field work was carried out on a south-north rainfall gradient in Burkian Faso and westrern Niger.
To address the first objective a sampling program where soil physico-chemical measurements were related degradation levels measured as both land use/vegetation types and Universal Soil Loss Equation values. The results showed that low values of the commonly known fertility indicators carbon, nitrogen, silt, clay, CEC, and available potassium, can be used as indicators of degradation, while haigh values generally are found in undegraded areas. Furthermore, the results of the sampling program supported the idea of using the quotient “SOC/(silt+clay)” as a degradation indicator. The reasoning behind this indicator is that the silt+clay content defindes the possible fertility of a soil, and the soil organic carbon content (SOC) defines to which extend this possible fertility has been achieved. The suggested indicators of degradation seem to be usefull for managers and they only require standard analyses of soil samples that can be made at laboratories in West Africa.
To addres the second objective annually measured soil physico-chemical parameters from restoration sites were analysed in relation to the tree species planted and restoration techniques. The results show that an improvement of the soil parameters was obtained for restoration techniques carried out in both the semi-arid zone of the Sahel and the more humid Sudanian zone. Thus, in the Sahel area restoration by planting of Guiera senegalensis and Acaci seyal significantly increased soil chemical fertility parameters such as carbon, nitrogen and pH in three years, and in the Sudanian zone stone benches + Piliostigma thonningii planting improved the soil fertility significantly.
To address the third objective collaboration with the EU-fiananced project SoilTrEC was established. In SoilTrEC the Technical University of Crete (TUC) had developed a simulation program CAST, that is capable of simulation the development in soil carbon and water stable aggregates, which are very important for the soil fertility, depending on weather and organic input. The soil physico-chemical measurements from the restoration sites were supplemented with analyses of the content of water stable aggregates and the carbon content of these aggregates. The analyses were carried out according to guidelines elaborated by SoilTrEC, and the data treatment was carried out in close collaboration with TUC. Finally, the simulations with the CAST model using the data from the restoration sites in Niger and Burkina Faso were made in collaboration between SoilTrEC and Undesert at TUC. The simulation results show that stone benches with planting of P. thonningii can relatively quickly reduce the degradation level measured in terms of the SOC/(silt+clay) degradation parameter. Furthermore, the CAST model showed that returning the straw from millet as a mulch layer instead of removing it can also reduce the degradation level in fields, and finally simulations showed that an annual input of 1.2 t/ha was necessary to avoid further degradation at the experimental site in Burkina Faso.
Undesertworks to create an improved understanding of the effects of desertification and degradation processes in West Africa and to develop and implement best practices, such as carbon forestry, in close collaboration between scientists and local communities.
Financed by EU-FP7.