SIGNAL

Trees have a long tradition in European agricultural systems, but have increasingly disappeared due to modern agriculture. The integration of trees into agriculture in so-called agroforestry systems leads to interactions with crops that, if well managed, allow trees and crops to coexist, be productive and imitate some natural processes that do not occur in monocultures.

The aim of the BonaRes project SIGNAL is to evaluate the advantages and disadvantages of agroforestry systems compared to monocultures. Agroforestry systems are very diverse; SIGNAL has studied rather simple alley cropping systems consisting of poplar rows grown as short rotation plantations in combination with a conventional crop rotation. The scientists compared these agroforestry systems with the same crop rotation without trees and evaluated the following ecosystem functions: Yield, carbon sequestration and greenhouse gas mitigation, soil nutrient cycling and water regulation, biodiversity and erosion control.

The integration of rows of poplars has several agronomic and ecological advantages. Although the presence of trees reduces yields in the first plant rows adjacent to the tree row, this is often compensated for by higher yields in the middle of the plant rows, so that there is no difference in crop yields compared to monoculture.

Agroforestry is more effective at fixing carbon dioxide in biomass, roots and humus. In addition, ecological processes are stimulated in the soil of the tree rows that absorb other greenhouse gases such as nitrous oxide and methane. The carbon footprint of agroforestry is therefore much better than that of monoculture. Despite the positive effect of the trees on the nutrient cycle, the availability of nutrients in monocultures does not differ significantly due to the intensive application of fertilizer. This also has a strong effect on nutrient leaching, which is also comparable. These results indicate that there is potential for lower fertilizer rates without major yield reductions.

In agroforestry systems, biodiversity improves considerably compared to monoculture systems. Within a few years, the tree rows are teeming with earthworms, including deep burrowing species that can significantly improve the water absorption of the soil and are not found in pure cultures. Spiders and the soil microbiome also increase biodiversity and can contribute to pest control. Phytopathological studies show a reduced risk of common plant diseases compared to monocultures. The risk of wind erosion is also greatly reduced in agroforestry systems compared to pure cultures. The high water infiltration rates in the tree rows as a result of the deep burrowing earthworms suggest that the risk of water erosion was also reduced.

The results of the project show that the integration of trees into agriculture plays a very important role in improving the sustainability of agriculture. So why, given these obvious benefits, is agroforestry not currently being used more widely? Our economic analyses show that it currently depends on the location whether agroforestry can compete with agriculture without trees. On some sites it is already economically viable, on others pure crops still have slight advantages. The costs associated with the establishment of agroforestry systems are often an important reason that prevents farmers from establishing agroforestry systems. Providing better financial support for farmers to establish agroforestry systems would make a significant difference.

The project has shown many positive effects of the reintroduction of agroforestry systems, and there is still further potential for improvement, not only in optimizing the systems studied, but also in agroforestry systems with other combinations of trees and crops. Further optimizing management and site- and system-specific adaptations are necessary and can only be achieved by pioneer farmers who are shaping the future of agriculture in a more sustainable way by introducing new forms of agroforestry.

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