HUMAX

The HUMAX research project is investigating various measures for humus formation and improving soil carbon content in combinations in order to identify synergies and highlight application options. A special feature is its application in agri-photovoltaic systems (agrivoltaics) and agroforestry systems (AFS). The project combines innovative humus formation methods such as catch crops and biochar to maximise humus formation and carbon sequestration. The effects of these combinations on soil carbon and agriculture are being analysed in order to develop a modular system that helps farmers select optimal measures for their carbon and humus management. Research at Fraunhofer ISE focuses on the systemic and microclimatic analysis of agrivoltaic systems.

To date, little research has been conducted into the potential effects of dual land use by agrivoltaic systems on soil carbon content. However, microclimatic changes have been observed, leading to a reduction in water consumption and an increase in soil moisture, which has resulted in higher crop yields in hot years (see APV-RESOLA results, FKZ 033L098AN). It is therefore to be expected that partial shading by agrivoltaic systems will have an impact on the microclimate and thus on the soil and, where applicable, microbial activity. In addition to humus formation, the combination with AFS opens up further potential as a carbon sink, as the trees and shrubs store carbon in the above-ground and below-ground biomass and also offer great substitution potential through wood products and the material produced during the management of the woody plants. In addition to the carbon stores in the biomass of the woody structures, it has been shown that humus formation in the woody strips can also be significantly increased through diverse ecosystem functions (Seitz et al. 2017).

The dead organic matter in the topsoil, the humus, consists of almost 60% carbon and is therefore of great importance for solution strategies to curb climate change. The agricultural soils in Germany represent an enormous carbon sink with 2.4 billion tons of carbon (Jacobs et al. 2018). Aside from climate protection, an increased stabilized humus content can also improve soil properties such as water infiltration and storage capacity or trafficability and workability. The optimized carbon cycle and humus build-up make an important contribution to adapting to climate change, especially in terms of increasing the resilience of agriculture to extreme weather events such as heavy rainfall and extended dry periods. Although the humus content is also influenced by the climate and soil properties, e.g. soil type, it is changed to a considerable extent by cultivation. This opens up enormous potential for efficiently counteracting climate change through adapted and optimally managed land use systems. Although many measures for building up humus are already known and well researched (Flessa et al. 2019), these have so far only been considered individually.

Apart from climate protection, an increased stabilised humus content can also improve soil properties such as water infiltration and storage capacity or trafficability and workability. The optimised carbon cycle and humus formation thus make an important contribution to adaptation to climate change, especially in terms of increasing the resilience of agriculture to extreme weather events such as heavy rainfall and prolonged periods of drought. Although many measures for humus formation are already known and well researched (Flessa et al. 2019), these have so far been considered mainly on an individual basis.