Plants do not live alone! Together with the soil they are the habitat of a multitude of bacteria and fungi. With some out of these groups plants can form a symbiosis that means living together with advantages for both partners. Within fungi there are the mycorrhizal fungi forming symbioses with plant roots. The most widespread form of the root symbioses, the arbuscular mycorrhiza, we can find in more than 80% of all land plants. Besides protection against root pathogens or stress factors the plants gain from the mycorrhizal fungi help with uptake of nutrients. This is important when the nutrients are available in a bound form, not easily solved in the soil solution as after fertilization with mineral fertilizer. The mycorrhizal fungi can take up nutrients far away from the root and special organs formed in the cells of plant roots, the arbuscles (shown in figure 1), deliver the nutrients to the plant and take out in compensation out sugars and other substances as nourishment. Without a symbiont plants have a problem especially with Phosphorous. When the soil is too acidic or too alkaline or the Phosphorous is in an insoluble chemical form plants need mycorrhizal fungi to have access to these P-sources. When compost or bio-char is applied to plants part of the nutrients within these materials are in a more or less insoluble form, depending on the input materials used in bio-char and compost production. When bio-char is produced from animal bones (bonechar or ABC) it contains very high amounts of Phosphorous which is delivered to soil and plant only slowly. Here the symbionts come into play, they form a so called “P-bridge” from the ABC particles to the plant and help to take up the valuable nutrient faster. Figure 2 shows plant growth with and without the fungi. The advantages of bio-chars and composts on one side and the fungal symbionts on the other side urge to develop methodologies for a combined application of both. Therefor this is one of the aims of REFERTIL.