Soils are indispensable for plant growth and herewith for the production of biomass, which  can be used as food supply for humans and animals but also as raw material or energy  source. The optimization of crop yields under strongly varying external conditions  (temperature, precipitation frequency and intensity, etc.) is one of the biggest challenges  with respect to biomass production. Soil fertility is linked to its non-rigid porous structure  allowing for roots to penetrate, to store water while air and oxygen is also available and to retain nutrients to be used by plants and recycled by an enormous diversity of soil biota.  Deficiencies in one or more of these conditions might be compensated by agricultural  measures – e.g. compaction by tillage, missing nutrients by fertilization –  on the long run,  however, sustainable biomass production needs to rely on the natural capacity of soil to  provide these essential features.