Soil

Soil forms an integral part of the environment. All plants depend on it as a reserve of nutrients for a healthy functioning, thus making soil essential for the production of food and other crops, but also for maintaining biodiversity and for the landscape. Major nutrients contained in fertile soil are phosphorous, potassium, nitrogen, calcium, magnesium and sulphur. Dissolved, they are taken up through the roots of plants, incorporated into plant biomass and finally returned to the soil when plants die or shed.

Bioenergy production, both from energy crops and from forest and agricultural residues, can affect the naturally balanced nutrient cycles leading to degradation of soil fertility. Removing nutrients when biomass feedstock is harvested from the field, especially in the case of rapid-growth bioenergy crops and complete removal of agricultural residues, ultimately interrupts the natural process by which decomposing plant matter would replenish soil nutrients and effectively makes the soil less fertile. Adverse affects on the community of micro-organisms responsible for nutrient cycling or chemical and physical changes in the soil causing nutrients to be converted into compounds less usable to plants also contribute to the decreased soil fertility.

The nutrient depletion risk can in many cases be lowered by allowing the free decomposition of the most nutrient-rich parts of the plant (leaves, needles, small branches, etc.) and timing the harvest for the part of the growing cycle when the above-ground living biomass has relatively low nutrient content.

Soil degradation – desertification in progress		Unpacked (Switzerland)...		… and packed compost from a biogas plant (Japan)