In plant cultivation it is very important that the soil has proper ventilation. The necessary oxygen supply for the roots and the discharge of the carbon dioxide gas that is formed there, in case of most cultivated growth, takes place via the soil. Also soil chemical processes depend on the presence of oxygen in the soil. The major part of the transport of O2 and CO2 is executed via the so called ‘gas phase’ of the soil, or via the air filled pores. The gas phase is an essential part of the soil; plant growth and soil are seriously influenced by the extend and composition of the gas phase. The air content of the soil depends on the soil moisture content and the soil structure.