Success Factor Soil Loosening
In practice soil loosening is an essential success factor for steaming. This can be tracked back to the following factors:
Soil has to penetrate soil in order to be effective. Steam is transported via small gaps between soil components, called capillary tubes. The more tubes available in the soil, the bigger its pore volume respectively, and the easier and quicker steam can penetrate and reach deeper soil layers.
Penetration is a continuous process. Steam enters soil pores and condensates upon contact on the surface of soil particles, clearing space for further steam to follow.
In addition, steam needs surfaces to condensate and release energy for soil decontamination. Loosened soil with fine granulation down to deeper soil layers provides an optimal area for condensation and thus leads to very good steaming results.
Firm, unloosened soil with low pore volume has few capillary tubes and inhibits steam insertion. Only few areas are available where condensation can take place so no space is available for more steam to penetrate. The advancing steam front is thus blocked. Released thermal energy quickly evaporates via thermal conduction to neighboring deeper soil layers – no comprehensive soil heating takes place.
Insufficient soil loosening basically leads to higher energy consumption and less effectiveness. Prior to steaming, soil has to be properly prepared to create a homogeneous soil structure with the highest possible pore volume.
Spading machines are ideal. Milling should not be used, since resulting micro soil particles increase the risk of siltation after steam insertion and condensation which leads to the blocking of capillary tubes.
Clods of Earth
Research has shown that bigger clods with up to 5 cm diameter in loosened soil do not endanger steaming results. Despite the little surface of the clod on which steam condensates in comparison to its volume, under normal conditions sufficient energy penetrates the clod via thermal conduction to heat up its core to up to 90°C and kill all its phytopathogenic organisms. It is just important that steam can fully surround the clod, which is no problem in sufficiently loosened soil.