Soil steam sterilization
Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which causes vital cellular proteins to unfold.
Steaming leads to a better starting position, quicker growth and strengthened resistance against plant disease and pests.
"Steam effectively kills pathogens by heating the soil to levels that cause protein coagulation or enzyme inactivation.
In order to pick the most suitable steaming method, certain factors have to be considered such as soil structure, plant culture and area performance.
The usage of heat resistant, non-decomposing insulation fleece saves up to 50% energy, reduces the steaming time significantly and improves penetration.
The usage of heat resistant and non-decomposing synthetic insulation fleece, 5 mm thick, 500 gr / m2, can reduce steaming time by about 30%.
Despite high capital cost, the fixed installation of drainage systems is reasonable for intensively used areas since steaming depths of up to 80 cm can be achieved.
A central suction pipeline consisting of zinc-coated, fast-coupling pipes are connected in a regular spacing of 1.50 m and the ends of the hoses are pushed into the soil to the desired depth with a special tool.
Negative pressure technique generates appropriate soil temperature at a 60 cm depth and complete control of nematodes, fungi and weeds is achieved.
The negative pressure is created by a fan that sucks the air out of the soil through buried perforated polypropylene pipes.
This system requires a permanent installation of perforated pipes into the soil, at a depth of at least 60 cm to be protected from plough.
In contrast to sheet steaming, cost-intensive working steps such as laying out and weighting the sheets don't occur, however the area steamed per working step is smaller in accordance to the size of the hood.
Outdoors, a hood is positioned either manually or via tractor with a special pre-stressed 4 point suspension arm.
Small and medium-sized hoods up to 12 m2 are lifted manually using a tipping lever or moved electrically with special winches.
Sheets are not suitable, since a high pressure up to 30 mm water column arises underneath the cover.
In comparison to other steaming methods up to 30% energy savings can be achieved and the usage of fuel (e.g. heating oil) accordingly decreases.
Modern soil steam sterilization was first discovered in 1888 (by Frank in Germany) and was first commercially used in the United States (by Rudd) in 1893 (Baker 1962).
Since then, a wide variety of steam machines have been built to disinfest both commercial greenhouse and nursery field soils (Grossman and Liebman 1995).
