A large floriculture enterprise near Pretoria, the capital of South Africa, has completed its changeover to hot steam as a soil sanitising medium in greenhouses. Previously they used 40-50 gram hazardous plant protection chemical per square metre – with good results.

However, the prohibition of methyl-bromide by the Montreal Protocol and the requirement to put it into effect in developing countries by 2015 at the latest necessitated to re-think this conventional method.

Mr Marten Barel, a worldwide active specialist in horticulture, found an alternative method in which hot steam is used.

The system including steam boiler was supplied by MSD Corp. (Durbach, Germany) on the basis of the concept developed by Mr Marten Barel.

In the system, a sandwich-type steaming technology is used. The steam is immediately injected into the soil to 20cm depth via hollow pins of a spiked hood made of load-resistant aluminium. Then an average temperature of 80°C is achieved in 6 minutes. This means a complete sanitisation. After the steaming, the soil is free from weeds, weed seeds and soil-borne pests and pathogens across all the 20 cm depth.

Spiked hood with mechanisms for easy lifting-up, lowering and moving
Spiked hood with mechanisms for easy lifting-up, lowering and moving

The steaming process takes place only under glass. The special steaming hood is operated manually, i.e. moved every 6 minutes (due to low labour cost, the company did not want to purchase a semi-automatic solution with hydraulic components). The steamed surface is promptly covered with a sheet to keep the heat in the soil. In this system, the performance is 600 sq. m a day. The energy consumption is about 0.65 l heating oil per square metre. The result is very favourable for the company since especially very sensitive plants, e.g. Lisianthus, positively react on soil steaming.


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