A RECENT DEVELOPMENT IN STEAM STERILISATION

Later on the more convenient system of sheet steaming was developed, in which steam is blown under a sheet, covering the soil, and left to penetrate the soil. Clay soils can be disinfested very well but on sand and loam soils the results are insufficient.

Nowadays the duration of many cultures has increased, which means that higher standards are demanded of soil disinfestation, so that sheet steaming sometimes, even on clay, proves to be insufficient.

To improve the temperature range in the deeper soil layers, a permanent steam sterilisation system has been developed, in which steam is introduced in drain pipes buried at a depth of about 60 cm, after which the steam moves to the soil surface. The method was an improvement over sheet steaming, especially on sand and loam soils. The most recent development in steam sterilisation is a combination of sheet steaming and steaming via drain pipes; the so-called negative pressure steaming. With this method steam is introduced under the steaming sheet and pulled into the soil by a negative pressure, created in the soil by a fan, which sucks air out of the soil through buried perforated polypropene pipes. The temperatures achieved with negative pressure steaming, are considerably better than those obtained with sheet steaming. In comparison with steaming via drain pipes, negative pressure steaming gives a better result in the upper soil layers, and is almost equal deeper down. This new system is not nearly as expensive as steaming via drain pipes. Moreover fuel consumption can be restricted, compared with the traditional methods.

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