PARTIAL SOIL STERILISING WITH STEAM AIR MIXTURES - SOME EXPLORATORY EXPERIMENTS

R.A.H. JOHNSON
Heating soil to 180°F has long been recognised as an effective means of partial soil sterilisation. To achieve this the most common method has been to use steam injected into the soil by Hoddesdon pipes, spiked pipes or variants on these. In the last few years the 'strip' method, generally using plastic sheet, has become popular.

However, in all these methods the use of pure steam has inevitably led to the soil being heated locally to the steam temperature to that optimum sterilising conditions are not attained.

To achieve a lower heat-treatment temperature a mixture of steam and air may be used: when this mixture is passed through soil the soil will eventually achieve the same temperature as that of mixture.

This paper describes the apparatus and results of some experiments with steam-air mixtures.

The first elementary apparatus was developed at N.I.A.E. for G.C.R.I. to carry out biological and chemical investigations on small samples of heat-treated soil. The steam-air mixing unit is based on the injector principle and some typical performance characteristics are illustrated. Examples of biological and chemical results are given.

A large-scale experiment in a cucumber house using the same method of steam air mixing is described. The rigid hood method shows promise for use on a practical scale, but is not sufficiently developed yet for commercial use. Injection methods, such as buried or spiked pipes etc., were ineffective because of the low mixture pressure available from the injection type steam-air mixer unit (or from any normal rotary blower or fan). The results of this large-scale experiment are not yet available, but some preliminary measurements taken with the current design of hood and with earlier versions illustrate (a) the effect of a good pressure under the hood and (b) a good soil temperature distribution under the hood.

JOHNSON, R.A.H. (1968). PARTIAL SOIL STERILISING WITH STEAM AIR MIXTURES - SOME EXPLORATORY EXPERIMENTS. Acta Hortic. 6, 190-206
DOI: 10.17660/ActaHortic.1968.6.16
https://doi.org/10.17660/ActaHortic.1968.6.16
6_16
190-206