Design and Fabrication of a Heated Air Soil Sterilizer for Greenhouses and its Performance

Abstract

We should like to report the soil sterilization method using the heat in the closed PVC green-house during the summer effectively. The outline of the investigations are as follows.
1. In the apparatus as shown in fig. 1 when circulating the hot air which raised up to 70°C by the solar energy only to the buried pipes in the soil, the soil temperature under 25cm from the surface was 57°C and in the case of no-circulating it was 32°C respectively. So the circulating effects in regard to raise of soil temperature were recognized for deep layer soil remarkably.
2. As for the die out temperature of diseases in the method which the dry heated effects and the wet heated effects for the diseases germ were recognized to coexist together in the die out function, the laboratory and field tests were carried. And the 60°C during 10 minute were obtained for the Fusarium Oxsporum, the Verticillium Albo-atrum and the Plasmdio Phora Bassicae Woronin.
3. When the die out temperature for soil diseases germ was determined as 60°C, it was necessary to supply the insufficiency heat for the soil sterilization. So we have investigated the supplying method of it. The outline of this method were as follows.
1) Four radiating pipes of diameter 10cm which buried with uniform distance to the cross section of the 1.2m wide bed were required.
2) On account of the working method the radiating pipes of 20m in length was convenience.
3) The 120°C initial temperature of heated air which it have to passing through in a pipe and its velocity of 8-9m/s in a pipe were required respectively.
4) Pressure losses at above mentioned conditions in the apparatus was about 28-32mm Aq.
4. We were reported only the results from the last investigation of various fundamental properties. In the following section, we shall report the design and fabication of the air heater, its attachments and results of the practical use.