Temperature, holding time and pipe layout determine the result.
Heat coagulates proteins and inactivates enzymes in pathogens, pests and weed seeds. Most soil-borne pathogens die at 50–60 °C within 30 minutes, so 60–80 °C for 30 minutes is sufficient.
Source: Tainan District Agricultural Research and Extension Station, Technical Bulletin 88-3 (No. 89), Steam Disinfection for Plant Disease Control.
| Lethal temperature (30 min) | Organisms killed |
|---|---|
| 100 °C (212 °F) | All plant pathogens and weeds |
| 93 °C (199 °F) | Heat-resistant viruses, actinomycetes, weeds |
| 82 °C (180 °F) | Most weeds and viruses; all plant pathogenic bacteria |
| 60–71 °C (140–160 °F) | Most pathogenic fungi and bacteria; insects, mites, earthworms, snails, centipedes |
| 49–60 °C (120–140 °F) | Rhizoctonia solani |
| 49 °C (120 °F) | Nematodes |
| 38–49 °C (100–120 °F) | Water molds |
Source: Tainan District Agricultural Research and Extension Station, Technical Bulletin 88-3 (No. 89), Steam Disinfection for Plant Disease Control.
Pipes are buried about 20 cm deep and covered with a heat-resistant sheet. Greenhouse test: 6.4 × 60 m per batch with an 808,500 kcal/h machine reached 70–80 °C in 1.5–2 hours; keeping the cover on for 4–5 hours evens out the temperature.
Perforated probes every 30–40 cm are pushed into the soil. With an air-lift frame, moving the set takes 5 minutes — over 10 times faster than by hand.
A rake of hollow tines is towed at about 10 cm per minute while releasing steam. Loosen the soil and remove stones and residues first.
Piling or sun-drying leaves pathogens alive. Steam at 60 °C for 30 minutes, then rest for 7 days before use. A stainless cart (180 × 90 × 50 cm) holds above 60 °C for 4 hours.
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