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STEAM STERILIZATION 
Soil Siribsakor nat Sea 
Today we are more than ever interested in economical operations. Sterilizing soil is definitely a money 
and labor saving method in preparing soils. There are other methods used to sterilize soil but we feel 
that steam is tha most practical. 
Soil sterilization is a protection against certain soil borne diseases, such as Verticillium wilt (Seidewitz 
disease) and root nematodes. Sterilizing by steam changes the physical properties by making the soil 
granular. 
If the soil is high in nitrate, we suggest you apply two inches of alfalfa or red clover hay into the soil 
in place of manure, before sterilizing. Old greenhouse soils used for many years are usually high in 
nitrate nitrogen and are benefited by leaching, after the soil is steamed. 
USEFUL HINTS 
I—Apply manure or red clover hay before sterilizing. Till the soil thoroughly, so that 
the steam may be uniformly distributed. 
2—Have the soil moderately moist, slightly drier than a good potting soil. 
3—Use three inch tile, down spouting or pipe; two lines in a three and one-half 
foot bench. Ridge the soil to the center of the bench directly over the lines, 
covering with tarpaulin, canvas or builders’ felt. 
4—High pressure steam is not necessary. Figure that you can sterilize approximately 
one square yard of soil per boiler horse power. 
5—Do not try to sterilize more than 50 feet of bench in one direction. The longer 
the distance, the longer time required to heat the desired temperature. 
6—Suitable thermometers should be available for determining temperatures at 
various depths. 
7—Cover the sides of the benches so that the entire bench and contents are heated 
to 180°F, 
8—No air should enter the pipe or tile with the steam as cold air causes condensa- 
tion of the steam. 
9—Remove the covering one hour after the steam has been cut. This allows the 
excess moisture to pass from the soil as vapor. 
10—Steam sterilization granulates the soil particles, making for a more porous soil, 
allowing air and moisture to pass through freely. 
11—Steam sterilization usually will increase the soluble salts, nitrate nitrogen and 
ammonia nitrogen over a period of several weeks, although this is not always 
the case. 
12—Leach heavily immediately after sterilizing to reduce excess fertility 
13—Be very careful so as not to contaminate sterilized soils by placing tools, flats, etc., 
on sterilized soil. 
14—The cost of steam sterilization will average 1-!/2 cents per square foot of bench 
area, as compared with 5 cents per square foot when soil is changed. 
We will at all times endeavor to serve you to the very best of our ability. If you have any questions, 
cultural problems, etc., from time to time, please feel free to call upon us. If we are able to help 
you we shall be more than repaid. 
