Aug. 15,1925 
Soil Disinfection for Potato Wart 
331 
The soil tubes used were practically all 2 by 15 inch glass tubes. 
A few brass tubes were secured, but owing to the corrosive action on 
them of some of the chemicals tested their use was limited. In order 
to have the soil evenly compacted, standard compactors were secured. 
The compactor used for the brass tubes has a propeller in the tube 
and gives the tube quarter-inch drops as it is rotated. The other 
compactor is of the springboard type recommended for use with glass 
tubes. With this compactor the tube rests on the middle of the 
springboard while a weight is dropped from a definite height onto 
the end of the springboard. After a number of tests it was decided 
that six drops of the weight from the top of its guide rod gave a uni¬ 
form compaction with the soils used. Eight-inch sieves of different 
sizes and an electric sieve shaker were secured. This shaker has 
a semirotary and undulatory motion, with a decided jar given the 
sieves when revolved. A series of sieves can be used at the same 
time. 
Soils Used 
The soil used was almost entirely Manor loam from Chevy Chase, 
D. C., or Leonardtown silt loam from Farlee, Va. A few tests were 
run with potting soil from the greenhouses, but this was found to be 
too variable. Manor loam is a common soil type near Washington, 
D. C., containing 20 per cent or more of clay and having a moisture 
equivalent of 20.1 per cent. 9 Leonardtown silt loam, common in 
nearby Virginia and Maryland, contains 15 per cent or less of clay and 
has a moisture equivalent of 23.8 per cent. All Manor loam soil used 
was from a single load of soil, and the Leonardtown silt loam was all 
taken from an area only a few feet in diameter. These soils were 
naturally uniform, and each lot was made even more uniform by 
thorough mixing. The region about Freeland, Pa., is transitional 
between the Volusia and the DeKalb series of soils. Both types are 
silt loams with some tendency to acidity. The coal-miners’ gardens 
in which the wart disease occurs are conglomerations of ashes, 
cinders, coal dust, and soil, so that soil types for the region do not 
necessarily indicate what may actually be found in a given garden. 
Preparation op Soil Tubes 
Soil to be tested in tubes was run through a screen (quarter-inch 
mesh) to remove any roots, stones, and large lumps. The soil for 
each tube was weighed. The amount of soil used in a tube depended 
somewhat on the character of the soil and the tests to be run. In 
some cases 500 grams of the loose soil filled a tube, or the amount of 
penetration to be expected made the use of more soil unnecessary. 
When the soil was in such condition that a larger amount of the loose 
soil would go into a tube and the amount oi penetration expected 
made it advisable, 600 grams per tube was used. In either event the 
soil was compacted as described above. The height of the soil 
columns secured was reasonably uniform. The heights of soil 
columns as given were taken after treatment. The number of tubes 
used in a set varied greatly. The penetration secured was so uniform 
for similar tubes that only three or six of a set of similar tubes were 
ordinarily tested in any one day. This made it possible to run tests 
• Moisture equivalents furnished by John W. McLane of the Biophysical Laboratory, Bureau of Plant 
Industry 
