Tort] BRIGGS & SHANTZ—SOIL MOISTURE 211 
Essentials in determining non-available moisture 
In determining the non-available moisture content of a soil, we 
have found that the following precautions are necessary: 
1. The soil mass should be as uniform as possible, since the non- 
available moisture varies with the texture of the soil, and is con- 
Sequently affected by stratification or other non-uniformity of the 
soil mass. 
2. The soil should be brought to a uniform moisture content 
before being placed in the pots. Otherwise, small volumes of soil 
may remain dry and thus introduce an error in the final moisture 
determinations. 
3- All loss of water from the soil should be prevented except 
that resulting from the transpiration of the plant. Otherwise, 
the surface soil may dry out below the minimum limit of available 
moisture, before the inner soil mass has reached this limit. 
4. All sudden fluctuations in temperature must be avoided. 
Otherwise, condensation will occur on the inner walls of the pot 
as the result of distillation from the soil, due to the difference of 
temperature. This condensed water will be absorbed by the roots 
in contact with the inner walls of the pot, and the moisture content 
of the principal soil mass may thus be reduced below the minimum 
of available soil moisture. 
Description of the method 
Tn working out a practical method embodying the above require- 
ments, which have not been fully complied with in the methods 
heretofore described, we have adopted the following procedure: 
1. The air-dried soil is sifted through a 2 mm. screen to remove 
gravel and to insure greater uniformity. The soil, after sifting, 
ae thoroughly mixed, special care being taken to avoid the separa- 
tion of the fine and coarse particles. Variation in the amount of 
Stavel and coarse sand in the different pots produces irregularities 
in the non-available moisture determinations, due to the fact 
that the coarse particles add to the weight of the soil without 
“pPreciably contributing to its water-holding properties. 
In certain soils, notably those deficient in lime, it is best to add 
“Small amount of calcium carbonate to the soil before planting, to 
sure the growth of the seeds. 
