12 Nebraska Agricultural Exp. Station, Research Bui. 6 
SUMMARY. 
1. It is concluded from a general review of methods that the 
one best suited for studying the use of water by crops is to grow 
the plants to that stage of maturity at which they are normally 
harvested in farm practice, under control conditions in pots 
sufficiently large to grow a normal plant according to the fertility 
of the soil. This method, however, is, in general, subject to many 
sources of error, which must be overcome in order that reliable 
data of importance may be secured. Many investigations hereto- 
fore reported have been subject to vital errors. Means for the 
elimination of such errors are discussed. 
2. The object of experiments reported in this bulletin has 
been to determine principles according to which water is used by 
crops. In many agricultural districts, water is frequently a 
seriously limiting factor in crop production. It has been thought 
that some means might be devised thru a correct understanding 
of the principles involved, whereby economy in the use of water 
in farm practice could be increased. In this effort there are two 
chief points of attack, namely, (1) adjusting the external factors 
to the needs of the plant, and (2) selecting plants adapted to the 
conditions. 
3. Corn (Zea mays) has been used altogether in a study of 
the relation of environmental factors to the water requirement. 
In addition, several sorghums and sunflowers have been compared 
with corn, and a number of varieties of corn differing in acclimati- 
zation and plant characters were compared. 
Single plants were grown in galvanized-iron pots filled with 
soil. With the exception of an experiment to determine the 
effect of the amount of soil and one small greenhouse test, all 
pots were 16 by 36 inches in size. The amount of soil contained 
varied slightly, according to soil type, and in different years, 
but their capacity was approximately 250 pounds of moisture- 
free soil. 
The rain was excluded and evaporation from the soil surface 
reduced to an almost negligible amount. The quantity of water 
taken up from the soil and transpired by the plant was determined 
by the loss in weight of the entire pot in which the plant grew. 
Except in experiments to determine the effect of various degrees 
of relative saturation, an optimum supply of water was maintained 
practically constant. Except in a few greenhouse tests, all pots 
were situated in a cornfield with their top level with the sur- 
rounding land, so that the exposure of the plants was quite normal. 
