28 Nebraska Agricultural Exp. Station, Research Bui. 6. 
fertility, the plant makes a poorer growth, and the water require- 
ment ratio is increased as the condition is extended in the adverse 
direction. This is especially true in relation to grain production. 
Consequently, the amount of soil available for each plant 
should be sufficient to enable it to make a normal growth typical 
of field development. If the object is to determine the need for 
fertilizer applications to a particular soil, care must be exercised 
that the amount of soil rather than its degree of fertility is not the 
limiting factor. It appears that any soil, no matter how fertile, 
will respond favorably to fertilizer application if overcropped. 
In determining the water requirement ratios of different crops 
it is important that the relative number of plants of each crop 
grown in a potometer should bear approximately the same pro- 
portion to one another as are grown under field conditions. Thus, 
in eastern Nebraska we grow in the field 100 wheat plants upon an 
area of land equal to that occupied by one corn plant. Conse- 
quently in comparing wheat and corn in pots we should grow 100 
plants of wheat in a potometer of the same size as we use to grow 
one corn plant. Investigations have shown that plants adjust 
themselves to a certain extent, and the stand may vary somewhat 
without materially affecting results. 
By such an adjustment of the relative number of plants per 
pot, the amount of soil, if it becomes a limiting factor in the growth 
of one crop, does so proportionately with the others as well. In- 
vestigators generally have failed to provide against both over- 
cropping the soil and lack of reasonable uniformity in the degree 
of cropping, in comparing different crops. Thus, Leather (1910, 
1911) grew three to four plants each of 14 different kinds of crops, 
including wheat, barley, oats, linseed, sarson, peas, gram, maize, 
juar, rice, murwa, kodo, rahar, and guar in quantities of soil 
ranging from 14 to 50 kilograms. Pots of uniform size were used 
in each experiment, except where the object of the test was to 
compare the effect of potometers of different size. In Leather's 
experiments a corn plant was given from 3.5 to 12 kilograms of 
soil according to the size of potometer, while wheat, oats, and the 
other plants were given the same amount. His plants were grown 
to maturity. It is very evident from the yields and the photo- 
graphs that the quantity of soil was altogether too small for 
corn and several other crops, while it was much more nearly 
optimum for small grains. Leather also investigated the fertilizer 
requirements of the soil in these small pots and their effect upon 
the water requirements per pound of dry matter. With such a 
relatively limited quantity of soil, neither a satisfactory crop test 
nor fertilizer test could be made. 
Briggs and Shantz have tested 20 kinds of crops, consisting 
