Transpiration as a Factor in Crop Production. 55 
and water requirements of corn were studied in potometers of six 
sizes containing respectively 32.5, 85, 150, 239, 583, and 956 
pounds of moisture-free soil. The soil was a fertile loam from 
the surface six inches of a productive cultivated field, and was 
uniform thruout all the potometers. The subirrigation type of 
potometer was used, and all growing conditions were uniform 
except the size of potometer and quantity of soil. The shorter 
potometers were elevated so that the top of all were on a level 
with the surrounding cornfield. A single stalk of Hogue's Yellow 
Dent corn was grown to maturity in the center of each potometer. 
All of the seed was secured from the middle of a single ear. A 
duplicate series was grown with all conditions identical with the 
first series, except that well-rotted sheep manure was mixed 
with the upper foot of soil in each potometer at the rate of 4 
pounds per plant as it came from the pile, or 1.75 pounds of 
moisture-free manure. This rate per plant under average eastern 
Nebraska field conditions would amount to about 21 tons of 
moist manure, or 9 tons of moisture-free manure per acre, count- 
ing 10,668 plants per acre. Each size of potometer and method 
of treatment was replicated four times. Figure 10 illustrates the 
different sizes of potometers used. 
Figure 11 shows the relative plant development in the potom- 
eters of different sizes, both without and with manure. A repre- 
sentative plant was chosen from each set. Figure 12 shows the 
actual ears harvested. Four plants were harvested in all but two 
S3ts. One plant in each set of the 16 by 36 inch and 30 by 36 inch 
potometers without manure was broken early by the wind, 
reducing the number to three plants. Several plants produced 
more than one ear. 
The results of the experiments dealing with the size of potom- 
eters are given in Tables 4, 5, 6, and 7, and Charts 1 to 7. 
A detailed study of the tables shows a very marked relation- 
ship between the amount of soil available to the plant and the 
growth and water requirements. An increase in the amount 
of soil rather consistently increased the ear weight, the total 
dry weight of the plant, and the total amount of water transpired. 
It decreased the amount of water used per unit of dry weight 
of plant, altho this decrease was not proportional to the increase 
in weight of plant nor to the increase in the amount of soil. 
The addition of equal quantities of manure to the different 
sized potometers increased the average ear weight 722.5 per cent 
in the smallest and only 2.9 per cent in the largest potometers. 
The total dry weight per plant was increased 176.4 per cent in 
the smallest and only 7.2 per cent in the largest potometers. 
The total amount of water transpired per plant was increased 
