32 Nebraska Agricultural Exp. Station, Research Bui. 6. 
A deterioration of soil-growing conditions may occur from 
confinement for a period of years in pots, as described in this 
bulletin, pages 157 to 159. 
ENVIRONMENT. 
Experiments have shown that the intensity of the various 
climatic factors bears a close relation to the water requirement. 
Consequently, results obtained under abnormal exposure should 
not be construed to give correct measurements for field conditions. 
To illustrate, Briggs and Shantz (1914) found that 10 per cent 
more water is used by Kubanka wheat fully exposed in an isolated 
place than is used by wheat sunk in a pit level with the ground in 
a wheat field. Again, the fully-exposed wheat transpired relatively 
20 per cent more than wheat in a screened inclosure. Since the 
majority of the crop tests made by Briggs and Shantz (1914, p. 3) 
were made in this screened inclosure, they state that the "in- 
closure measurements, at least in the case of wheat, are less than 
10 per cent below the water requirement of plants exposed under 
field conditions." In this way we are given a basis for correction 
in reducing to field requirements. The authors state (1913 a, 
p. 13) that "the determination of the relative water requirement 
of the different crop plants is, however, the main problem from an 
economic standpoint." It would be of great interest to know just 
how much the various crops differ under field conditions in their 
self-protection against evaporation influences. It seems probable 
that the leaves in a pumpkin field are differently exposed to 
the action of the wind and other climatic influences than are 
the plants in a corn or sorghum field. Again, it appears that the 
dense vegetation in an alfalfa meadow would provide greater 
self-protection against transpiration than the more open vegeta- 
tion of a cornfield. This factor of difference in self-protection 
against evaporation is overlooked when crops are brought to- 
gether out of their normal field conditions and are tested under 
one uniform abnormal exposure. It seems that we must con- 
sider the results in regard to the relative water requirements of 
different kinds of crops obtained in this uniformly exposed 
manner as doubtful until the relative degree of self -protection 
has been determined for each or a similar type of crop. 
THE PLANT. 
Plant individuality may be an important source of error in 
pot tests. The most practical way of overcoming this is by 
replication, which is quite effective as shown in Tables 13 to 21 
of this bulletin. The plants may be replicated either within a 
pot or in different pots. In the former case, care must be taken 
