12 DRY-FARMING 
dry-farm sections, soil-moisture is lost only by these 
two methods; for wherever the rainfall is sufficient 
to cause drainage from deep soils, humid conditions 
prevail. 
Water for one pound dry matter 
Many experiments have been conducted to deter- 
mine the amount of water used in the production of 
one pound of dry plant substance. Generally, the 
method of the experiments has been to grow plants 
in large pots containing weighed quantities of soil. 
As needed, weighed amounts of water were added 
to the pots. To determine the loss of water, the 
pots were weighed at regular intervals of three days 
to one week. At harvest time, the weight of dry 
matter was carefully determined for each pot. Since 
the water lost by the pots was also known, the pounds 
of water used for the production of every pound of 
dry matter were readily calculated (Figs. 5, 6). 
The first reliable experiments of the kind were 
undertaken under humid conditions in Germany 
and other European countries. From the mass of 
results, some have been selected and presented in 
the following table. The work was done by the 
famous German investigators, Wollny, Hellriegel, 
and Sorauer, in the early eighties of the last century. 
In every case, the numbers in the table represent 
the number of pounds of water used for the produc- 
tion of one pound of ripened dry substance : — 
