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 clone 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 : — 



