Healthy Host and Its Requirements 65 



you can see the difference in moisture contents 

 by the difference in color, the moist soil being 

 darker than the dry. Then, if you cover the 

 tumbler to prevent evaporation you can leave 

 the dry soil in contact with the moist soil and 

 there will be no appreciable interchange of mois- 

 ture between the moist and the dry layers. This 

 simple experiment demonstrates that if cultiva- 

 tion is also to conserve the soil moisture, we 

 must always strive to form a pulverized dry 

 mulch on top. Capillary action practically ceases 

 when a dry mulch or layer is found on top of the 

 soil." 



From the trucker's point of view, the water re- 

 quirement of crops deserves careful consideration. 

 In intensive gardening the water supplied by natural 

 precipitation of rainfall cannot always be depended 

 upon for crop production, and must be supplemented 

 by irrigation. In fact irrigation is often a funda- 

 mental requirement, if we are to meet in a timely way 

 the demands of the market. Irrigation when prop- 

 erly carried out may mean success, and the opposite 

 total failure. To be what farmers call a "water 

 hog," using too much water, is detrimental to the 

 crops, for they are very sensitive to an excess of it. 

 Widtsoe and Merrill ' have shown that the yields of 

 truck crops directly depend on the proper amount of 

 water supplied. The result of their investigation is 

 shown in Table 9. 



1 Widtsoe, J. A. f and Merrill, L. A., Utah Agr. Expt. Sta. Bui. 117: 

 69-119, 1912. 



51 



