146 CAMPBELL'S SOIL CULTURE MANUAL 



not to let any crust form under the mulch. We are of the 

 opinion that many corn crops have been seriously injured 

 by that condition, when with no more available moisture 

 the crop would have come out all right had it not been 

 for this crust. 



KEEPING MULCH IN CONDITION. 



There are many important reasons why great care 

 should be taken to keep the mulch in perfect condition 

 and prevent the loss as far as possible of any moisture by 

 evaporation from the surface of the soil. The following 

 paragraph taken from Professor King's book on "The 

 Soil," conveys some important information along this 

 line. We quote this because it bears the figures of his 

 own practical observation at various depths in the soil, 

 showing the effect not only of the surface soil getting too 

 dry, but of light showers. He says: 



"When the surface soil has its water contents reduced 

 so the upper six to twelve inches are beginning to get 

 dry the rate of capillary rise of water through it is decreased 

 and it begins to assume the properties of a mulch. But 

 when this condition has been reached if a rain increased 

 the thickness of the water film on the soil grains without 

 causing percolation, the capillary flow may be so certain 

 that the surface foot draws upon the deeper soil moisture 

 at a more rapid rate than before, causing a translocation 

 of the lower soil moisture, the deeper soil becoming meas- 

 urably drier soon after such a rain than it was before, 

 while the surface foot is found to contain more water 

 than has fallen upon it." 



He cites experiments as proof of this important prin- 

 ciple. Some of his experiments were very interesting and 



