No. 6. DEPARTMENT OF AGRICULTURE. 169 



neighbors, to be in turn robbed by the neighbor next below. In 

 this way surface tension aids gravity in removing the water from 

 the surface into the soil, and much more rapidly than where the 

 soil in the same mechanical condition is free from moisture. It 

 is the difference between the rate at which the first rain drop trickles 

 down the dry glass, and the next one that follows in the moistened 

 track. For this reason a moist soil gets much more of a shower 

 that gives less than an inch of rain than does a dry soil, because 

 it moves a much higher precentage of it away from the influence 

 of the sun and wind. 



HOW THE WATER IS LOST. 



This will also explain how the water is so easily lost from the soil 

 by evaporation. When the surplus rainwater is removed and drain- 

 age has ceased, then the operation is reversed. The sun, wind and 

 dry air promptly attack the water films on the surface soil grains, 

 reducing their thickness. The surface films give to the air, and take 

 from the films below to make good the loss. In a short time there 

 is a continuous stream from a depth of possibly two feet to the 

 surface to make good the continual loss at that i)oiut. This upward 

 movement is most rapid when the films are thickest and most 

 elastic, and grows less as the films grow thinner, and are held with 

 greater force against the soil surface. The manner in which this 

 loss occurs suggests the remedy or preventive. Change the moisture 

 line from the surface of the ground to a point two inches or more 

 below the surface. Do this by stirring the top soil so as to loosen 

 and dry it out. This enlarges the capillary spaces and breaks the 

 films. Water cannot rise from a half-saturated soil into a dry soil. 

 Two and tv>o and a half inches of dry soil is a very effective mulch, 

 as good as dry straw, but needs renewing after every shower. Keep 

 the surface poll .'ry. This is the lid to tlie soil cistern, ar.d the stop- 

 per to the soil water bottle. 



LOSSES BY EVArORATJON. 



During June. July and August, the greatest loss of water from 

 the soil is by evaporation during the first four days after the rain 

 has ceased falling. The run-olT water and that carried off by sub- 

 surface drainage may seem larger to us, because we can see it, but 

 it is insignificant as compared with the amount of water absorbed 

 by the air. After the fourth dry day the surface of the unshaded 

 soil will have crusted or dried out sufliciently to greatly reduce 

 the upward flow of water, and the interlacing roots will intercept 

 what is left. It is immediately after the shower ceases that the 

 heaviest loss occurs, and it is the promptness with which we stir the 

 exposed soil after heavy showers, or the amount of humus in the 

 soil to enable it to dry out on the surface without crusting or baking, 

 that dotermines how much of the rainfall we lose, or how much we 

 save foj' use by the growing crops. 



TILLAGE. 



We plow, harrow, roll and cultivate that we may separate the 

 particles that have been compacted by the frequent rains during the 



