52 THE PRINCIPLES OF AGRICULTURE 



'Sb. Cajjacity is increased by the addition of humus 



73. A study of the above table reveals the 

 fact that the humous soil (33) far exceeds any 

 of the others in its ability to hold moisture. 

 By long- continued cropping and tilling, without 

 making proper returns in the way of green- 

 manures or barn -manures, the humus may be 

 so reduced that the soil consists very largely of 

 mineral matter. One reason why newly cleared 

 lands frequently give more satisfactoiy returns 

 than lands which have been long crojiped, 

 is that the fresh land is rich in humus. The 

 soil is consequently open and porous, and the 

 rain which falls is quickly absorbed, and is 

 largely retained as capillary or hygroscopic 

 water. 



74. The humus of the soil may be gradually 

 increased by plowing under green- crops, by the 

 use of barn-manures, by using cover-crops 

 during the late summer and fall and plowing 

 them under in the spring before they have 

 used up the moisture which should be saved 

 for the succeeding crop. These practices can 

 be overdone, however, and the soil made so 

 loose and open that the winds cause it to 

 dry out quickly, and the power of drawing 

 moisture from the stores of free water will be 

 greatly lessened. 



