03 Physics of ilie Soil. 



112. Drainage the Ultimate Remedy. Drainage must be 

 the ultimate remedy for any alkali land, as it can be only 

 a matter of time when any fertile soil will develop enough 

 undesirable soluble salts to render it sterile or less produc- 

 tive, unless the soluble salts not needed are removed, and 

 only drainage can do this. 



113. Deep and Frequent Tillage Helpful. It is clear that 

 whatever means will prevent the excessive evaporation of 

 water from the surface will in so far lessen the concentra- 

 tion of salts there, and hence frequent and deep cultiva- 

 tion, to form effective mulches, will lessen the rise of 

 water, and therefore of salts, to the surface and in this way 

 permit crops to be grown on soils which are critically near 

 the limit of sterility on account of the high salt content. 



114. Change in Soluble Salts with Season. In Figs. 29 

 and 30 are represented the changes in the nitrates and total 

 soluble salts in the surface four feet under three fields of 

 corn, beginning with April and ending with Sept. Re- 

 ferring to the nitrate curves it will be seen that the nitrates 

 start in April nearly equal in the four feet, but increase 

 rapidly in the first foot until the middle of June, when 

 the corn begins to draw on the supply. From this time 

 they decrease rapidly until the middle of July, when they 

 are less than in April and less than in the second foot. By 

 the middle of August, when the crop has ceased to draw 

 much but water from the soil, there is a slow increase again 

 and then one more rapid after the corn is cut, Sept. 1. 



The change in the total salts is much less marked, but 

 evident, there being a general decrease. The mean amount 

 of salts at the beginning and at the end of the season are: 



April 18. Sept. 1. 



Total salts 540 363 



Nitrates 86 82 



Difference 454 331 



From these figures it appears that the salts, other than 

 nitrates, h'ave decreased during the season 123 Ibs. per mil- 

 lion of the dry soil for the four feet, or 1,968 Ibs. 



