CHAPTER XIX 



CONTROL OF MOISTURE 



II. TILLAGE 



ONE of the means for controlling moisture that is quite uni- 

 versally practiced is that of tillage. It finds application in arid and 

 semi-arid sections at all times and in humid and superhumid 

 regions, more particularly in periods of drouth. Any form of 

 implement that stirs the soil, from the crudest form of hoe to 

 the powerful tractor with its dozen plows and its harrows, will 

 accomplish the same ohject. 



Increasing the Moisture Capacity of Soils. Probably one of 

 the most important factors in supplying soils with sufficient moist- 

 ure for crops is by increasing their water holding capacity. This 

 may be accomplished by several methods: 



(a) By Tillage. 'Soils frequently become so compact that they 

 will not absorb water readily, hence there will be a large run-off 

 and a consequent loss not only of water but of soil material due 

 to erosion. Only the water that is absorbed can be of any benefit 



i to crops. Hence it becomes very necessary to put the soil in 

 condition to absorb as much water as possible. This can best be 

 accomplished by stirring the soil to considerable depth with some 

 form of plow. The best implement for this purpose is the com- 

 mon mold board plow. In plowing, the soil is not only inverted, 

 but pulverized, and this is very beneficial if the soil is in proper 

 condition with respect to moisture. To increase the storage capacity 

 to the greatest extent plowing should be as deep as possible. The 

 storage capacity may easily be doubled by this means and the soil 

 put in condition to absorb water readily so that very little runs off. 

 This practice is especially advisable on rolling land and in semi- 

 arid regions. 



(b) Compacting the Soil. In the process of plowing the soil 

 is left too loose for retaining moisture to the highest degree, either 

 against percolation or evaporation, 'and in order to bring about 

 proper conditions a certain amount of compacting is necessary. 

 This may be done by various implements, such as the spike-tooth 

 harrow, the disk harrow, the rotary harrow, the corrugated roller, 



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