246 SOIL PHYSICS AND MANAGEMENT 



Moderately deep plowing is very essential, since it prevents loss 

 by surface drainage. 



(b) Fall Plowing. Summer or fall plowing is especially ad- 

 vantageous because it permits the absorption of winter rains and 

 snows, and if cultivation is then done as early as possible in the 

 spring a large amount of moisture may be held in the soil for the 

 use of the crop in the fall or the following season. If the plowing 

 must be done in the spring it should be done as early as possible to 

 catch the rains and hold what is already in the soil. 



The disk can be used to good advantage on either fall or spring 

 plowing to produce deep mulches. Even on stubble the disk can 

 be used to advantage as soon as the grain is removed. If a crop is 

 seeded in the fall, one of the very necessary things is to produce 

 a mulch as early in the spring as possible with some implement 

 adapted to that purpose. 



(c) Summer Tillage and Cultivation. Alternate cropping 

 provides for a crop every other year. To leave the land idle or 

 occupied with weeds would be of no benefit. The object of not 

 cropping during one season is to store moisture for the crop the 

 following year. It is necessary then to put the soil in condition not 

 only to absorb the rain that may fall, but to conserve it afterward. 

 If weeds are allowed to grow the moisture will be lost. To avoid 

 this loss summer tillage or fallowing is practiced. This fits the 

 soil for absorbing water, for conserving it from evaporation by a: 

 mulch and kills weeds that use it. 



Cultivation of crops is as important as summer tillage and 

 should be done to a greater depth than in humid regions. It may 

 be done without injury to the roots of the crops, because the root 

 systems of plants develop deeper in arid than in humid soils. The 

 mulch produced on the surface should not be too fine, but made up 

 of small clods mixed with fine granular material. If a dust mulch 

 is produced, -the first dash of rain causes the soil particles to run 

 together and produces a somewhat impervious stratum which pre- 

 vents rapid absorption and water is lost through surface run-off. 

 Every effort must be made to maintain a mulch until a network 

 of roots is developed and the crop is large enough to shade the 

 ground. Another objection to the dust mulch is that the fine mate- 

 rial is so easily moved by the wind that serious loss of soil may 

 result. 



After a shower falls, the mulch should be renewed as soon as 

 possible. Experiments have shown that of the water lost during 



