LOCAL CONDITIONS WHICH AFFECT DRY FARMING. 17 



thawed out in the spring; while on shallow soils or soils Avith a 

 relatively small amount of tine material, and consequently a low 

 water-holding capacity, the rain that falls, except during the grow- 

 ing season, is largely lost by percolation to depths beyond the reach 

 of plants. 



It is well known that moisture may be lost very rapidly from a 

 soil if the surface is not stirred soon after a rain. It is, therefore, 

 only with intertilled crops that rain can be economically utilized 

 during the hot growing season. For crops that can not be inter- 

 tilled, such as wheat, oats, and barley, the greatest economy of soil 

 moisture is possible if no rain falls after the crop is sown, or at least 

 after the last surface tillage is given." "Where the soil is fairly 

 heavy and deep it can hold available sufficient moisture to mature any 

 ordinary crop, provided losses by direct evaporation are nearly or 

 quite prevented. 



The growing season of the ordinary crop plants is set within fairly 

 definite limits. If moisture is not supplied at about the time it is 

 needed, the i)lants either die outright or are injured beyond recovery. 

 In farming with a limited rainfall there is therefor nmch less risk 

 involved where it is possible to store in the soil during a whole year 

 enough w^ater to carry a crop to maturity than where it is necessary 

 to depend on the chances of rains at just the proper time during the 

 growing season. There is nnich less chance of a year-long drought 

 than of a drought of two or three weeks during the summer when 

 rain is badly needed for crops. 



In figure 3 is shown the average monthly precipitation at four 

 representative points in the eastern part of the Great Basin, while 

 for purposes of comparison similar diagrams are shown of the pre- 

 cipitation at four representative points in the Great Plains area 

 which lies on the eastern slope of the Rocky Mountains. The dia- 

 grams are arranged to show the average amount of jjrecipitation in 

 inches of water for each month in the year, and the months are 

 arranged in the order of the calendar year, with January on the left 

 and December on the right. 



It may be seen at a glance that the seasonal distribution of the 

 precipitation is strikingly different in the tAvo regions represented. 

 In the Great Basin the larger part of the rain falls in the autumn, 

 winter, and early spring, while except at Parowan ^ the midsummer 

 rainfall is almost negligible. On the other hand, the characteristic 



o In the ease of autumn-sown cereals it is not only practicable but decidedly 

 advantageous to barrow the crop in the spring as late as it can be done without 

 injuring the grain. 



& Parowan is evidently far enovigh south to share somewhat in the torrential 

 summer rains that often occur in Arizona and New Mexico. 



103 



