36 The Colorado Experiment Station 
crops are grown with success only under irrigation or under “dry- 
farming” methods. These methods of dry-farming are concerned 
with the conservation in the soil of the natural rainfall, that is the 
prevention of the run-off, which is normally rapid, and of evapo¬ 
ration. The rather pronounced variations in the annual precipi¬ 
tation from year to year make dry-land farming a decided success 
some years, and as decided a failure other years. Grass-steppe is 
a region of summer rainfall (see Fig. 10), and dry falls and win¬ 
ters. Hence the germination and growth of summer annuals is fa¬ 
vored, while winter annuals frequently find the falls and winters 
too dry for their development. Fall-sown wheat is liable to have 
insufficient moisture to bring about germination, and it may suf¬ 
fer from drying out or blowing out during the winter. However, 
in spite of these difficulties, fall-sown wheat usually is a more sat¬ 
isfactory crop on dry land than spring-sown wheat. Spring wheat 
suffers from the late summer period of low rainfall, all the more, 
as this period is accompanied by a high evaporation. A method 
quite in harmony with the seasonal distribution of the rainfall on 
the Great Plains is one in which summer tillage is adopted to con¬ 
serve the rainfall, and is followed by fall-sown grain. This plan 
enables the cereals to survive the dry fall and winter, by calling 
upon the stored soil moisture, and the following season finds them 
well toward maturity before the dry summer months. 
r 
Grass-steppe of the Plains is indicative of temperature con¬ 
ditions favorable to a varied agriculture. Corn, sorghum, millet, 
and the common small cereals are brought to maturity in any por¬ 
tion of its area. The same is true of apples, sour cherries, plums, 
and small fruits, which are grown with the greatest success in the 
Arkansas Valley as far up as Canon City, and adjacent to the foot¬ 
hills from Denver northward. There are, however, local districts 
within these large areas that are not adapted to commercial fruit¬ 
growing. Examination of Figs 2, 5 and 7, shows that these areas 
have an average frostless season of 150 days and over, that the 
average date of the last spring frost is about May 10, and that the 
mean temperature for the summer months is close to 70°. Peaches 
in Colorado are not a safe commercial crop in areas with an aver¬ 
age frostless season of less than 150 days, where the average date 
of the last spring frost is later than May 1 to 10, and where the 
mean temperature for the summer months (June, July and August) 
is less than 65°. However, average length of frostless season, 
average date of last spring frost, and mean temperature for the 
summer months are not sufficient temperature data upon which to 
base a conclusion regarding the desirability of an area for the 
