i6 
COLORADO EXPERIMENT STATION 
WATER USED BY CROPS. 
Prof. F. H. King concludes from his researches and from those 
of other investigators that an average of three hundred and twenty- 
five pounds of water must pass through the plants, and be evaporated 
by them, for each pound of dry matter which they produce. The 
weight of an inch of rainfall on an acre is one hundred and thirteen 
tons. In a crop of wheat grown on dry land, there is about the same 
weight of dry matter in the straw as in the grain. On this basis, one 
inch of water passing through the plants is sufficient for about five 
bushels of wheat per acre. 
Under fair dry land conditions, at least three-fourths of the 
annual rainfall evaporates from the surface and runs off into the 
streams, with most skillful management this leaves not to exceed one- 
fourth of the rainfall to be absorbed by the plants. An annual rain¬ 
fall of twelve inches, falling at the right time, and carefully conserved, 
would, under most favorable circumstances, furnish three inches of 
water to be actually used by the plant—sufficient to produce fifteen 
bushels of wheat. 
It is evident that the production of fifteen bushels of wheat per 
acre, or the equivalent in other crops, from an annual rainfall of 
twelve inches, hangs on slender chances. Where the ground is hard 
or has been plowed too shallow to absorb water well, the run off is 
large. In some seasons the total rainfall is ample, but does not fall 
during the growing seacon, or it comes in heavy, driving showers, so 
fast and so hard that even mellow, deep soil can not absorb it as 
rapidly as it falls. The earth mulch may be carelessly maintained, and 
then the evaporation from the surface of the soil may amount to much 
more than three-fourths of the rainfall. The seed may be shiftlessly 
put in, the plants so thick in places that a good supply of moisture is 
insufficient and so thin in other places that they can not use all the 
moisture. 
On the other hand, the plowing may be so deep and the soil kept 
in such good tilth that under ordinary conditions much less than one- 
fourth of the rainfall will run off and a greater proportion left in the 
soil available for the plant. 
Four things are necessary to secure profitable crops with the 
limited rainfall of eastern Colorado: 
1. Storage of rainfall. 
2. Retaining moisture in the soil. 
3. Reducing the effects of the wind. 
4. Drought resisting crops from seed grown under dry land con¬ 
ditions. 
STORING RAINEALL. 
Much of the rainfall runs off the surface of the compact, unbroken 
prairie of the Plains. The earliest need is to put the soil in such 
tilth that it will absorb a large part of the rainfall, even when it comes 
