80 



THE IRRIGATION AGE. 



waste. It should always be stored in soils that are 

 to be cropped the following year. The early spring wat- 

 ers should, likewise, be run on the land and made to 

 do duty in producing crops. As before remarked, soils 

 well stocked with water in the spring usually are able 

 to carry crops through the season without much irri- 

 gation; the irrigation of such fields is valuable chiefly 

 in increasing the yield, and making the plant safe dur- 

 ing the critical heated periods. 



It does not matter so much when the water enters 

 the soil. The chief thing is to get sufficient moisture 

 into it. If the wasted waters of fall and spring were 

 used on the fields, the duty of the irrigation stream 

 would again be materially increased. 



to May 4th the total precipitation was in fact 11.5 

 inches. A little more than 82.6 per cent of the total 

 precipitation was thus shown to have entered the soil, 

 and to be stored there at the beginning of the active 

 growing season. 



Such observations have been made on other soils, 

 with practically identical results. Of course, in every 

 case, where such results have been obtained, the soils 

 were plowed in the fall and carefully harrowed in early 

 spring. Similar soils plowed in the spring seldom 

 gathered more than one-third of the natural precipita- 

 tion. 



The land above described, was planted to wheat 

 in the spring, and varying amounts of water were ap- 



Divertlng the Truckee River Into the Flume, Truckee-Carson Project. 



It is a crime against the interests of the arid West 

 to let either fall or spring water run to waste. 



AN EXPERIMENT ON THE VALUE OF THE NATURAL 

 PRECIPITATION. 



On a typical great basin soil, classed as a medium 

 loam, observations have been made for the purpose of 

 determining how much of the natural precipitation 

 may be retained in the soil. In the fall, about the 

 middle of August, after the wheat harvest, the soil 

 was found to contain 9 per cent of moisture to a depth 

 of eight feet. It is an interesting fact that, on similar 

 soils, it appears that wheat can not reduce the soil 

 moisture below 9 per cent. On May 4th of the follow- 

 ing spring the soil was again examined and found to 

 contain an average of 17 per cent of water to a depth 

 of eight feet. Seventeen per cent of water is nearly 

 equivalent to 20 acre inches of water. Deduct from 

 this depth 10.5 acre inches, the equivalent of the water 

 found in the soil in the fall, and there remain 9.5 

 inches, which must have been added to the soil as rain 

 and snow. During the period from August 15th 



plied to the different plots into which the field had 

 been divided. The results follow : 



Depth of Irriga- 

 tion Water Ap- 

 plied During 



Season. 

 (Acre Inches.) 



2.5 

 5.0 



7.5 

 10.0 

 15.0 

 54.0 



Depth of Irrigation 

 Water Applied, plus 

 the Moisture Stored 

 During the Fall and 



Winter. 

 (Acre Inches.) 



12.0 

 14.5 

 17.0 

 19.5 

 24.5 

 63.5 



Yield of Bushels 

 of Wheat 

 per Acre. 



35 



38 

 39 

 42 

 47 

 43 



Even a glance at this table shows that the water 

 stored in the spring must have been active in produc- 

 ing the crop. The first 2.5 inches applied produced 

 thirty-five bushels, while the next five inches produced 

 only four bushels more. If the irrigation is considered 

 as alone having value in crop production, the above 

 table would give the first 2.5 inches a value of four- 

 teen bushels per inch, while the following five inches 

 would have an inch value of only .8 bushel. Such a 



