THE SCOPE AND PURPOSE OF THE IRRIGATION INVESTI- 

 GATIONS OF THE OFFICE OF EXPERIMENT STATIONS. 



By Elwood Mead, Irrigation Expert in Charge. 



With relation to rainfall the territory of the United States is 

 divided into three parts — the humid, the subhumid, and the arid. 

 In the humid region the rainfall is ordinarily abundant, but there are 

 occasional seasons when it is insufficient for the raising of crops, 

 and in most seasons there are times when crops are checked in their 

 growth by periods of drought lasting from a few days to a few weeks. 

 The subhumid region includes the territory where dry periods in 

 summer are the rule. The injury to crops in subhumid regions is due 

 to two causes — insufficient moisture and great irregularity in its dis- 

 tribution. The arid region includes the areas where cultivated crops 

 can not be grown by the aid of rainfall alone. 



Geographically, these regions are arranged from east to west, 

 although no exact line can be drawn separating them. The humid 

 region, as generally described, includes all of the United States west- 

 ward to a line which would cross Nebraska and Kansas about halfway 

 between their eastern and western borders. The subhumid region 

 lies between the humid and arid regions, extending from the Gulf of 

 Mexico to Canada and including irregular areas in the different 

 Pacific coast States; while the arid region includes all the territory 

 lying west of the eastern subhumid belt with a considerable exception 

 along the Pacific coast, and with smaller local areas in each of the 

 arid States. 



Irrigation is employed as an aid to agriculture in all of these 

 regions. It is a necessity in the arid region, of great value in the 

 subhumid district, and is proving highly profitable in the growing of 

 certain crops in the humid region. There are also large areas in the 

 recently acquired insular possessions of the United States where irri- 

 gation is required, and where the value of the products permits of a 

 large outlay to provide for its use. The work of the irrigation 

 investigation of the Office of Experiment Stations covers therefore 

 the whole of the United States. 



INVESTIGATIONS IN THE ARID REGION. 



The greater part of the irrigation work of this Office has been car- 

 ried on in the region where farming is impossible without the artificial 

 H. Doc. 334 27 417 



