ii!i;i<;ation k\im:i;imkxts ix idaiio. 3 



selection of tracts. 



As it was imperative that the final results of the investigation 

 should show a duty that could be secured by good average farmers 

 without more expensive preparation than would be justified, only 

 such tracts as were considered typical in regard to soil and practical 

 in regard to preparation were included, and they were not especially 

 prepared for the investigation in any way. 



DIVISION OF TRACTS AND VARIATION OF WATER. 



Each tract selected, wherever its topography and size permitted, 

 was divided into three approximately equal parts, care being taken 

 to select only such tracts as had uniform soil conditions and previous 

 preparation and cropping throughout, hi order that the results from 

 the different plots might be strictly comparable. In most cases the 

 tracts consisted of about 15 acres, divided into three plots of about 

 5 acres each, in the same crop on the same soil, with all conditions 

 uniform, except that a different volume of water was applied to each 

 plot. 



Weirs were installed in the ditches leading to and from each tract 

 in order to measure the water applied and wasted. These tracts 

 were selected from average irrigators' farms in representative dis- 

 tricts, and the owner of each was allowed to select one of the plots 

 into which his tract had been divided and to irrigate and handle it 

 during the season and apply the water at such times as had been his 

 usual custom. The two remaining plots were irrigated by applying 

 more water to one and less to the other than the owner applied to the 

 plot he himself had selected. The yield produced usually indicated 

 which plot had received the supply of water best suited to the soil 

 and crop in question. Usually four or five experimental tracts were 

 selected from as many farms in the same neighborhood, since one 

 assistant could look after and irrigate that number of tracts pro- 

 vided the same were located within a radius of 2 or 3 miles. The 

 water wasted from each tract was measured, and all amounts tabu- 

 lated in this report unless otherwise specified represent only the 

 quantities retained upon the land. 



MEASUREMENT OF WATER. 



Cipolletti weirs were used in the measurements, the weir boxes 

 usually being built of 1-inch lumber. The weir plates used were 

 16-gage galvanized iron. The head on the weirs was measured each 

 hour or oftener, as was required, with small steel rules graduated to 

 0.01 foot. Measurements of the head were made from the tops of 

 spikes driven vertically into substantial 2 by 4 or 4 by 4 stakes placed 

 in the weir pools upstream from the weirs, at about twice their length. 



