36 BULLETIN 339, U. S. DEPARTMENT OP AGRICULTURE. 



Table XIX. — Percentage of total supply wasted from surface. 



Crop. 



Class of soil. 



Number of 

 irrigations. 



Percentage of waste. 



Maximum. 



Minimum. 



Average. 



Alfalfa 





302 



291 



147 

 122 



Per cent. 

 55.7 

 83.3 

 24.8 

 31.4 



Per cent. 

 0.0 

 0.0 

 0.0 

 0.0 



Per cent. 

 19.1 







25.3 



Alfalfa... 





1.8 







2.3 









Table XIX shows that over one-half of the water applied to grain 

 and alfalfa upon clay loam soils is sometimes wasted, and that the 

 average waste of the total quantity applied was 25.3 per cent for 

 grain and 19.1 per cent for alfalfa. The above figures are based on 

 the results from single fields, however, and irrigators should not be 

 allowed to waste this percentage from their entire holdings. Irri- 

 gated farms should be so laid out that as much as possible of the 

 waste water may be caught up and used over again on one or more 

 fields before it is finally allowed to be wasted from the farm. It Is 

 safe to assume that the average farm could be so laid out that the 

 water would not waste directly off the farm from over one-fourth 

 its area. Rather steep farms, however, of small area, would suffer 

 a larger waste than large farms or those with flatter slopes. Under 

 normal Idaho conditions it is believed that all water contracts should 

 provide for a sufficient delivery over and above the actual water 

 requirements of the soils and crops so that the irrigator could waste 

 between 7.5 and 12.5 per cent of the quantity delivered to him and 

 still retain sufficient for his crop needs. The fact that present 

 economic conditions will not justify a farmer in eliminating all waste 

 must not be overlooked when designing new projects, and the con- 

 tracts should provide for a delivery somewhat in excess of the actual 

 needs of the soil and crops. This is not a serious factor when a 

 project as a whole is considered, for at least one-half of the quantity 

 wasted by the individual farmer can usually be caught up and 

 measured out to other consumers. 



DEEP PERCOLATION WASTE. 



That crops do not and can not utilize at the most more than 2.5 

 acre-feet per annum and that they probably utilize and transpire 

 far less than fchis amount has been proved by the many large yields 

 that have been made in the Idaho investigation with comparatively 

 small supplies of water, and may also be seen from: the curves in 

 figures 3 and 4. Much of the water applied in excess of 2 to 2 J feet 

 per acre in airy region is lost through evaporation, surface waste, or 

 deep percolation. With the more porous soils the loss from deep 

 percolation beyond the reach of the plant roots is the greatest source 



