24 



BULLETIN" 339, U. S. DEPARTMENT OF AGRICULTURE. 



represented by the point where the various lines crossed each 0.5 

 foot in depth were then averaged, thus fixing the curve. 



Table XII. — Averages upon which alfalfa curve is based.- 



Depth. 



Number 

 of points 

 consid- 

 ered. 



Average 

 yield. 



Depth. 



Number 

 of points 

 consid- 

 ered. 



Average 

 yield. 



Feet. 

 1.0 



4 

 11 

 16 



3.57 

 4.10 

 4.40 

 4.86 



Feet. 

 3.0 



13 

 10 

 5 

 3 



5.30 



1.5 



3.5 



5.38 



2.0 



4.0 



4.5 



6.06 



2.5 



16 



6.96 







The curves in figures 3 and 4 show the average yields which were 

 produced on the average clay loam soils of southern Idaho with 

 given volumes of water, there having been a wide divergence in the 

 results upon which they are based, and it should not be inferred that 

 they will check exactly with the results from any individual farm. 



The effect of fertility on the return of grain from the use of given 

 quantities of water is illustrated further by an experiment which was 

 carried on at the Twin Falls experiment station during the season of 

 1914. Six adjoining one-tenth-acre plots of rather infertile soil 

 were planted to Marquis wheat. The land devoted to these plots 

 had been farmed to grain six years after the sagebrush had been 

 removed. Three of the plots were fertilized moderately, with appli- 

 cations at the rate of 15 loads of barnyard manure per acre; the 

 remaining three were left in their original condition and did not 

 receive any fertilizer. Two of the plots, one fertilized and one unfer- 

 tilized, received an application of 1 foot of water per acre; the second 

 two plots, one being unfertilized, received an average application of 

 2 feet per acre; and the third set of two plots, one of which was unfer- 

 tilized, received an application of approximately 3 feet per acre. 

 The results secured are shown in Table XTII. 



Table XIII. — Effect of fertilizer upon yield and irrigation requirements. 





No. 



Method of treatment. 



Area. 



Number 

 of irriga- 

 tions. 



Water 

 applied 

 per acre. 



Yield of 



grain 

 per acre. 



Yield of 

 grain per 

 acre-foot 

 of water 

 applied. 



1 



Unfertilized 



Acres. 

 0.094 

 .094 

 .094 

 .092 

 .092 

 .092 



3 

 5 



7 

 3 

 5 



Feet. 

 1.05 

 1.94 

 2.99 

 U07 

 2.01 

 3.05 



Pounds. 

 1,000 

 1,144 

 1,266 

 1,467 

 1,663 

 1,826 



Pounds. 

 952 



?, 



do 



590 



3 



do 



423 



4 





1,371 



5 



do 



827 



6 



do 



599 









Results during the same season upon fertile alfalfa-sod ground 30 

 miles norlh of Twin Falls, at the Gooding experiment station, indi- 



