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. 
Number Number 
of points | Average of points | Average 
Depth. consid- | yield. | Depth. consid: | sepatGe 
ered. | ered. 
Feet Feet 
1b Oe 5S aes Soe eee ee 4 BHU IS A UGeecmcesoosre Seeeretace sae 13 Sal 
eee et mtn tees Kae Me | 11 4s TOGO Deas Soe an qe seers 10 5.38 
A) SES re ee eee et ae 16 AV 4A0S || AMO sees soe oe sac eoeeee | 5 6. 06 
PAIS) So ea ot i ts cao esa SOS eee 16 41862 Deas ariae crac eer ee 3 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 heen 
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 XIII. 
TABLE XIII.—Effect of fertilizer upon yield and irrigation requirements. 
| | Yield of 
| Number | Water | Yield of | grain per 
No. | Method of treatment. Area. | ofirriga- | applied grain acre-foot 
| tions. | per acre. | per acre. | of water 
applied. 
Acres. Feet. Pounds. | Pounds 
tl Umfontilized - 2s See: 5 eens eee are 0. 094 3 1.05 1,000 95 
I sya OES SNES aE ee ade a . 094 5 1.94 1,144 590 
el oeee Ck eee ie sine Same ey See OSG ets | 094 7 2.99 1, 266 423 
4 | Mer bilizedses: 2 S252 8 sty ee ee A OE ee a ee . 092 3 1. 07 1,467 1,371 
inl eee do oe te SS Bt A Se eg ee . 092 5 2.01 | 1,663 
OSeoas GOs OSes Fate SI RS iy Bn ae ee 092 7 3.05 | 1,826 599 
Results during the same season upon fertile alfalfa-sod ground 30 
miles north of Twin Falls, at the Gooding experiment station, indi- 
arte 
SS 
