14 



CONSERVATION RESEARCH REPORT 5, U.S. DEPT. OF AGRICULTURE 



Table 8. — Weight per head of irrigated grain sorghum as affected by moisture and fertilizer treatments, 



Bushland, Tex., 1959 







Production Data 













Fertilizer treatment 



Head weight at moisture treatment 1 of — 



Average 

 for all 



No. 



N 



p 2 o 5 



Mi 



M 2 



M 3 



M 4 



M 6 



M 8 



moisture 

 levels 



Fj 



Lb. /acre 

 240 

 

 60 

 120 

 240 

 240 



Lb. /acre 

 

 30 

 30 

 30 

 30 

 60 



Lb. 

 0. 104 

 .083 

 .098 

 . 101 

 . 106 

 . 102 



Lb. 

 0. 110 

 .093 

 . 115 

 . 112 

 . Ill 

 .099 



Lb. 

 0. 113 

 .086 

 . 125 

 . 117 

 . 110 

 . 114 



Lb. 

 0. 144 

 .076 

 . 134 

 . 141 

 . 142 

 . 133 



Lb. 

 0. 148 

 .073 

 . 133 

 . 135 

 . 140 

 . 141 



Lb. 

 0. 145 

 .086 

 . 142 

 . 139 

 . 141 

 . 131 



Lb. 

 0. 127 



F 2 



. 082 



F 3 .__ 



. 124 



F< 



. 124 



F 6 



. 125 



F 6 - 



. 120 







Average . 







.099 



. 107 



. Ill 



. 128 



. 128 



. 131 



. 117 















Analysis of Variance 











Component 



Degrees 

 of freedom 



Mean 



square 



2 



Moisture (M) 



5 

 15 



5 



25 



90 



143 







0. 004358** 



Error (a) 



. 000108 



Fertilizer (F) .__ 



. 007082** 



MXF 



. 000416** 



Error (b) 



. 000057 



Total . .__ 









1 See p. 5 for irrigation schedule. 



a **_ Significant at the 1-percent level 



Water Use Efficiency 



Water use efficiency, expressed in units of 

 marketable products per unit of water evaporated 

 and transpired during the growing season, is 

 frequently used to evaluate water management 

 practices. The term indicates the relative effec- 

 tiveness of agronomic and irrigation practices in 

 maximum utilization of water supplies. Water 

 use efficiencies for the 4 years are summarized in 

 table 19 in the appendix. 



Fertilizer Effects 



Fertilizers are extremely important when at- 

 tempting to obtain maximum production per unit 

 of water. The effect of both soil moisture and 

 nitrogen on water use efficiency after 4 years of 

 irrigation is shown by data for 1959 (table 19). 

 With low moisture levels, nitrogen did not increase 

 water use efficiency greatly. When soil moisture 

 was not limiting, nitrogen fertilizer more than 

 doubled the production of grain per unit of water. 

 The large difference in water use efficiency was due 

 to the use of nitrogen, which more than doubled 

 grain yields but increased seasonaTevapotranspira- 

 tion less than 10 percent. 



Annual Variations 



In a dry year such as 1956, water use efficiency 

 with limited irrigations was low, but in the years 

 of normal or above normal well-distributed precipi- 

 tation, relatively high water use efficiency was also 

 obtained with limited irrigation treatments. In 

 contrast, medium to optimum soil moisture and 

 adequate nitrogen fertility resulted in high water 

 use efficiencies in seasons with below normal, 

 normal, and above normal precipitation. 



Irrigation Water Use Efficiency 



Irrigation water use efficiency was evaluated by 

 considering yield increases over nonirrigated crop 

 yields per unit of irrigation water applied prior to 

 planting and during the growing season. The 4- 

 year average production of grain per acre-inch 

 of irrigation water applied is presented in table 9. 

 The highest 4-year average irrigation water use 

 efficiency occurred on the optimum soil moisture 

 level. With the irrigation practices used in this 

 study — that is, a preplanting irrigation plus two or 

 three 4-inch irrigations during the growing sea- 

 son — the largest average production of grain per 

 unit of irrigation water required 14 to 16 acre- 

 inches of irrigation water per acre per year. 



