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BULLETIN 133, U. S. DEPARTMENT OF AGRICULTURE. 



Several years ago it was suggested that the soil-moisture conditions 

 in sections where the winter precipitation was light might be very 

 much improved if the soil was saturated with irrigation water after 

 the crop was removed in the fall. It seemed likely that an applica- 

 tion of water at this time would afford an opportunity for establishing 

 satisfactory moisture conditions, not only in the surface soil but in 

 the subsoil to a depth of 8 feet or more during the time elapsing 

 between fall irrigation and the planting of crops the following spring. 

 It was thought that if this were true better crops might be produced 

 in certain irrigated sections of the Great Plains area if fall irrigation 

 were practiced. In order to determine what effect fall irrigation 

 would have on the crops grown, a series of experiments was started 

 at the Scottsbluff Experiment Farm in the fall of 1910. These 

 experiments were continued in 1911, 1912, and 1913, and three years' 

 results are now available for consideration. An account of these 

 experiments and the results secured is given in this bulletin. 



SOIL CONDITIONS. 



The surface soil at the experiment farm is a sandy loam. At depths 

 varying from 3 to 7 feet the loam is underlain by a stratum of Brule 

 clay varying in thickness from 1 inch to 4 inches. This clay is ex- 

 tremely hard when dry, but it is not highly impervious to water. 

 Under the clay the soil to great depths consists of a very fine sand. 

 This sand is hard when dry, but when moist it is soft and friable. 



RAINFALL. 



As previously stated, the rainfall in western Nebraska is compara- 

 tively light during the fall and winter months. This is indicated in 

 detail in Table I, which shows the precipitation in inches from 

 October, 1910, to December, 1913, inclusive: 



Table I. — Precipitation in inches at the Scottsbluff Experiment Farm from October, 

 1910, to December, 1913, inclusive. 



Year. 



Jan. 



Feb. 



Mar. 



Apr. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Total. 



1910. 





















0.31 



1.10 



1.16 



.47 



0.05 

 .08 

 .37 

 .11 



0.28 

 .34 





 .8 





1911. 





0.45 







0.10 

 .60 

 







1.27 

 .60 



2.31 



3.72 



.13 



0.81 

 1.66 

 3.72 



2.13 

 1.61 

 1.71 



1.28 

 2.45 

 1.30 



0.65 



2.77 

 4.33 



2.14 

 2.70 

 1.18 



11.39 



1913. 





18.51 

 13.75 











Table I shows that the total annual precipitation at the Scottsbluff 

 Experiment Farm was 11.39 inches in 1911, 18.51 inches in 1912, and 

 13.75 inches in 1913. The average annual rainfall of the three years 

 was 14.55 inches. The chief feature of the rainfall in connection 

 with the fall-irrigation experiments is the quantity of precipitation 

 which came during the autumn and winter months each year preced- 

 ing the growing seasons of 1911, 1912, and 1913, when the crops used 



