8 



BULLETIN 1039, U. S. DEPARTMENT OF AGEICULTUEE. 



both 1911 and 1912. The 1913 crop was probably benefited by the 

 abundant late rains in 1912. 



EVAPORATION. 



The seasonal evaporation probably ranks next in importance to 

 seasonal precipitation among the factors which influence the growth 

 of crops at Newell. The daily evaporation has been recorded at the 

 Belle Fourche Experiment Farm, and the total depth in inches by 

 months from April to September is shown in Table II. The record 

 of evaporation was not kept for the month of March, but at Newell 

 crops ordinarily make little growth during that month and hence 

 this omission is not of importance. The evaporation is determined 

 from a free water surface, the method being that employed at all 

 of the stations Avhere the Biophysical Laboratory of the Bureau of 

 Plant Industry has been cooperating.'^ 



Table II. — Monthly evaporation from a free water surface at the Belle Fourche 

 Experiment Fann from April to September of each year, 1908 to 1919, in- 

 clusive. 



[Evaporation and precipitation data in inches.] 





Apr. 



Maj^. 



June. 



July. 



Aug. 



Sept. 



Total. 



Precipitation. 



Year. 



April 

 to Sep- 

 tember, 

 inclu- 

 sive. 



Ratio 



to 

 evapo- 

 ration. 



1908 



5. 535 

 3.657 

 5.408 

 4.649 

 4.849 

 4.705 

 3.369 

 4.454 

 3.689 

 2.018 

 3.278 

 3.519 



5.917 

 6.413 

 5.306 

 8.302 

 6.423 

 4.302 

 5.133 

 3.970 

 5.269 

 4.704 

 5.171 

 6.769 



6.821 



5.859 

 8.975 

 10. 241 

 8.175 

 7.046 

 6.712 

 4.612 

 6.138 

 6.271 

 6.555 

 8.904 



8.081 

 7.698 

 10. 429 

 10. 714 

 7.980 

 8.235 

 8.737 

 5.352 

 7.519 

 9.536 

 6.482 

 9.564 



7.866 

 8.243 

 7. 295 

 6.682 

 6.604 

 8.144 

 6.966 

 5.113 

 5.438 

 6.983 

 7.129 

 8.224 



6.745 

 5.001 

 4.302 

 6.113 

 3.713 

 4.707 

 4.194 

 3.956 

 5.429 

 5.307 

 3.951 

 5.122 



40.965 

 36. 871 

 41.715 

 46.701 

 37. 744 

 37. 139 

 35. Ill 

 27. 457 

 32. 482 

 34. 819 

 32. 566 

 42. 102 



8.98 



14.37 



9.71 



4.70 



14.36 



8.32 



8.21 



17.08 



10.23 



10.01 



14.65 



8.44 



1:4.6 



1909 



1:2.6 



1910 



14. 3 



1911 



1:9.9 



1912 



1:2.6 



1913 



1:4.5 



1914 



1:4.3 



1915 



1:1.6 



1916 



1:3.2 



1917 



1:3.5 



1918 



1:2.2 



1919 



1:5.0 







Average 



4.094 



5.640 



7.109 



8.361 



7.057 



4.878 



37. 139 



10.76 



1:3.5 







The average evaporation for the six months from April to Sep- 

 tember, inclusive, for the 12 years from 1908 to 1919 was 37.139 

 inches. The lowest total evaporation, 27.457 inches, was recorded in 

 1915, the year of the greatest rainfall during the same months. The 

 highest total evaporation, 46.701 inches, was recorded in 1911, the 

 year of the lowest seasonal rainfall. Thus the evaporation usually 

 varies inversely with the precipitation, though this is not always 

 the case^ 



' Briggs, L. .T., and Belz, J. O. Dry farming in relation to rainfall and evaporation. 

 U. S. Dept. Agr., Bur. Plant Indus. Bui. 188, p. 16-20. 1911. 



