EFFECT OF FALL IRRIGATION ON" CROP YIELDS. 



The figures in Table IV show that in 1914 the yields of wheat, 

 barley, and corn were higher on the fall-irrigated plats than on the 

 check plats, the increases being 37, 2, and 1 per cent, respectively, 

 while the yields of the four other crops were lower on the fall-irrigated 

 land, and that the average yield increase of the seven crops in that 

 year was 2 per cent in favor of fall irrigation. In 1915 the yields of 

 all the crops were lower on the fall-irrigated land, the average decrease 

 being 11 per cent. In 1916 all the crops yielded less on the fall- 

 irrigated plats than on the checks, except potatoes, which yielded 5 per 

 cent more. In the 3-year average, wheat on fall-irrigated land showed 

 an increase of 10 per cent, while all the other crops showed decreases 

 ranging from 3 to 10 per cent, the average yield decrease of the seven 

 crops on fall-irrigated land for the 3-year period being 4 per cent of 

 the average yield of the check plats. 



The fact that of the 42 duplicate plat averages secured in the 3-year 

 period only four were in favor of fall irrigation would support a pre- 

 sumption that fall irrigation on this soil was detrimental. However, 

 since not all the yields were against fall irrigation, it is possible that 

 the yield variations were accidental. In order to determine whether 

 these differences were significant, the probable errors of the average 

 yields have been calculated. The results are shown in Table V, in 

 which the yields secured during the 3-year period are summarized. 



Table V. — Summary of the yields secured in the fall-irrigation experiments at the Belle 

 Fourche Experiment Farm in 1914, 1915, and 1916, showing the probable errors of the 

 averages. 





Unit of 

 yield. 



Fall-irrigated plats. 



Check plats. 





Crop. 



Num- 

 ber of 

 plats 

 aver- 

 aged. 



Average 



yield per 



acre. 



Num- 

 ber of 

 plats 

 aver- 

 aged. 



Average 



yield per 



acre. 



Difference 



in favor 



of fall 



irrigation. 



Wheat 



Bushels... 

 ...do 



6 

 6 

 6 

 6 

 6 

 6 

 6 



22. 1± 2.2 

 61. 9± 5.0 

 33. 9± 1.5 

 13. 7± 1.4 

 42. 2± 3.3 

 8.4± 1.1 

 167 ±23.0 



6 

 6 

 6 

 6 

 6 

 6 

 6 



20. 1± 1.4 

 67. 8± 6.0 

 36. 1± 2.5 

 15. 2± .9 

 43. 9± 3.1 

 9.2± 1.1 

 172 ±19.0 



+2. 0± 2.6 





— 5.9± 7.8 



Barley 



...do 



— 2. 2± 2.9 



Max 



...do 



— 1.5± 1.7 





...do... 



— 1.7± 4.5 





Tons 



Bushels... 



— .8± 1.5 





— 5.0±30.0 







The figures in the last column in Table V show for each of the seven 

 crops the difference between the average yield of the fall-irrigated 

 plats and that of the check plats during the 3-year period. None of 

 the differences was as great as the probable error, so that all must 

 be regarded as insignificant. A similar tabulation of the yields of 

 straw and stover (which are not shown here) produces a like result, 

 there being no significant differences in the average yields of these 

 products. 



The explanation of the somewhat lower average yields secured on 

 the fall-irrigated land lies in the relatively low productivity of Series 



