10 



CIRCULAR 5 6 3, IT. S. DEPARTMENT OF AGRICULTURE 



Table 2. — Summary of number of years and average yields of each of three methods 

 at all stations when the soil was wet to the depth specified 





Soil wet to— 



Total 

 years 





Plot and treatment 



1 foot or less 



2 feet 



3 feet or more 



Average 

 yield i 





Years 



Yield 



Years 



YieH 



Years 



Yield 





A, continuously cropped 



B, continuously cropped 



C and D, alternately fallowed.. 



Number 

 79 

 87 

 12 



Bushels 

 6.3 

 6.7 

 6.9 



Number 

 114 

 93 

 55 



Bushels 

 11.7 

 11.7 

 12.6 



Number 

 68 

 66 

 191 



Bushels 

 15.5 

 15.9 

 19.9 



Number 

 261 

 246 



258 



Bushels 

 11.1 

 11.0 

 17.7 



Total or average ' 



178 



6.5 



262 11.9 



325 



18.2 



765 



13.3 



Weighted averages. 



25 



20 



CD 



O 10 



H 0- 



LlI _ 



5P| 



UJ 



i-u. 2 



SPRING PLOWED, 



CONTINUOUSLY 



CROPPED 



?™4 



^4 



6.3 \ 



L 



i 



H8fl 



p™4 



11.7 \ 



15.5 



FALL PLOWED, 



CONTINUOUSLY 



CROPPED 



%~JX 



SVW* 



^™4 



6.7 ! 



35 



_J. 



1.7 1 



38 



15.91 



Ms 



27 



FALLOWED, 



ALTERNATELY 



CROPPED^ 



p™4 



6.9 \~ 



P™4 



12.6 



\ ' ..': 



19.9 ! 

 S 



~~ 



1 



7« 



Figure 2. — Average yields of spring wheat at 15 field stations in the Great Plains 

 when the soil was wet to different depths in the spring on three methods of prep- 

 aration. (The figures in the depth blocks show the percentage of years when 

 that condition obtained.) 



The data cover a total of 261 station years on plot A, 246 years on 

 plot B, and 258 years on plots C and D, a total of 765. The two con- 

 tinuously cropped plots, A, spring-plowed, and B, fall-plowed, are 

 essentially duplicates for the purpose of this study when compared 

 with the pair of plots, C and D, which are alternately cropped and 

 fallowed. 



The soil was wet in the spring to a depth of only 1 foot or less in 

 30 percent of the years on plot A, 35 percent on plot B, and only 5 per- 

 cent on C and D. The average yields from this condition were 6.3, 

 6.7, and 6.9 bushels per acre, respectively. Yields of 15 bushels or 

 more per acre were obtained but 12 times on plot A and 15 times on plot 

 B (table 3). There has been less than 1 chance in 6 of producing a 

 good crop when the depth of wet soil in the spring did not exceed 

 1 foot. 



The soil was wet to a depth of 3 feet or more slightly less often 

 than it was wet only 1 foot or less on the continuously cropped plots, 



