YIELD OF SPRING WHEAT 13 



violation of fundamental requirements, the continued violation of 

 such requirements can only result in ultimate disaster, as has been 

 abundantly demonstrated in recent years. 



SUMMARY AND CONCLUSIONS 



Soil-moisture data at or near seeding time and the yields of spring 

 wheat are available for a total of 261 station years at 15 stations in 

 the Great Plains during the years 1907-38. With a few exceptions, 

 data were obtained on three methods of cultivation, the total number 

 of items being 765. 



The nonavailable water of each soil having been determined in 

 another study, 4 that knowledge was used to place each plot, or method, 

 each year in one of three categories: (1) Soil wet 1 foot deep or less, 

 (2) soil wet 2 feet deep, and (3) soil wet 3 feet deep or more, and the 

 yields were assembled according to this placement. 



Plot A, continuously cropped and spring-plowed, with 1 foot or less 

 of wet soil in the spring 30 percent of the time averaged 6.3 bushels. 

 With 2 feet of wet soil 44 percent of the time the average yield was 

 11.7 bushels, and with the soil wet 3 feet or more 26 percent of the 

 time the average yield was 15.5 bushels. 



The record of plot B continuously cropped and fall-plowed paralleled 

 that of plot A rather closely. With 1 foot or less of wet soil 35 percent 

 of the time the average yield was 6.7 bushels, with 2 feet of wet soil 

 38 percent of the time the average yield was 11.7 bushels, and with 3 

 feet or more of wet soil 27 percent of the time the average yield was 15.9 

 bushels. On plots C and D, alternately cropped and fallowed, an 

 initial condition of 1 foot or less of wet soil obtained only 5 percent of 

 the time, and the average yield from that condition was 6.9 bushels. 

 The crop started on 2 feet of wet soil 21 percent of the time and aver- 

 aged under that condition 12.6 bushels. The soil was wet 3 feet or 

 more deep 74 percent of the time, and the yields from this condition 

 averaged 19.9 bushels. 



Under the limited precipitation of the Great Plains, the initial water 

 content of the soil, which can be approximated by the depth to which 

 the soil is wet, is a strong determinant of the yield that will be produced. 



Frequent failures, low average yields, and very infrequent good 

 yields from spring wheat seeded on soil that is wet only 1 foot deep or 

 less clearly show that seeding when that condition exists is not war- 

 ranted. 



The results from seeding on soil wet 2 feet deep present a more fav- 

 orable picture, being intermediate between those obtained when the 

 initial depth of wet soil was either less or greater. Two feet of wet 

 soil may provide a satisfactory margin of safety in some localities, but 

 it does not in others. 



The highest assurance of good yields is afforded by an initial con- 

 dition of 3 feet or more of wet soil. This condition is much more 

 frequent on fallowed land than on land that bore a crop the preceding 

 year. The average yields from tins condition are markedly higher on 

 fallowed land than on continuously cropped land, chiefly because the 

 depth of wet soil is frequently greater. 



4 Unpublished data in the files of the Division of Dry Land Agriculture. 



