YIELD OF SPRING WHEAT H 



26 percent of the years on A and 27 percent on B; but 3 feet or more 

 of wet soil obtained in 74 percent of the years on the fallowed plots 

 C and D. The yields averaged 15.5 bushels on A, 15.9 bushels on B, 

 and 19.9 bushels on C and D. These yields were 246, 237, and 

 2S8 percent, respectively, of the yields obtained from the same plots 

 in the years when the available water in the spring was limited to the 

 first foot of soil. The higher yield on the summer-fallowed plots than 

 on the continuously cropped plots will be noted. The explanation for 

 most of the increase is to be found in the fact that the summer-fallowed 

 land contained available water below the third foot more often than 

 did the continuously cropped plots. The authors have presented evi- 

 dence on this point in another publication U,p. 65). With only 1 foot 

 or 2 feet of wet soil the average yield was only slightly higher on the 

 fallowed plots than it was on the continuously cropped plots. 



On land continuously cropped to small grain 2 feet of wet soil in 

 the spring was a somewhat more frequent condition than either one of 

 the other conditions, 1 foot or 3 feet of wet soil. The stated condition 

 existed in 44 percent of the total years on plot A and 38 percent on 

 plot B . On the summer-fallowed plots its occurrence fell to 2 1 percent. 

 The yields as a class were intermediate, but on the continuously 

 cropped plots they were somewhat closer to those on 3 feet of wet soil 

 than to those on 1 foot. On continuously cropped land about 48 

 percent of the crops that were started on 2 feet of wet soil yielded 10 

 bushels or more, about 33 percent yielded 15 bushels or more, and 

 about 22 percent yielded 20 bushels or more. On fallowed land the 

 percentages were 58, 40, and 20, respectively, but 2 feet of wet soil 

 in the spring occurs only about half as frequently on fallowed land as 

 on land that is cropped each year. 



At some stations, which is to say with some soils and precipitations, 



2 feet of wet soil in the spring seems to be a fairly adequate condition , 

 but at some other stations it does not provide a sufficient margin of 

 safety or a level of production high enough to warrant seeding when 

 that condition obtains. 



It is not a primary purpose of the authors to present in this circular 

 a study of cultivation methods or cropping systems as such, but it is 

 impossible to avoid a comparison of alternate summer fallowing with 

 continuous cropping to wheat. As averages of all stations and years, 

 the crop on land that grew wheat every year began its growth about 



3 years out of 4 on soil that was wet not more than 2 feet deep and only 

 1 year out of 4, on soil that was wet 3 or more feet deep. When 

 seeded on land that had been summer fallowed the previous year, 

 these figures were reversed and 3 years out of 4 the crop enjoyed the 

 benefits of 3 or more feet of wet soil, and only 1 year in 4 was compelled 

 to start on soil that was wet to a depth of 2 feet or less. The effects 

 of these conditions on yields have already been shown. 



The high frequency of an inadequate initial supply of soil water 

 following a crop of wheat and the subsequent frequent failures or low 

 yields and the generally low average yields that result from continu- 

 ous cropping to wheat make this an entirely unwarranted practice at 

 some stations, and at the best a questionable one at others where soil 

 and precipitation are more favorable. 



The high risk of failure attending the seeding of a grain crop when 

 the stored water is not sufficient to have penetrated to a depth of 

 more than 1 foot raises the question of what should be done when that 



