LEGUMES AND GRASSES 



47 



consecutive years followed by oats, 

 corn, and spring wheat (table 30). 

 Oat yields after 3 years of alfalfa 

 and bromegrass were reduced when 

 compared with yields after 3 years 

 of wheat; the reduction probably 

 was caused by dry soil conditions. 

 The second and third crops after 

 alfalfa and bromegrass also were 

 reduced. 



The authors concluded that grass 

 should be grown for an indeter- 

 minate period rather than be made 

 a definite part of rotations. 



Summary 



Yields of winter wheat, spring 

 wheat, and oats after green-manure 

 fallow were substantially lower than 

 those after ordinary fallow. The 

 second and third crops after green 

 manures tended to yield less than 

 those in comparable rotations with 

 fallow. 



Bromegrass and alfalfa grown for 

 3 years reduced the yields of oats, 

 corn, and spring wheat that were 

 grown during the succeeding 3 

 years. 



Table 30. — Average grain yields of oats, corn, and spring wheat in alfalfa, 

 bromegrass, and nonsod rotations, Akron, Colo., 1909-88 1 





Average yield, per acre, for — 



Previous 3-year crop 



First 

 crop, 

 oats 



Second 

 crop, 

 corn 



Third 



crop, spring 



wheat 



Bromegrass __ 



Bushels 

 12. 

 12. 1 

 16. 4 



Bushels 

 7.8 

 8.5 

 10.6 



Bushels 



5. 8 



Alfalfa 



6. 6 



Wheat. __ 



8. 8 







Data from Brandon and Mathews (3). 



CARBON AND NITROGEN CHANGES IN SOILS AT 10 

 DRYLAND EXPERIMENT STATIONS 



In 1957, Haas and coworkers 

 (27) reported on the nitrogen and 

 carbon changes of soils from 17 

 experiment stations in the Great 

 Plains. Ten of these stations were 

 in the northern and central Great 

 Plains. The stations were estab- 



lished in the early part of the 20th 

 century to study the effects of 

 different rotations and tillage prac- 

 tices on crop production under 

 dryland conditions. The following 

 list shows the designations and 

 locations of the 10 stations. 



Experiment Station: Location 



United States Northern Great Plains Field Station Mandan, N. Dak. 



Dickinson Substation Dickinson, N. Dak. 



North Montana Branch Station Havre, Mont. 



Central Montana Branch Station Moccasin, Mont. 



Sheridan Substation Sheridan, Wyo. 



Archer Substation Archer, Wyo. 



United States Akron Field Station Akron, Colo. 



Colby Branch Station Colby, Kans. 



Fort Hays Branch Station Hays, Kans. 



Garden City Branch Station Garden Citv. Kans. 



