46 MISCELLANEOUS PUBLICATION 952, U.S. DEPT. OF AGRICULTURE 



for 3 years and protein content was 

 increased for 8 years after plowing 

 the alfalfa sod. Nitrate production 

 capacity showed a sharp decline 6 

 years after the alfalfa sod was 

 plowed. 



Seeded grasses increased aggrega- 

 tion at Hays. Buffalograss was the 

 most effective of seven grasses 

 tested. The most rapid increase in 

 aggregation was brought about in 

 4 or 5 years. Twenty-eight years 

 of buffalograss restored aggregation 

 to the same level as native pasture. 

 How long this aggregation would 

 last when the grass sod is plowed is 

 unknown. 



Continuous wheat, stubbled-in 

 without tillage, showed greater soil 

 aggregation than other cropping 

 systems. However, yields from 

 stubbled-in wheat were too low to 

 be profitable. 



All cultivated plots at Hays 

 showed low aggregation in the 

 plow layer. 



Colorado 

 Yields 



In 1944, Brandon and Mathews 

 (3) published the results of dryland 

 rotations and tillage experiments at 

 the Akron (Colorado) Field Station 



for 1909-38. The soil is Kago silt 

 loam. Annual precipitation aver- 

 aged 17.1 inches. They tabulated 

 data on yields of winter wheat, 

 spring wheat, and oats after green- 

 manure fallow, continuous cropping, 

 and ordinary fallow (table 29). 



Crops after green-manure fallow 

 yielded less than crops on ordinary 

 fallowed land. Yields after the 

 green manures were related to the 

 moisture used by the green-manure 

 crop. Yields were highest after 

 winter rye, next highest after peas, 

 and lowest after sweetclover. Win- 

 ter rye was plowed under early; 

 peas and sweetclover were plowed 

 under about a month later than 

 winter rye. Sweetclover grew more 

 vigorously than peas and used more 

 soil moisture. Moisture limitations 

 prevented the crops from making 

 productive use of any greater fertil- 

 ity that resulted from green manur- 

 ing, because burning due to over- 

 stimulation was frequently evident. 



Second-and third-year yields after 

 green-manure crops were no higher 

 than those in rotations containing 

 ordinary fallow; usually they were 

 lower. 



In two 6-year rotations, brome- 

 grass and alfalfa were grown for 3 



Table 29. — Average yields of winter wheat, spring wheat, and oats after 

 green-manure fallow, continuous cropping, and ordinary fallow, Akron, 

 Colo., 1909-38 l 





A vera 



ge yield, per acre, undei 

 treatment- 



(previous crop or 



Crop 



Green-manure fallow 



Continuous 

 cropping 



Ordinarv 





Rye 



Pea 



Sweet- 

 clover 



fallow 



Winter wheat. _ _ _ _ 



Bushels 

 11.4 



7.7 

 20.3 



Bushels 

 9.0 

 6.8 

 17.9 



Bushels 



~~5.~9~ 

 15.6 



Bushels 

 7. 1 

 7.8 

 16.3 



Bushels 

 16.3 



Spring wheat __ __ 



10.2 



Oats_ _ _ _ _ 



27. 7 







Data from Brandon and Mathews (5). 



