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



Table 14. — Average yields of wheat and corn in various 12-year rotations, 

 North Platte, Nebr., 1937-59 l 





Average yield, per acre, in — 



Rotation 



First cycle 



Second cycle 





Wheat 



Corn 



Wheat 



Wheat 



Corn 



Wheat 



4 years weeds 2 



4 years bromegrass 2 



4 years sweetclover 2 



Check 3 



Bushels 

 32 

 29 

 27 



29 



Bushels 

 32 

 31 

 32 

 24 



Bushels 

 14 

 13 

 14 

 12 



Bushels 

 30 

 32 

 29 

 29 



Bushels 

 29 

 32 

 31 

 27 



Bushels 

 12 

 12 

 12 

 12 







' Data from Ramjg, see footnote 6, below. 



2 Rotations included 4 years of weeds, bromegrass, or sweetclover followed by 8 years of fallow, wheat, corn, and 

 wheat. 



3 Fallow, wheat, corn, wheat rotation. 



grain was mature. Each year the 

 straw production was greater on the 

 10-year green-manured plot than 

 that on the 10-year fallowed plot. 



After 10 years of continuous 

 green manuring and fallowing, the 

 green-manure plot, at the 0- to 12- 

 inch soil depth, had 42 percent 

 greater carbon content and 19 

 percent greater nitrogen content 

 than the fallow plot. 



In 1960, Kamig 6 reported the 

 yields of wheat and corn (table 14) 

 in rotations containing sweetclover, 

 bromegrass, and weeds at North 

 Platte. The soil was Holdrege- 

 Goshen silt loam. 



His data indicate that wheat 

 yields after fallow during the first 

 cycle were highest after weeds and 

 lowest after sweetclover. Abun- 

 dant nitrogen from the sweetclover 

 resulted in vegetative overstimula- 

 tion and decreased grain yields 

 when the moisture supply was ex- 

 hausted before maturity. Corn 

 yields were notably lower for the 



6 Ramig, R. E. conservation crop- 

 ping SYSTEMS FOR THE CENTRAL GREAT 



plains. Paper presented at ARS-SCS 

 Research Application Workshop, Rapid 

 Citv, S. Dak., Feb. 16-17, 1960. (Mimeo. 

 Rpt.) 



check treatment. Results to 1959 

 indicated that grasses and legumes 

 in dryland rotations have little 

 effect on grain yields. Wheat- 

 protein data indicated temporary 

 increases in soil nitrogen after 

 sweetclover. 



Legume Versus 

 Sources 



Inorganic Nitrogen 



Kiesselbach and Lyness (40) re- 

 ported the results of crop-rotation 

 experiments at Lincoln for 1942-51. 

 The soil was Sharpsburg silty clay 

 loam. When these experiments 

 were initiated in 1933, lime and 

 commercial fertilizer were not 

 included as treatments. 



In 1951, all the grain plots except 

 barle} r were divided in half in four 

 of the rotations. One-half of each 

 plot was topdressed with nitrogen 

 at the rate of 40 pounds per acre. 

 These plots had never been limed. 



The 40-pound application of 

 nitrogen increased the yields of all 

 crops except the manured-wheat 

 crops (table 15). Data indicated 

 that sweetclover did not supply 

 adequate nitrogen for any crop in 

 the 6-year rotations. Results 

 (table 15) might have been different 

 had lime been used. A nearby 



