48 MISCELLANEOUS PUBLICATION 9 52. U.S. DEPT. OE AGRICULTURE 



These dryland stations provided 

 excellent opportunity to study 

 changes in soil nitrogen as in- 

 fluenced by different cropping sys- 

 tems over a wide range of soil and 

 climatic conditions. 



Purposes of this study were: (1) 

 to determine the effects of cropping 

 on the total nitrogen and carbon 

 contents of various dryland soils: 

 (2) to evaluate the relationship of 

 total nitrogen in the soil to the 

 capacity of that soil to produce 

 nitrate-nitrogen: and (3) to show 

 the influence of the changes in soil 

 nitrogen on crop yields. 



Changes in total nitrogen in the 

 surface 6 inches of soil at the 10 

 locations were tabulated (table 31). 



Average loss of nitrogen was 36 

 percent in 37 years. This was a 

 0.98-percent loss of nitrogen for 

 each year of cropping. Percentage 

 reduction in nitrogen content caused 

 by cultivation and cropping was 

 relatively constant, even though 

 there was wide variation in total 



nitrogen content of the virgin soils. 



Changes in organic carbon in the 

 surface 6 inches of soil at the same 

 10 locations were tabulated (table 

 32). 



Annual carbon loss averaged 1.17 

 percent over a 37-year period. 

 Cropping caused greater organic- 

 carbon losses than nitrogen losses. 



Nitrogen and carbon losses from 

 the 6- to 12-inch depth at Mandan. 

 Dickinson. Havre, Sheridan, Archer, 

 and Akron were also measured {27). 

 An average of 15 percent of the 

 nitrogen and 20 percent of the 

 carbon was lost during 35 years of 

 cropping. 



Losses of soil nitrogen and carbon 

 were measured for several small 

 grains (27). Haas and coworkers 

 found no indication that one small 

 grain influenced nitrogen and car- 

 bon losses more than any other. 



Percentage change in nitrogen 

 and carbon content of the surface 

 and subsurface soils in rotations 

 with and without green manures 

 were tabulated (tables 33 and 34). 



Table 31. — Total nitrogen in surface 6 inches oj virgin soils and soils 

 cropped tor an average oj 37 years and the total and per-year percentage 

 loss caused by cropping. 10 locations in the northern and central Great 



Plains 1 









Total nitrogen content 





Cropping 



Years 

 of 





















Location 



period 



crop- 







Loss 



Loss per 







ping 



\ irein 



Cropped 



with 



year of 









soils 



soils 



crop- 

 ping 



crop- 

 ping 







X umber 



Percent 



Percent 



Percent 



Percent 



Mandan. X. Dak 



1913-43 



30 



0. 160 



0. 116 



28 



0.93 



Dickinson. N. Dak 



1907-47 



40 



. 293 



. 149 



49 



1. 23 



Havre. Mont 



1916-47 



31 



. 151 



. 090 



40 



1. 29 



Moccasin. Mont 



190S-47 



39 



. 300 



.205 



32 



.82 



Sheridan. Wyo 



1917-47 



30 



. 159 



. 121 



24 



. SO 



Archer. Wyo 



1913-47 



34 



. 122 



.082 



33 



.97 



Akron. Colo 



190S-47 



39 



. 134 



.086 



36 



. 92 



Colbv. Ivans 



1905-46 



41 



. 165 



. 105 



36 



. SS 



Hays, Kans 



1903-46 



43 



. 220 



. 122 



45 



1. 05 



Garden City. Ivans 



1907-46 



39 



. 120 



.077 



36 



. 92 



Mean 





37 



0. 1S2 



0. 115 



36 



0. 98 



a from Haas and coworkers (27). 



