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



creases were quite large in the 6- to 

 12-inch depths under Russian wild- 

 rye and bromegrass. Results show 

 that 5 years of grasses and alfalfa 

 were effective in maintaining the 

 nitrogen and carbon content of the 

 surface soil. 



Nitrogen and carbon changes 

 were measured 5 years after the 

 sod was plowed (table 6). Corn 

 and small grains were grown during 

 this period. 



His data indicate that losses of 

 soil nitrogen, after plowing the sod, 

 occurred in most of the grass plots. 

 The average loss was 3 percent from 

 the 0- to 12-inch depths and 7 per- 

 cent from the 12- to 24-inch depths. 

 The net effect of the 10-year period 

 (5 years in sod followed by 5 years 

 in a rotation of corn and small 

 grain) was a slight loss of nitrogen 

 and a slight gain in carbon. 



For the alfalfa plots, small nitro- 

 gen gains occurred in the 0- to 12- 

 inch depth and there was a 5 per- 

 cent loss in the 12- to 24-inch depth. 

 During the same period, losses of 

 soil nitrogen in a rotation of wheat 

 and corn were 6, 12, and 8 percent, 



respectively, for the three depths. 



Young and coworkers (84) re- 

 ported on the laboratory phases of 

 a study to evaluate the effective- 

 ness of 40 years of soil-management 

 practices in maintaining fertility of 

 Fargo clay at Fargo. They com- 

 pared livestock- and grain-farming 

 systems. The livestock-farm rota- 

 tion consisted of wheat, clover, oats, 

 and corn. The straw, corn fodder, 

 and clover hay were removed. 

 Manure — 7 to 10 tons per acre — 

 was applied before plowing for 

 corn. The grain-farm rotation con- 

 sisted of wheat, clover, barley, and 

 potatoes. Corn replaced potatoes 

 in 1944. Crop residues and second 

 growth of clover were returned to 

 the soil. 



Their findings show that total 

 nitrogen and organic-carbon con- 

 tent of the soil declined in all plots 

 and both rotations. Soil organic 

 carbon and nitrogen declined 27 

 percent in check plots and 20 per- 

 cent in residue and manure plots. 

 Results indicated that four times 

 the amount of manure or residue 

 now being returned to the soil may 



Table 6. — Changes in nitrogen and carbon contents, by soil depths, 5 years 

 after grass and legumes were plowed, Mandan, N. Dak. 1 



Species or rotation 



Gain or loss of nitrogen 

 at depth (inches) of — 



Gain or loss of carbon 

 at depth (inches) of — 





Oto 6 



6 to 12 



12 to 24 



Oto 6 



6 to 12 



12 to 24 



Crested wheatgrass 



Western wheatgrass 



Canada wildrye _ _ 



Percent 

 -G 





 -2 





 — 5 



Percent 

 -8 



+ 1 

 -5 

 -6 



+ 1 



Percent 

 -4 

 -6 

 -8 

 -12 

 -6 



Percent 



-7 

 + 1 

 + 2 

 + 1 

 -6 



Percent 

 -6 





 -2 

 -4 



+ 4 



Percent 



+ 1 

 + 1 

 + 3 



Russian wildrye 



Bromegrass __ 



-6 



+ 2 







Mean __ 



-3 



-3 



— 7 



-2 



-2 











Alfalfa 



+ 1 

 -6 



+ 4 

 -12 



-5 



-8 



+ 2 

 -4 



+ 12 

 -14 



-3 



Wheat, corn 



-2 







Data from Haas (25). 



