LEGUMES AND GRASSES 



9 



in soil nitrogen. The nonharvested- 

 plot gains were greater than the 

 harvested-plot gains. 



In 1958, Haas (25) reported a 

 5-year study on the soil-improving 

 effects of six grasses and alfalfa at 

 Mandan. His study indicates that 

 the total weight of roots increased 

 until the grass stands were about 

 4 years old. After 4 years, there 

 was little change in total weight 

 of roots. Crested wheatgrass, 

 bromegrass, Russian wildrye, and 

 western wheatgrass produced more 

 root weight than did green needle- 

 grass and Canada wildrye. 



Haas determined root residues 

 1& 2%, S%, and 4% years after the 

 sod was plowed. Less than 25 

 percent of the grass-root residue 

 remained in the 0- to 6-inch depth 

 2Y 2 years after plowing. Approxi- 

 mately 500 pounds per acre of 

 threadleaf sedge (Car ex filijolia 

 Nutt.) roots were recovered in 

 the upper 12 inches of soil. These 

 roots had persisted in the soil 

 since the land was plowed from sod 

 35 years earlier. Threadleaf sedge 

 deserves a special study to deter- 

 mine root production, persistence, 

 and effect on soil structure. 



In a separate study one manure 

 and seven commercial fertilizer 

 treatments were broadcast annually 

 on crested wheatgrass, Russian 

 wildrye, and bromegrass (25). 

 Nitrogen increased root weights of 

 all three species. Phosphorus in- 

 creased root weights at the 60- 

 pound rate; potassium had no 

 effect. Annual applications of 15 

 tons of manure had the same effect 

 on root production as 30 pounds of 

 nitrogen. 



Nitrogen and carbon changes 

 were measured after 5 years of 

 grass or legumes without fertiliza- 

 tion (table 5). Hay crops were 

 removed annually. 



Haas' data indicate that there 

 was little change in the nitrogen 

 content of the soil from the 0- to 

 6-inch depth under grass or alfalfa. 

 In the 6- to 12-inch depth there 

 were both losses and gains with the 

 grasses. Substantial nitrogen losses 

 from the 12- to 24-inch depth oc- 

 curred in all plots. No explanation 

 of this loss was given. Organic- 

 carbon content increased for all 

 depths under all plots of grass and 

 alfalfa except crested wheatgrass 

 and green needlegrass. The in- 



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

 years of grass or alfalfa without fertilization, Mandan, N. Dak. 1 



Species 



Gain or loss of nitrogen 

 at depth (inches) of — 



Gain or loss of carbon at 

 depth (inches) of — 





to 6 



6 to 12 



12 to 24 



Oto G 



6 to 12 



12 to 24 



Crested wheatgrass 



Green needlegrass __ 



Percent 

 

 -2 

 + 1 

 

 -2 

 + 2 



Percent 

 -6 

 -5 

 -2 



+ 2 

 + 7 

 + 9 



Percent 

 -6 



— 7 

 -8 

 -5 

 -7 

 — 11 



Percent 



+ 4 

 -1 

 + 1 

 + 1 

 + 3 

 + 5 



Percent 

 -4 

 -2 



+ 2 



+ 4 



+ 12 



+ 18 



Percent 

 

 



Western wheatgrass 



Canada wildrye 



+2 



+ 1 



Russian wildrye _ _ 



+ 7 



Bromegrass 



+ 4 







Mean _ 





 + 1 



+ 1 

 + 3~ 



-7 

 -8 



+ 2 

 + 2 



+ 5 

 + 12 



+ 2 



Alfalfa 



+ 1 







i Data from Haas {25). 



