38 MISCELLANEOUS PUBLICATION 952. U.S. DEPT. OF AGRICULTURE 



hattan. One year's growth of 

 sweet clover reduced the subsoil 

 moisture to near the wilting point 

 to a maximum depth of 9 feet. 

 The growth of sweetclover for 1 or 

 2 years under limited rainfall condi- 

 tions may result in the development 

 of a dry layer of sufficient depth to 

 prevent utilization of moisture at a 

 lower level by subsequent alfalfa 

 crops. 



Chemical and Physical Effects of 

 Legumes and Grasses on Soils 



Nitrogen and carbon changes of 

 the soils have been measured period- 

 ically at the Hays, Colby, and 

 Garden City Branch Experiment 

 Stations (34, 35, 59). 



In 1943, Myers and coworkers 

 (59) reported on nitrogen and car- 

 bon changes in the 0- to 7-inch laver 

 of these soils during 1916-38. The 

 higher the nitrogen and carbon con- 

 tents of the soil in 1916, the greater 

 the loss of these elements during 

 this period. Cropping system 

 showed a definite relationship to the 

 loss of each element. Continuous 



small-grain production and alter- 

 nate small grain and fallow caused 

 relatively low losses. Continuous 

 row crops and alternate row crops 

 and fallow produced the greatest 

 losses. Rotations including row 

 crops and small grain produced 

 intermediate losses. 



In 1957, Hobbs and Brown (34, 

 35) reported on nitrogen and or- 

 ganic-carbon changes for 1916-46. 

 Nitrogen losses are curvilinear with 

 time; the greatest losses occurring 

 in the years immediately after sod 

 breaking (fig. 3). 



Although a new nitrogen equilib- 

 rium at each station was indicated, 

 apparently no location had reached 

 that equilibrium. Figure 3 indi- 

 cates that highest equilibrium will 

 be reached in the soils with the 

 highest original nitrogen content 

 (Hays) and the lowest equuibrium 

 in the soils with the lowest original 

 content (Garden City). 



Hobbs and Brown found that 

 green manure had differential effects 

 on nitrogen and carbon losses from 

 the surface soils at Havs, Colbv, 

 and Garden City (table 27). 



Table 27. — Losses of nitrogen and carbon from 0- to 6-inch soil depths with 

 various rotations at Hays, Colby, and Garden City, Kans., 1916-46 l 





Loss of nitrogen and carbon at — 



Rotation 



Hays 



Colby 



Garden City 





Nitro- 

 gen 



Carbon 



Nitro- 

 gen 



Carbon 



Nitro- 

 gen 



Carbon 



Continuous small grain 



Small grain, fallow 



Including rye green- 

 manure 2 . _ 



Percent 

 13. 5 

 13.4 



15. 4 



16. 6 

 31. 1 

 31.5 

 38.4 



Percent 

 25. 1 

 27. 7 



29.0 



29.4 

 37.4 

 42.0 

 51. 6 



Percent 

 12. 8 

 23.8 



26. 6 



Percent 

 21.3 

 27.8 



33. 8 



Percent 

 7.9 

 9. 8 



15. 5 



22.0 

 12. 5 

 30.9 

 27.7 



Percent 

 33.0 

 25. 



35. 1 



Including pea green- 

 manure 3 _ _ 



32. 9 43. 6 



37.4 



Fallow, wheat, sorghum 



Continuous row crop 



Row crop, fallow. _ 



25.0 

 27.0 

 29.9 



26.4 

 40. 4 

 44. 1 



34. 2 

 46.3 

 40. 







Mean _ 



22. 8 



34. 6 



25. 4 



33. 9 



18.0 



35. 8 















1 Data from Hobbs and Brown (85). 



2 Small grain, rye green-manure, small grain, row crop. 



3 Small grain, pea green-manure, small grain, row crop. 



