LEGUMES AND GRASSES 



59 



most medium- and fine-textured 

 cultivated soils of the northern and 

 central Great Plains. 



Data are inadequate, but it seems 

 probable that subhumid sandy lands 

 are the only cultivated areas in the 

 northern and central Great Plains 

 where water may be moving to the 

 water table. Some of the sandy 

 cultivated soils of northeastern Ne- 

 braska and the Great Bend area of 

 Kansas are probably losing some 

 precipitation to the water table. 

 Alfalfa would be a good crop to 

 grow to make use of this water. 

 Sweetclover has been shown to use 

 soil moisture to 9 feet in 1 year and 

 14 feet in 2 years. Grasses are 

 comparatively shallow rooted and 

 seldom deplete soil moisture below 

 6 feet. 



When grown for several years, 

 grasses maintain or may increase 

 soil nitrogen and organic matter. 

 Nitrogen applications may increase 

 nitrogen buildup, but seem to have 

 little effect on accumulation of 

 organic matter. Alfalfa grown for 

 several years usually increases soil 

 nitrogen and organic matter. 

 Where legumes and grasses are 

 grown for less than 1 year, chemical 

 and plrysical soil effects are usually 

 not measurable. 



Several dryland experiment sta- 

 tions have grown legumes and grass 

 for 3 years in 6-year rotations. 

 Nitrogen and carbon losses from the 

 soil have been reduced compared 

 with nonlegume, grass rotations. 

 Keductions in nitrogen losses were 

 due to reduced runoff and erosion 

 and to legume-nitrogen additions. 



Sweetclover, field peas, and rye 

 have been used in a green-manure 

 fallow system once in 4 years at 

 several dryland experiment stations 

 in the northern and central Great 

 Plains. Compared with non-green- 

 manure cropping systems, nitrogen 

 and carbon losses from the soil were 

 not significantly reduced. 



When grown for several years, 

 grasses decrease bulk density of the 

 surface soil, increase infiltration, 

 improve aggregation, and reduce 

 erosion. Effect of legumes on the 

 physical condition of the soil ap- 

 pears to be minor. Fourteen years 

 of sweetclover, fallow rotation at 

 Hays, Kans., did not increase sur- 

 face-soil aggregation appreciably. 



Data from Kansas, Nebraska, 

 North Dakota, and southwestern 

 Saskatchewan indicate that 3 to 5 

 years of grass substantially im- 

 proves soil structure. In south- 

 western Saskatchewan, crested 

 wheatgrass had a beneficial effect on 

 coarse- and medium-textured 

 soils, but it had little effect on 

 fine-textured soils. Data from 

 Hays, Kans., indicate that 25 to 30 

 years of buffalograss are necessary 

 to restore aggregation of a culti- 

 vated soil to the same level as native 

 pasture. Limited tests in Nebraska 

 and Kansas indicate that buffalo - 

 grass is one of the best grasses for 

 soil-aggregate formation and sta- 

 bility. 



Beneficial effects of grass appear 

 to be rather shortlived. Data from 

 Mandan, N. Dak., indicate that 75 

 to 95 percent of grass roots in the 

 surface 6 inches of soil had decom- 

 posed 2% 3'ears after plowing. At 

 Lincoln, Nebr., water-stable aggre- 

 gation for all grasses except buffalo- 

 grass had decreased 70 percent 2 

 years after plowing. Buffalograss 

 aggregation decreased 50 percent. 

 Structural improvement under grass 

 appears to be considerably slower 

 than structural deterioration after 

 the grass is plowed. 



Improved soil physical condi- 

 tions have seldom increased crop 

 yields in the northern and central 

 Great Plains. This probably in- 

 dicates that physical conditions are 

 not limiting crop production. 



Legumes and grasses are effec- 

 tive in reducing wind and water 

 erosion. Decomposing legume and 



