LEGUMES AND GRASSES 



11 





be required to reduce the carbon 

 and nitrogen losses to zero. Resi- 

 dues and manure were equally 

 effective in the long-term mainte- 

 nance of soil nitrogen and carbon 

 contents. Manure applications 

 were approximately equal to the 

 manure that would have been pro- 

 duced by feeding the corn, oats, 

 and clover raised on the land. 



Physical soil measurements did 

 not show any important changes in 

 Fargo clay that could be related to 

 past management practices. Tilth 

 apparently had not declined enough 

 in any of the plots to limit yields, 

 as evidenced by high yields of corn, 

 wheat, oats, and barley when 

 treated with adequate amounts of 

 nitrogen and phosphorus fertilizer. 

 Since soil tilth had not deteriorated 

 to any extent on Fargo clay, the 

 authors postulated that poor tilth 

 would be a minor problem in 

 coarser textured cultivated soils 

 under Fargo climatic conditions. 



Summary 



Legumes and grasses used as 

 green manures and hay or pasture 

 crops frequently depressed yields 

 of crops that immediately followed, 

 owing to the dry soil conditions 

 in which the legumes and grasses 

 left the soil. 



Nitrogen-fertilized grasses gen- 

 erally increased the nitrogen and 

 carbon content of the soil to some 

 extent. Unfertilized grass main- 

 tained nitrogen and carbon. Leg- 

 umes added some nitrogen and 

 carbon. 



Nitrogen fertilizer appeared to be 

 more efficient than legumes in in- 

 creasing crop yields. 



Use of manure and crop residues 

 on Fargo clay soil reduced the rate 

 of loss of plant-available nitrogen 

 and phosphorus. Data indicated 

 that about four times the residue 

 now being returned to the soil 

 would be needed to maintain car- 



bon and nitrogen contents of the 



Fargo soil. 



South Dakota 

 Yields 



Green-manure experiments were 

 started at Newell and Ardmore, 

 S. Dak., in 1909 and 1913, respec- 

 tively {1 1 , 51 , 65) . Yields of wheat 

 and oats after green-manure fal- 

 low, continuous cropping, ordinary 

 fallow, alfalfa, and bromegrass are 

 presented (table 7). 



In 1927, Cole and coworkers (11) 

 reported that green-manure fallow 

 and ordinary fallow produced simi- 

 lar yields of spring wheat at Ard- 

 more (table 7). Green-manure 

 fallow lowered yields of winter 

 wheat. In 1937, Mathews and 

 Ciark (51) reported that oats on 

 green-manure fallow produced lower 

 grain yields than on ordinary fallow 

 (table 7). No cumulative benefit 

 from plowing under green-manure 

 crops was shown. Any increase in 

 fertility brought about by plowing 

 under a green-manure crop was 

 counterbalanced by the loss of 

 moisture in producing the green 

 manure. Annual precipitation 

 averaged 15.8 inches at Ardmore. 



Two grain crops, oats and flax r 

 were grown on land plowed out 

 of alfalfa, bromegrass, and clover 

 for a 20-year period (51). Yields 

 of oats after alfalfa, bromegrass, and 

 sweetclover averaged 20, 23, and 

 27 bushels per acre, respectively 

 (table 7). Yields of oats after 

 fallow and continuous cropping 

 averaged 38 and 23 bushels per 

 acre, respectively. Average yield 

 of oats after any sod crop was less 

 than that after fallow — the re- 

 duction in yield being especially 

 sharp after alfalfa and bromegrass. 

 These two crops left the soil so dry 

 that the succeeding crop suffered 

 from drought. 



Depressing effect on crops after 

 sod sometimes extended into the 



