LEGUMES AND GRASSES 



23 



experiment showed that lime was 

 needed for optimum sweetclover 

 growth, which in turn would have 

 added to soil productivity for fol- 

 lowing crops. Other experiments 

 in the Corn Belt indicate that 40 

 pounds of nitrogen probably was 

 not sufficient for optimum produc- 

 tion of corn in this experiment. The 

 authors indicated that the amount 

 of supplementary nitrogen needed 

 for most profitable production 

 varied with growth and frequency 

 of the legume in the rotation. 



So/7 Moisture Use by Legumes and 

 Grasses 



In 1929, Kiesselbach and co- 

 workers (41) reported that the 

 productivity of alfalfa meadows 

 declined abruptly 4 to 5 years after 

 seeding at Lincoln, even though a 

 good stand remained. This was 

 attributed to depletion of subsoil 

 moisture. A 2-year stand of al- 

 falfa used subsoil moisture to a 

 depth of 25 feet. A 6-year stand 

 used moisture to 33 feet. Annual 

 precipitation averaged 27.8 inches. 



Their findings show that, with 

 ordinary cropping, natural restora- 

 tion of subsoil moisture after alfalfa 

 was very slow. During 15 years 

 of cropping to cereal crops after 

 plowing an established alfalfa 

 meadow, very little moisture ac- 

 cumulated below the 7-foot level. 

 This indicated that cereal crops 

 after alfalfa used all precipitation 

 and no water was stored in the deep 

 subsoil or lost to percolation at 

 Lincoln. 



In 1934, Kiesselbach and co- 

 workers (39) reported on restoration 

 of subsoil moisture at Lincoln by 

 several cultural treatments after 

 depletion by alfalfa meadows. 

 Cropping to corn, oats, and wheat 

 for 5 years restored only 0.1 inch of 

 moisture to the 6- to 15-foot depth. 

 Continuous corn for 5 years restored 

 3.1 inches, and continuous fallow 



711-108—64 4 



restored 13.2 inches of moisture to 

 the 6- to 15-foot level. After 1,2, 

 3, 4, and 5 years of continuous 

 fallow, the soil was wet to field 

 capacity to depths of 4, 7, 8, 9, 

 and 11 feet, respectively. Annual 

 precipitation for this period aver- 

 aged 1.4 inches below normal. 



After depletion of subsoil mois- 

 ture, there was no material change 

 in deep subsoil moisture during 5 

 years when alfalfa, sweetclover, and 

 red clover were on the land. These 

 crops were equally ineffective in 

 restoring moisture. Five years of 

 sweetclover or red clover did not 

 deplete deep soil moisture reserves 

 below 6 feet. 



Chemical and Physical Effects of 

 Legumes and Grasses on Soils 



In 1929, Russel (70) discussed 

 organic-matter problems under dry- 

 farming conditions. After dryland 

 was broken up, there was a gradual 

 disappearance of fiber and degranu- 

 lation of structure. This produced 

 an increased tendency toward ero- 

 sion by wind and water. Tillage 

 power requirements were also 

 increased. 



He found that dryland crops 

 tended to fire for several years after 

 alfalfa was plowed up. This he 

 attributed to excess nitrate pro- 

 duction, which led to rapid growth 

 and premature exhaustion of limited 

 soil moisture. Farm manures were 

 observed to do the same thing. 

 Sweetclover did not cause so serious 

 detrimental effects on subsequent 

 crops as alfalfa. 



Russel (70) conducted an experi- 

 ment at Lincoln to determine the 

 effect of increased organic-matter 

 content on intake and conservation 

 of rainfall. Forty tons per acre of 

 well-rotted manure were incorpo- 

 rated into a clay loam surface soil 

 on a uniform slope of 2 percent. 

 An adjacent plot was used as a 

 check. The two plots were sampled 



