LEGUMES AND GRASSES 



25 



for soil moisture periodically from 

 May 12 to October 14, 1924. Both 

 plots were kept free of vegetation 

 during the period. During the 

 144-day period, rainfall measured 

 14.98 inches. On the check plot, 

 0.94 inches, or 6.3 percent, of the 

 rainfall was conserved. In the 

 manure-treated plot, 2.93 inches, 

 or 19.6 percent, of the rainfall was 

 conserved. Addition of the manure 

 tripled the conservation of rainfall. 



Russel (70) found that a high 

 organic-matter content was ad- 

 vantageous in dry weather and 

 detrimental in wet weather. High 

 organic matter was advantageous 

 during dry weather because it re- 

 duced soil cracking and lowered 

 evaporation losses. It was detri- 

 mental during wet weather because 

 reduced cracking slowed deep water 

 penetration. 



Tysdal and Kiesselbach (80) re- 

 ported that increased soil nitrate 

 production after alfalfa, in eastern 

 Nebraska, was favorable in seasons 

 of high rainfall but was often detri- 

 mental when rainfall was deficient. 

 In dry years, nonalfalfa land usually 

 yielded more, because the dimin- 

 ished vegetative growth was better 

 supported by the limited water 

 supply. In eastern Nebraska, the 

 yield increases more than offset the 

 yield depressions. The authors 

 concluded that overstimulation and 

 resultant crop "burning" were more 

 frequent in central and western 

 Nebraska. 



In 1946, McHenry and coworkers 

 (47) reported the carbon and nitro- 

 gen changes of a Chernozem soil as 

 affected by 1 to 9 years of perennial 

 grass. One of the purposes of this 

 study was to investigate the main- 

 tenance of soil organic-matter under 

 various periods of grass. The grass 

 was a mixture of western wheat- 

 grass, crested wheatgrass, and 

 bromegrass. The experiment was 

 conducted at North Platte on 

 Holdrege silt loam. 



Their findings show that, with 

 one exception, some loss of nitrogen 

 and carbon occurred, regardless of 

 the number of years in grass (table 

 16). On plots that had been in 

 grass more than 6 years, total 

 nitrogen and organic-carbon con- 

 tents were significantly greater than 

 the nitrogen and carbon contents 

 of the plots under continuous culti- 

 vation. 



The authors (47) concluded that 

 perennial grasses do not increase 

 organic-matter levels when includ- 

 ed in a cropping system at North 

 Platte. A continuous grass cover 

 barely maintained nitrogen and 

 carbon levels. 



McHenry and coworkers (50) 

 studied pore space and aggregation 

 on these same plots. There was no 

 significant difference in pore space 

 saturation related to previous years 

 in grass. Water-stable aggregates 

 were measured in the first cropping 

 year after the grass was plowed. 

 Water-stable aggregates increased 

 in the 1- to 3-inch depth as the 

 number of years in grass increased. 

 In the second cropping year, dif- 

 ferences in water-stable aggregates 

 were not related to years in grass. 

 During the first year of cropping, 

 the percentage of water-stable ag- 

 gregates in 1- to 3-inch depths was 

 correlated with organic matter. 

 Under the conditions of this ex- 

 periment, any effect that grasses 

 had on measured soil properties was 

 largely dissipated by the end of the 

 first cropping season. 



In 1956, the second 10-year cycle 

 of the grass experiments at North 

 Platte was completed. Mazurak 

 and coworkers (54) reported on the 

 effect of age of grass stand and the 

 application of nitrogen on the 

 plrysical properties of the soil. 

 This was a continuation of the study 

 reported by McHenry and co- 

 workers (47) in 1946. The main 

 study involved two grasses, inter- 

 mediate wheatgrass and brome- 



