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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



than prairie sandreed (Calamovilfa longifolia 

 [Hook.] Scribn.) or needle-and-thread (Stipa 

 comata Trin. & Rupr.). The steers traveled an 

 average of 2.4 km. per 15-hour period in a 22-ha. 

 pasture grazed lightly, and 3.2 km. in those 

 grazed moderately and heavily. Brown and 

 Schuster (J) also reported detrimental effects of 

 trampling by livestock on hardland soils in the 

 southern High Plains. Comparison of penetrom- 

 eter readings showed 6 times as much compac- 

 tion on grazed as on ungrazed areas. They found 

 the compaction to be indirectly influenced by re- 

 duction in organic matter in the surface soil 

 brought about by prolonged heavy grazing. Bulk 

 density of the surface soil was 0.996 gm./cc. on 

 the ungrazed area and 1.180 gm./cc. on the grazed 

 urea. No difference in bulk density was found 

 between grazed and ungrazed areas on a high 

 elevation cattle range in Utah in early summer 

 before grazing and in late summer after grazing 

 (28). However, bulk density increased in both 

 grazed and ungrazed areas during the summer. 

 This was attributed to change in soil moisture. 

 In early summer, soils were moist and swollen, 

 thus they weighed less per unit volume than they 

 did when dry late in the summer. Greater bulk 

 density of grazed compared with ungrazed areas, 

 with little difference due to intensity of grazing, 

 has been reported by others (27, 32, 40. 43. U). 



Increase in runoff and erosion as grazing in- 

 tensity increased has been reported (1, 29, 34, 46)- 

 Infiltration and runoff are closely related; the 

 factors which restrict infiltration induce runoff. 

 Lusby (29) studied four grazed watersheds on 

 salt-desert range near Grand Junction. Colorado. 

 He found that cover remained about the same 

 over a 14-year period without grazing, but the 

 amount of bare soil and rock increased and ground 

 cover by vegetation decreased on the grazed water- 

 sheds. Runoff averaged 30 percent less from un- 

 grazed than from grazed watersheds, and sedi- 

 ment yield was 45 percent less. He concluded 

 that, within a physiographic area, runoff is di- 

 rectly related to the percentage bare soil. 



Litter Accumulation 



The effect of grazing on residue and litter 

 accumulation is important to the moisture re- 

 gime. Decrease in litter accumulation as grazing 

 intensity increases has been reported by sev- 



eral workers. Reed and Peterson (43) found 2 to 

 2.5 times as much litter following light grazing 

 when compared with heavy grazing. Air dry 

 weights of from 47 to 54 gm./m. 2 of interspace 

 under heavy grazing contrasted with 83 to 142 

 gm./m. 2 under light grazing. Organic matter con- 

 tent of the surface 5 cm. of soil ranged from 1.64 

 to 2.61 percent under heavy grazing, and from 

 1.67 to 2.74 percent under light grazing. 



Chandler (8) concluded that grazing was an 

 undesirable practice in wooded areas of eastern 

 United States because it reduced organic matter 

 content of the surface soil through reduction in 

 litter accumulation. The reduced organic matter 

 content and the trampling by livestock reduced 

 porosity of the surface soil, which resulted in 

 reduced water-holding capacity. However, isola- 

 tion from grazing, or light grazing, may also be 

 detrimental to the vegetation (35, 54)- Accumu- 

 lation of excessive mulch was found to retard 

 growth and hinder seedling establishment. Re- 

 duction in number of species present and reduced 

 growth and flowering were also reported. 



One of the most comprehensive reports on the 

 effects of mulch on grassland environment was 

 published by Hopkins (26). He studied the 

 mixed prairie near Hays, Kans., to determine 

 the amount of mulch, its rate of decomposition. 

 and its effect on infiltration, soil temperature, 

 evaporation and soil moisture. He found that 

 under favorable moisture conditions. 3 to 4 yean 

 were required for the decomposition of vegetative 

 material on the soil surface. By the second year 

 from 40 to 60 percent of the initial weight hac 

 been lost, and the leaves of all grasses had dis 

 integrated, leaving only a fibrous material. B} 

 the third year, the lower layer of mulch wa: 

 intermixed with mineral soil. 



Microbial activity in the mulch layer and th 

 surface layers of soil are influenced by change 

 in microenvironment. The rate of decompositioi 

 of the litter is therefore also affected. Witkam] 

 (55) studied microbial activity in oak. pine, am 

 maple stands near Oakridge. Tenn. He follower 

 bacterial and fungal counts, mycelial growtl 

 microbial evolution of C0 2 . and moisture an 

 temperature changes in the litter at biweekl 

 periods for one year. He found that microbi; 

 respiration was controlled in decreasing order b 

 temperature, bacterial density, moisture and tin 



