40 CIRCULAR 870, IT. S. DEPARTMENT OF AGRICULTURE 



That close grazing did reduce the yield from slopes, however, was 

 quite evident. Several comparisons were made of small areas of similar 

 sites across the fence line between pastures 2 and 3 during the years 

 1943-45; they indicated that the yield on slopes was reduced under close 

 grazing and that the greatest reduction was on the most productive 

 sites. Then, too, in 1944 a fenced plot about 66 feet square was placed 

 astraddle of the fence line between pastures 2 and 3. It was situated on 

 a highly productive gentle-slope soil, in the only area of appreciable size 

 where comparisons of similar sites could be made directly across the fence 

 line. Yield was measured on three sample transects in each pasture. 

 The average in pasture 2 was 3,624 pounds per acre; in pasture 3 it was 

 2,254 pounds — a reduction of 38 percent after 8 years of continued close 

 grazing. 



When the experiment ended in 1948, yields were measured for these 

 two pastures as a whole. In pounds per grazable acre, herbage yields 

 were 1,379 for slopes and 2,225 for swales in pasture 2, and 837 for slopes 

 and 1,224 for swales in pasture 3. On slope sites the yield in the closely 

 grazed pasture was 61 percent of that in the lightly grazed pasture, about 

 the same as in 1943 and 1944. The yield of swale sites, however, was only 

 55 percent of that in the lightly grazed pasture, slightly lower than in 

 the other years when yields were measured. 



Moderate-to-close grazing (pasture 1) had a measurable effect on 

 total herbage yield only in the swales. The average yield on swale soil 

 in pasture 1 was 80 percent of that in the lightly grazed pasture 2 (table 

 10). As was the case with pasture 3, the reduction was caused mainly 

 by heavier grazing. Unlike the case with slopes of pasture 3, however, 

 the lower yield on slope soil occurred mainly because pasture 1 had a 

 lower proportion of the more productive site classes. Comparisons of 

 yield on similar sites across the fence line between pastures 1 and 2 did 

 not reveal any consistent differences that could be attributed to grazing 

 treatment. 



Because the effects of different degrees of grazing on total herbage 

 production were different on each site, the combination of site classes 

 within the pasture had to be considered in judging the extent that pro- 

 duction was reduced by close grazing. To do this a "potential yield" 

 for each of three pastures for 1943-45 was computed. First, the acreage 

 of each site class in the pasture was multiplied by the estimated yield 

 per surface acre of this site class (from table 4) to obtain its expected 

 yield. Then the total potential yield for the pasture was obtained by 

 adding the expected yield from each site class. This computed potential 

 yield for pastures 1, 2, and 3, and the measured total yield from sample 

 quadrats in each pasture were: 



Yield 

 Potential Measured 



Pasture and degree of grazing: (pounds) (pounds) 



Pasture 2 (light) 394,276 395,293 



Pasture 1 (moderate to close) 262,755 262,836 



Pasture 3 (close) 187,815 142,264 



For all sites combined, the closely grazed pasture 3 was producing only 

 about three-fourths of its potential herbage production. Each of the 

 other two pastures was yielding near its calculated potential. Although 

 this method of analysis did not show all the differences between pastures, 



