25 
GRAZING RANGES IN SOUTHERN ARIZONA. 
Using the figures of only those instances in which the actual area 
is known and the total weight is also known gives an average 
of 558 pounds per acre. A comparison of these two figures would 
seem to indicate that probably some of the estimates were too high, 
thus mcreasing the average output of hay per acre for all cuttings. 
But a careful examination of the details of the records shows that it 
has so happened that all the records which show no element of est1- 
mate in them, except four, which are for small areas and therefore 
have little weight in the averages, are obtained from areas that have 
been mowed year after year for three to five years in succession, while 
many of the records which depend in any degree upon some one or 
more estimated factors are obtained from areas of medium to rather 
large size which were being cut for the first time. The hay from 
the latter kind of areas always contains a certain percentage of old 
grass which did not grow during the season that the hay was cut; 
hence, estimates of average production from such areas alone must be 
in excess of the average seasonal production. That estimates made 
from records of comparatively small areas which have been mown 
several years in succession must be somewhat under the average pro- 
duction will be seen by an examination of Table V, in which com- 
parisons are given of the weight of hay cut from the same areas in 
successive years. 
TABLE V.—Comparison of the weights of hay cut on separate plats in successive 
years on the Santa Rita Range Reserve, Ariz. 
1 acre. 
hay camp, 1.4 acres. 
stack, 1 acre. 
a A,near middle fence,| Plat B, near Proctor’s | Plat C, near old hay- 
| 
| 
Number of cutting. Yearly Yearly Yearly 
Yield ee Yield oe Yield ae 
Year. er ae Year. Perper Year pers icc 
acre. | produc- ACEP produc- a produc- 
| tion. tion. tion. 
Lbs. | Per ct. Lbs. \Per ct Lbs Per ct. 
BTS GING) a ee See 1910 F036) 2223.64- 1911 ISURYS |lSoauon se 1910 (Coie. | eericta oe 
Second time ..-.. =. 1911 769 25.8 1912 692 33.3 1911 52 eee 
hid: times... 2s... 1912 463 39.8 1913 496 28.3 1912 441 15.3 
Fourth GHNCE jee ces oe 1913 241 Avimal 1914 376 24.2 1913 322 2659 
Pith GlImMes of s.n. so: J AEM is Lk frat ls ea aT a Na | oe a el eee 1914 309 4.0 
Total decrease in 
productivity...| 4 years. 795 76.7 | 4 years. 661 63.7 | 4 years. 212 40.6 
1 Plat C was cut in 1910 along with the rest of the area, but the weight of hay on this particular acre was 
not obtained separately. 
From Table V it will be seen that continued cutting of the grass, 
year after year in succession, causes a gradual but marked decvease 
of the crop, ranging in quantity from 4 per cent to nearly 50 per 
cent of the previous year’s growth, the average annual decrease 
being about 25 per cent. The average total decrease in production on 
the three plats for a period of four years is 64 per cent of the crop 
