GRAZING EANGES IN SOUTHERN ARIZONA. 



25 



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 increasing 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 esti- 

 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 iDeights of hay cut on separate plats in successive 

 years on the Santa Rita Range Reserve, Ariz. 





Plat A, near middle fence, 

 1 acre. 



Plat B, near Proctor's 

 hay camp, 1.4 acres. 



Plat C, near old hay- 

 stack, 1 acre. 



Number of cutting. 



Year. 



Yield 

 per 

 acre. 



Yearly 



de- 

 crease 



in 

 produc- 

 tion. 



Year. 



Yield 

 per 

 acre. 



Yearly 



de- 

 crease 



in 

 produc- 

 tion. 



Year. 



Yield 

 per 

 acre. 



Yearly 



de- 

 crease 



in 

 produc- 

 tion. 





1910 

 1911 

 1912 

 1913 

 1914 



Lhs. 



1,036 

 769 

 463 

 241 



Per ct. 



'""25.'s' 

 39.8 

 47.7 



1911 

 1912 

 1913 

 1914 



Lbs. 



1,037 

 692 

 496 

 376 



Per ct. 



"33.3" 



28.3 

 24.2 



1910 

 1911 

 1912 

 1913 

 1914 



Lbs. 



0) 

 521 

 441 

 322 

 309 



Per ct. 



Second time . 





Third time 



15.3 



Foxirth time 



26.9 



Fifth time 



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 decease 

 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 



