80 BULLETIN 1031, U. S. DEPARTMENT OF AGRICULTURE. 
industry in the Southwest at present, and one of the biggest problems 
of the industry to-day is to overcome these unfavorable conditions. 
Rainfall records over a long period of years and experience of stock- 
men during the past two or three decades indicate that droughts of 
3 to 4 years’ duration may occur in each cycle of 8 to 10 years. 
A study made in southern New Mexico showed that on grama- 
grass range drought alone if prolonged beycnd the second year killed 
40 per cent of the best grazing plants and reduced the quantity of for- 
age produced approximately 50 per cent. Grazing tends to increase 
the effect of drought to a degree varying with the time and amount 
of use, but when limited during the main growing season—July, 
August, and September—to from 30 to 50 per cent of the proper 
yearly rate, it has no harmful effect. The reduction in grazing at 
that time does not interfere with full use of the range, since the 
grass cures and is valuable for winter range. To restore damaged 
grama-grass range to its former condition of productivity will prob- 
ably require several years of judicious handling. 
In the case of tobosa grass or similar range there is less dying out 
of the forage but the amount of feed produced varies more directly 
with the amount of rainfall, so that the reduction in time of drought 
is about the same as for grama grass. Tobosa grass is not easily 
injured by grazing during the growing season and is of little value 
for grazing after it dries up, so that it is well adapted to summer 
grazing. 
Drought has a direct influence upon the carrying capacity of the 
range. Data obtained thus far indicate that range with a grazing 
capacity of 27 acres per cow per year will only carry stock at the 
rate of 32 acres per head the first year of drought, 45 acres the sec- 
ond, 54 acres the third, and 54 the fourth. 
Cattle raising, to be successful under such conditions, must be 
adjusted so that the number of animals will conform to the carrying 
capacity of the range in time of drought. In other words, there 
should be a reduction to 85 per cent of the original number the first 
year, to 60 per cent the second, and to 50 per cent the third. 
Since the Southwest is primarily a breeding section, and it is dif_f- 
cult to dispose of breeding cows upon short notice, the breeding herd 
should be confined to what the range will carry in poor years or to 
50 per cent of the carrying capacity during good years. The surplus 
forage in good years may be utilized profitably by holding over or 
buying young steers or heifers to be disposed of in time of drought 
to make all range available for the breeding cows. The age, number, 
and class of such stock to carry will depend upon the forage not 
needed for the breeding cows and the market. 
Division of grama-grass and tobosa-grass types of range, when the 
two occur together on a range unit, and using the former in winter 
