SCIENCE IN MAN’S STRUGGLE ON ARID LANDS Al 
not been generally applied. We have either inadequate soil sur- 
veys, or none at all, for a large part of the arid lands. Many 
important kinds of soil are still very poorly understood, to say 
nothing of their relations to vegetation and climate. 
Lest what I have said so far lead to overoptimism, let us sum- 
marize the soil-use problems under grazing, dry farming, and 
irrigation. 
Grazing 
The productivity of arid range lands varies within wide limits 
from essentially zero to something like 200 pounds of beef per 
acre (or say 30 pounds of mutton and to pounds of wool), de- 
pending upon the local soil conditions and effective rainfall. 
Thus operational units of comparable size in terms of livestock 
production vary enormously in terms of acres. For this reason 
alone the units on poor soil tend to be too small for the individual 
family or village, and this leads to overgrazing. Since soil moisture 
is variable, there is a tendency to overstock in moist years and 
for such overstocking to continue into average or drier-than- 
average years with resulting overgrazing and damage to the 
basic potentialities of the vegetation and, finally, even of the 
soil itself. 
Once serious overgrazing has taken place, the carrying capacity 
falls far below normal and its recovery depends upon a tem- 
porary sharp reduction in stocking together with reseeding, con- 
touring, water spreading, and other measures to control the water 
and keep it in the soil. 
Then, too, the effective use of grazing land usually depends 
upon sure supplies of feed for critical hot, dry, or cold periods. 
This means that grazing land needs to be associated with irri- 
gated land or with arable land in the mountains or in favorable 
spots where hay or feed crops can be grown. Improved techniques 
for wells and for surface water storage lead to more watering 
places and thus spread the livestock evenly over the range. This 
helps to control the use of the range. 
In predominantly grazing areas generous amounts of water 
should be allocated to use as livestock water and to irrigate 
