34 THE FUTURE OF ARID LANDS 
100 years. Rather elaborate techniques and apparatus are needed 
and several factors affect the interpretation of the results; yet the 
method holds promise for studying the fate of the rainfall in criti- 
cal areas and for calculating the contribution of recent rainfall to 
ground water, streams, and plant growth. 
Despite some fair progress, we need more detailed data on 
supplies of ground water, rates of recharge, and conditions aftect- 
ing recharge. That is, we need more application to specific areas 
of current methods for hydrological definition. 
Still adequate use is not being made in many places of the data 
already in hand. It has been definitely shown that ground water 
is being used in some areas far faster than the recharge. This has 
been explained to the people in these areas. In some areas the 
people have developed local voluntary associations or legal 
schemes to protect the water supplies. Good progress has been 
reported from North Africa for example, where herdsmen have 
worked out ways to protect their water supplies for livestock 
and for feed reserves against the dry years. 
In other areas, legal and administrative devices to deal with the 
problem are lacking. In these, social research and invention are 
lagging behind physical research and invention. 
Soil 
Ibn-al-Awan, the Moorish agriculturist of the twelfth century, 
began his great book on agriculture with the sentence: ‘The 
first principle of agriculture is an understanding of soils and of 
how to distinguish those of good quality from those of poor 
quality.”’ But despite such admonitions, many people have wasted 
their lives trying to irrigate unresponsive soils. 
It was not until about the end of the nineteenth century that 
examinations of soil were made as a part of a more or less routine 
evaluation of their potential use and capabilities. At first, texture, 
slope, salt content, and wetness or depth to the water table were 
the features considered. Even such limited studies were largely 
confined to the young alluvial valleys where it was convenient to 
use irrigation water. It is only in the last few years that studies 
have been made of the old and stable upland soils of the desert 
