RESEARCH AND DEVELOPMENT 59 
3. Development of structure and water-holding capacity in arid 
sandy soils through use of better adapted green-manuring crops, organic 
soil conditioners, or in other ways. 
4. Better methods are needed for appraising the salt balance in whole 
watersheds where irrigation water is taken from streams and the drain- 
age water is returned into the streams to be used again for irrigation at 
one or more lower levels. 
5. More precise studies are needed of the soil properties that lead to 
chlorosis in plants and of ways to modify them. 
6. The reasonable alternative combinations of plant nutrients, water 
supply, plant spacing, and cropping systems need to be tested in order 
to find the most nearly optimum ones for each kind of soil in terms of 
harvest, sets of practices, and the long-time effects on soil productivity. 
Vine agulkss moe be eee onan ta de specific terms required for calculat- 
ing costs and input-output ratios needed in farm budgeting. 
Plants 
In the section on climate reference was made to the fact that 
there is little evidence of any marked climatic change for the 
worse since man used or misused the land for living. The effective- 
ness of the rainfall has however been seriously reduced by man’s 
overuse of plough, the axe, and the grazing animal, particularly 
the goat. Marginal areas have become man-made desert areas, 
and it is in this sense that the desert is advancing. In any attempt 
to re-establish marginal areas for better production and living 
conditions it is necessary to survey and map the existing plant 
cover, whether natural or cultivated, and also land use. These 
are being done or are planned by FAO working with national 
authorities. 
The main task is to attempt the regeneration of a better plant 
cover and to do this while the population is engaged in gaining a 
living from the area. To study such natural regeneration as may 
occur it 1s essential to have as guides in this work enclosed or 
protected areas which are ungrazed. Sometimes the results may 
be startling. One thing cannot be done, and that is go over from 
one area in one part of the world to another area in another part 
and at once begin to apply procedures in the expectation that they 
will be successful. Much experimentation is needed to select suit- 
able plants, to get them to seed, to germinate, and to grow in 
these very old environments. 
