APPLIED ECOLOGY 339 



ress has been made in educating the public to the need for a con- 

 tinuous program of conservation, and soil conservation as a science 

 has developed rapidly. The scope of the field and the problems 

 involved have been admirably summarized in various publica- 

 tions. 18 ' 136 



Early publicity by soil conservationists was essentially a plea to 

 save our irreplaceable land, a great deal of which was already per- 

 manently lost and much of which is in the process of being ruined. 

 More recently, the emphasis has been upon rebuilding lands that 

 have deteriorated. The modern philosophy considers soils, like 

 forests, to be natural resources that are renewable and, therefore, 

 subject to management that will give a sustained yield over an 

 indefinite period of time. 174 Such a program is, of course, as justifi- 

 able as the original, which aimed primarily at erosion control. It 

 indicates that the conservation program has been successful and is 

 maturing. 



Soil conservation is, therefore, more than erosion control. It 

 also involves the retention of water, especially on slopes, and its 

 utilization to best advantage. At the same time, it aims to maintain 

 or increase soil fertility and productivity. Thus soil conservation 

 is merely the practice of agriculture in the best possible way, and 

 we have already suggested how the ecological approach to such 

 problems is most likely to be successful. 



Not all the various measures successfully introduced for erosion 

 control and soil building are applicable everywhere but must be 

 adjusted in terms of soil types and climate. However, certain gen- 

 eralizations can be made which have wide application and whose 

 special use or desirability often must be determined by a knowl- 

 edge of local ecology. Vegetative- cover is the most effective means 

 of checking erosion. This raises questions as to what cover is de- 

 sirable or possible under different conditions, where it should be 

 permanent, and when it should be of native vegetation. These 

 problems are related to strip-cropping, gully control, cover crops, 

 and decisions to cultivate hilly land, put it into pasture, or plant it 

 to forest. It is now assumed that the control of erosion will pay 

 dividends only when proper crop rotations and fertilizing prac- 

 tices are followed. The interrelationships must be known for every 

 crop and region. 



