removal of crops in soil depletion, especially when these crops are 

 removed by grazing animals. The problem rightly considered is there- 

 fore mainly a matter of soil erosion. But it must not be forgotten 

 that even where there is no erosion, cultivation itself tends to destroy 

 the organic matter; and consequently all cultivated crops stand at the 

 top of the list of soil robbers. 



On the other hand, crops that can be grown with a minimum of 

 stirring the soil are in varying degrees soil-conserving crops . As pointed 



out, the minerals in the soil cannot be wholly conserved 

 Soil-Con- if the crop is to be utilized ; but the loss of minerals, 

 serving Crops except from erosion, is not heavy, and minerals can be 



economically replaced. Noncultivated crops, such 

 as alfalfa, clover, lespedeza, Kudzu, grass hay, and pasture, conserve 

 the organic matter in the soil, and that is the important thing (fig. 2, 

 A and B). The growing of these crops, therefore, tends to con- 

 serve the soil even if some minerals are carried away in the crop. 



These close-growing crops prevent erosion with its attendant loss 

 of organic matter and minerals. The annual stirring of the soil 

 necessary to the culture of a small-grain crop occasions some loss of 

 organic matter and allows more erosion than is permitted by a meadow 

 or pasture (fig. 2, (J). A small-grain crop can be called a soil-con- 

 serving crop, therefore, only by comparison with a crop that is more 

 soil depleting, such as corn or cotton. In comparison with a meadow, 

 small grain is a soil-depleting crop. Again it may be pointed out that 

 the term "soil-conserving crop" is a relative one. Crops conserve the 

 soil to the degree to which their culture is possible with a minimum of 

 soil stirring and in proportion to the density and permanency of cover 

 they provide. The removal of plant food by the plant, which is a 

 necessary accompaniment of utilization, plays a minor part in soil 

 depletion. The concept of soil conservation covers the maintenance 

 of soil productivity, and those crops that best serve to maintain the 

 productivity of a soil while being utilized are the best soil-conserving 

 crops. 



Soil-building crops must go further; they must not only conserve 

 what is there but must build it up, make the soil better. Here again 



it is the organic matter that counts. Plants cannot 

 Soil-build- build up the minerals; all they have came from the 

 ing Crops soil; if the plants are turned under, just so much 



goes back to the soil. If the soil needs more lime, 

 phosphorus, or potash it must be added. 



Plants can, however, build up the organic matter and with it the 

 nitrogen content of the soil. Legumes, of course, work best as nitro- 

 gen gatherers. They get a large part of their nitrogen from the air, 

 and if they are turned under, the soil will have that much more nitro- 

 gen. In this connection, the kind of legume used and the way it is used 

 must be considered. Soybeans cultivated in rows and harvested as 

 hay. are about as competent soil robbers as corn. They permit 

 erosion and the destruction of organic matter. Even when the soy- 

 beans have been well inoculated there is more nitrogen in the soybean 

 hay than the plant took from the air, and since the root system is 

 relatively small, little nitrogen is returned to the soil. This statement 

 applies equally well to other annual legumes, such as cowpeas and 

 velvetbeans, if they are removed from the ground. When these 

 crops are broadcast or planted in close drills they help somewhat to 



