CROP ADAPTATION 497 



matter, which will hold the soil together and increase 

 its moisture content, which latter also greatly aids the 

 process. (4) In fine-textured soil, such as silt and very 

 fine sand, by the promotion of granulation and by the 

 avoidance of a loose fallow surface at that season of 

 the year when wind erosion is likely to be serious. 



The aggregate of soil moved from tilled fields by 

 erosion of these two types is large, and it usually con- 

 cerns the most productive portion. The encroachment 

 of sand-dunes upon valuable land is often a serious 

 menace. Reforestation and the planting of sand-binding 

 grasses are the chief protective measures available. 



IV. ADAPTATION OF CROPS TO SOIL 



It is a matter of common observation that all crops 

 do not grow equally well upon the same soil. 



352. Philosophy of crop-adaptation. Each plant is 

 adapted to make its best growth on a particular soil 

 and under a particular climate. Any departure from 

 these ideal conditions results in changing the character 

 of the plant and reduction in its value. This peculiar 

 adaptation of crop to soil is the result of centuries of 

 natural selection. The basis of all the tillage operations 

 which have for their object the modification of the soil 

 conditions is to bring the soil more nearly to the ideal 

 condition required to nourish plants. This wide differ- 

 ence in the preferences of crops is well known. On the 

 other hand, there are hundreds of different kinds of 

 soil, that is, soils which normally maintain different 

 conditions for growth. Some are fine, others are coarse; 



FF 



