498 THE PRINCIPLES OF SOIL MANAGEMENT 



some are deep, others are shallow; some have one chemi- 

 cal composition, others have a different composition; 

 some are dark, others are light-colored; some are wet, 

 others are dry; some occur under one climate, others 



Fig. 154. Lettuce and celery growing on muck soil. Such soil usually requires 



special fertilization. 



under another climate. It is the combination of all 

 these factors which affect plant growth that gives rise 

 to the great variety of soil conditions. The great variety 

 of plants is a reflection of this great variety in the con- 

 ditions of growth. In any given situation, those crops 

 which are adapted to that situation persist and thrive. 



