MARYLAND GEOLOGICAL SCKVEY 141 



and confined to the few who have ventured their money and their time, 

 has led to the partial classification already noted. It is hoped that the 

 classification, the inap, and the description of soil types contained in 

 this report will facilitate further development along the lines of soil 

 selection for special crops, will encourage the introduction of new crops, 

 and will lead to a generalization of the experience gained hy the few 

 for the use of the many. 



Closely associated with the adaptability of certain soil types to certain 

 crops is the two-edged cpiestion of fertilizer, which is dependent for 

 its answer upon the quality of soil to be fertilized and the kind of crop 

 to be raised. 



Probably every soil type in .St. Mary's County contains within 4 feet 

 of its surface sufficient plant food to produce 100 crops of any kind 

 which are raised or could be raised in the county. The necessity for 

 fertilizer depends on the fact that much of this material is present in 

 such chemical combinations and in such a physical state that some 

 manipulation is required to release it and to bring it into solution in 

 water so that the plant roots may absorb it. Certain chemicals found 

 in commercial fertilizers and in stable manures tend to release this 

 plant food and to form or supply soluble chemical compounds suited 

 to the needs of the plants, while organic matter constitutes the best sponge 

 for retaining the absolutely essential water supply in sandy soils, and 

 acts equally well in loosening the too closely packed particles of heavier 

 clay soils. The organic matter, through its decay, also furnishes actual 

 plant foods and solvents for the preparation of other foods. The 

 character of growth desired in special crops modifies the kind and amount 

 of special fertilizers for those crops. For example, it is a generally 

 accepted principle of tobacco culture in Maryland that liming land spoils 

 the texture of the tobacco raised, causing it to spot and injuring the 

 burning qualities for wdiich it is so well known ; therefore the use of lime 

 on tobacco lands is precluded, though its use would be of undoubted 

 advantage on all of the heavier soil types and upon most of the lighter 

 types for other crops. 



St. Mary's County possesses large stores of carljonate of lime in the 



