198 INTRODUCTION TO GENERAL SCIENCE 



business. It may be that the land is well stocked with all 

 the material necessary to produce a healthy growth of all 

 kinds of crops, and so the farmer may go on, year after year, 

 without taking any care of his land. Sooner or later, however, 

 the time will come when all the valuable plant food has been 

 removed from the land, and it becomes worthless. This is 

 the cause of many an abandoned farm. If, however, the 

 farmer returns to the soil those elements and combinations 

 of elements which have been removed by the particular 

 crop which he has just harvested, the land will remain in a 

 proper condition. Nowadays the farmer can have access to 

 books in which are given tables that show just what kind 

 of plant food is necessary for each kind of crop, and just how 

 much of each material is taken away for every ton of harvested 

 crop. He may then know just how much material he must 

 return to the soil. Thus some crops, e.g. wheat, require a 

 large amount of phosphorus, and that plant food must be 

 returned to the soil, or it will be impossible to raise another 

 crop of wheat, unless, as has been mentioned, there is a large 

 store of phosphorus in the land. It must be remembered, 

 however, that it is poor economy to exhaust the natural 

 fertilizer of the soil, for the commercial fertilizer; that is, 

 any fertilizer made by man is not as readily assimilated by 

 the plants as the natural plant food* There are three gen- 

 eral kinds of plant food: nitrogen, phosphoric acid, and 

 potash. 



References : 



1. 1601 : 3. The Business of Farming. 



2. 1605 : 380-383. Farm Records and Accounts. 



a. 1604 : 4. The Meaning of the Word Farm. 



b. 1606:11. Agriculture and Business. 



c. 1713:150. Field Trials. 



