CHAPTER V 

 THE PLANT FOOD SUPPLY 



In order that maximum crops of vegetables may be produced 

 it is essential that the soil be abundantly supplied with plant 

 food in a readily available form. Much heavier applications of 

 fertilizing materials are needed for the production of vegetables 

 than for the growing of the ordinary farm crops. Since, in many 

 vegetables, the quality as well as the quantity of the product is 

 profoundly influenced by the amount of plant food available, it 

 is especially important that the supply be ample. 



Elements of Plant Food. — Although it is generally recognized 

 that there are at least ten elements of plant food essential to the 

 development of any crop, all but three can usually be secured by 

 the plant from the soil, air, and water in sufficient amounts for 

 the production of maximum crops. These three elements (which 

 are present in all soils, but often in insuflficient quantities in an 

 available form) are nitrogen, phosphorus and potassium. If one 

 or more of these elements is deficient the productive capacity of 

 the land is thereby diminished. The aim of the vegetable grower 

 in fertilizing land is to supply these elements in the right propor- 

 tions for the development of maximum crops of the vegetables 

 in question. Different soils and different crops need these ele- 

 ments in different proportions. 



Sources of Plant Food. — Plant food for the growing of vege- 

 table crops may be secured from a number of different sources. 

 Only a small part of the plant food present in an untreated soil 

 is available to the plants at any given time. Judicious tillage and 

 the incorporation of organic matter in the soil will render available 

 part of the plant food that would otherwise remain in an insoluble 

 form and hence of no immediate use to the plants. 



However, in vegetable gardening, tillage alone is usually in- 

 adequate to render sufficient plant food available to the plants 

 for the production of profitable crops. Therefore, direct applica- 

 tions of plant food must be made. The chief sources of plant 

 food that can be employed in vegetable growing are animal ma- 

 nures, green manures and commercial fertilizers. 



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