350 MANURE AND COMMERCIAL FERTILIZERS 



acre each year, while the truck growers generally apply 

 15 to 25 tons annually. If a commercial fertilizer is used 

 to supplement stable manure, this amount may be con- 

 siderably reduced. 



Commercial Fertilizers. It is seldom that fertilizing 

 with commercial fertilizers cannot be practiced profitably 

 by the vegetable grower. This is particularly true when 



an adequate supply 

 of animal manure 

 is not available. 

 Manures are richer 

 in nitrogen than in 

 phosphorus and po- 

 tassium, and hence 

 even where large 

 quantities of stable 

 manure are used, in- 

 creased production 

 usually results from 

 the addition of these 

 two elements of plant 

 food. Some forms 

 of commercial fertili- 

 zers, too, are more 

 quickly available 

 than manure and hence earlier crops may be produced 

 by their use. Vegetables of a higher quality are also 

 possible, as slow growth is likely to produce bitter, tough, 

 and stringy vegetables. 



Nitrogen. Nitrogen is the most important element of 

 plant food to be supplied on the light sandy soils. In the 

 growth of lettuce, spinach, celery, and other foliage crops. 



Fig. 186. A heavy crop of onions. Grown on muck 

 land to which commercial fertilizers were added. 



