90 



high quality of produce are important factors. The areas now neces- 

 sarily devoted to these crops are so great that the amount of farm ma- 

 nures available is much too small ; besides, the constituents contained 

 in such manures, being slowly available, are less useful than the more 

 active forms contained in commercial fertilizing materials. They are 

 in a sense artificial crops and, as a rule, need artificial supplies of plant 

 food. 



Fruit culture, an industry of growing importance, is profitable, par- 

 ticularly on the poorer soils near the Eastern markets, largely in pro- 

 portion to the supply of the mineral elements in excess of those contained 

 in soils otherwise well adapted to the crops. A sufficiency of food not 

 only enables the trees to resist unfavourable conditions, but improves 

 the quality of the fruit and extends the bearing period of the orchards 

 and vineyards. 



It will thus be seen that it is either to make up the deficiencies of 

 farm manures or in specialized intensive farming that commercial fer- 

 tilizers can be most advantageously used. The latter should supple- 

 ment and not entirely replace the manurial resources of the farm. They 

 give best results as a rule on soils well stocked with organic matter 

 (humus), a material which can be maintained in soil only by the regular 

 application of the bulky farm manures (including green manures). 



FERTILIZER REQUIREMENTS OF DIFFERENT SOILS AND CROPS. 



Nitrogen, phosphoric acid, and potash are the constituents most likely 

 to be deficient in soils or most quickly exhausted by the production and 

 removal of crops. These are known as " essential" fertilizing consti- 

 tuents, and the value of a commercial fertilizer is determined almost 

 exclusively by the amount and form of the nitrogen, phosphoric acid, 

 and potash which it contains. It does not follow, however, that all soils 

 or crops will respond equally to applications of materials containing these 

 elements, because the needs of soils and the requirements of crops vary. 



Soils differ in respect to their needs for specific elements, owing either 

 to their method of formation or to their management and cropping. A 

 sandy soil is usually deficient in all the essential plant-food constituents — 

 nitrogen, phosphoric acid, and potash — while a claj^ey soil usually 

 contains the mineral elements in abundance, particularly pot;ish. On 

 the other hand, a soil very rich in vegetable matter is frequently de- 

 ficient in mineral matter, while a limestone soil is likely to contain 

 considerable proportions of phosphoric acid. These are the indications 

 in a general way, and they explain why it is that different kinds of 

 soil that have not been cropped differ in respect to their needs in re- 

 ference to the different fertilizing constituents. 



Methods of management and cropping also exert an influence ; for 

 example, soils of equal natural fertility may not respond equally to 

 uniform methods of fertilization, because in the one case a single crop, 

 requiring for its growth proportionately more of one of the essential 

 elements than of another, is grown year after year, and it may be that 

 the element required is the one that exists in the soil in least quantity. 

 On the other band, crops may be grown that demand but minimum 

 amounts of the element in question; hence its application to the soil 

 for the one crop may be followed by largely increased returns, while 

 for the other but little if any increase in crop is apparent. 



