SOILS AND FERTILIZERS 



Nitrogen is invariably needed on hard-run lands, but it costs 

 more, if purchased in fertilizers in quantity sufficient to meet the 

 demands of the soils for full crop production, than phosphorus and 

 potassium combined. 



When fertilizers are applied to the soil, even though they con- 

 tain much water-soluble plant-food, there is but little danger 

 of loss by leaching from the soil. Soil with but few exceptions con- 

 tain those elements which are necessary for the fixation of plant- 

 food. Exceedingly sandy soils do not have the power of fixing or 

 making insoluble the plant-food which is applied in fertilizers. Most 

 soils, however, contain enough of those materials such as lime, iron, 

 aluminum, zeolites and organic matter, which combine with the 

 soluble plant-food applied in fertilizers and make it insoluble so that 

 it does not leach from the soil. Even though it is rendered insoluble 

 in water and hence leaches from the soil only in very small quanti- 

 ties, it is still available to the feeding rootlets of the growing crop. 



Generally speaking, all forms of phosphoric acid and potash 

 are fixed in the soil; nitrogen (with the exception of nitrates), which 

 is contained in stable manure and other organic substances, and 

 also nitrogen in the form of ammonia compounds is fixed in the 

 soil. 



The fixation of the potash and ammonia compounds is brought 

 about by the so-called zeolites in the soil. The phosphoric acid com- 

 pounds are fixed in the soil by compounds of lime, iron, aluminum 

 and possibly magnesium. The exceptions to the above are, 1st, that 

 all forms of soluble plant-food tend to leach out of very sandy 

 soils. 2d, that nitrogen in the form of nitrate tends to leach out of 

 all kinds of soils. 



Soils differ in their requirements for plant food. Some respond 

 to applications of phosphoric acid, others to nitrogen and others to 

 potash. Sometimes a soil requires two or more kinds of plant food. 

 The reason that soils differ in their requirements for plant food are 

 as follows: 



First. Soils are naturally different in their chemical compo- 

 sition, and their needs for plant food. As a rule, sandy soils are 

 more likely to need potash than clay soils. They are also more likely 

 to require nitrogen. The material of which clay soil is composed 

 naturally contains more potash than the materials of sandy soils. 



Second. Soils originally the same may become different 

 through different treatment. One kind of crop may exhaust the soil 

 of one kind of plant food and at the same time there is an abund- 

 ance of the others. The cultivation of different crops in succession 

 instead of the continuous culture of the same crop on the same soil, 

 year after year, is more likely to utilize completely the plant food 

 in the soil. 



WHY DIFFERENT CROPS NEED DIFFERENT FERTILIZERS. 



Crops differ in their requirements for plant food. Some require 

 considerably more potash or nitrogen or phosphoric acid than others. 

 They also differ in the ability which they possess to secure plant food. 

 Some plants grow quickly and must take up their plant food rapidly. 



