144 THE USE OF COMMERCIAL FERTILIZERS 



class of fertilizers with the annual crops, and there are good 

 reasons for such practice as shown by fertilizer experiments. 



Annual crops, whether oats, corn, potatoes or vegetables, 

 require that their food elements shall be ready to hand as their 

 growth makes new demands. The commercial fertilizer, then, 

 should be able to furnish available food elements throughout 

 the growing season, and in the proper proportion required by 

 the crop. 



A study of the chemistry of plant growth shows very clearly 

 that there must be present a continuous supply of available 

 nitrogen, which requires that some shall be in the inorganic 

 and some in organic form. 



The more quickly the crop is to be grow^n in the spring, the 

 more inorganic nitrogen will be needed, since it is sooner 

 ready for the plants than organic forms. Soluble phosphoric 

 acid produces results more quickly and thoroughl}^ than the 

 other forms, and a well-made fertilizer should have at least 

 half of its available phosphoric acid in the soluble form. All 

 crops remove from the soil much more potash than phosphoric 

 acid, and although the soil may furnish some of it, without 

 the positive evidence of field experiments to that effect, a fer- 

 tilizer should have at least as much potash as it has soluble 

 phosphoric acid. 



Commercial fertilizers may be advantageously used in top- 

 dressing grass, and for such a purpose it should have a high 

 percentage of nitrogen, of which nearly all should be inorganic. 

 The phosphoric acid should be nearly all soluble in order to be 

 of marked benefit, and the fertilizer should be applied in early 

 spring while the soil is thoroughly moist. 



Finally, in the purchase of fertilizers it should be borne in 

 mind that it costs just as much to mix, bag, freight and handle 

 a ton of low grade fertilizer as one of high grade. By pur- 

 chasing a half ton of the highest grade goods one buys more 

 and better nitrogen, as much potash and enough phosphoric 

 acid to balance them, for less money than he would pay for a 

 ton of low grade goods, because he saves half the cost of the 

 above different items. 



