COMMERCIAL FERTILISERS 389 



The second, "In what form can I buy each plant 

 food cheapest?" 



What and how much fertiliser to apply as a 

 fertiliser depends upon the deficiency of the soil, 

 the needs of the crop, the system of farming, and 

 kindred matters. 



Soil Analyses as a Guide to Fertilising. If the 

 crops are unsatisfactory, and this cannot be 

 wholly explained by a poor texture of the soil, 

 a deficiency of available plant food may be sus- 

 pected. But what kind of plant food, and how 

 much fertiliser will it pa^ to apply ? The first thing 

 that many farmers do is to send a sample of the 

 soil to a chemist to be analysed; for, they argue, 

 if crops grow on plant food in the soil, surely an 

 analysis of the soil should show just what it needs. 

 But the chemical analysis of a soil rarely gives 

 reliable information about the best way to fertilise 

 it. The analysis of a certain soil may show that 

 there are 5,000 pounds of phosphoric acid in the 

 upper nine inches, but it does not and cannot show 

 how much of this vast amount is soluble, or in 

 such a form that plants can use it; this makes 

 a great deal of difference, from the farmer's 

 point of view. An analysis often points out 

 glaring deficiencies and gives hints that may 

 be valuable in fertilising a soil; but it is 

 by no means a reliable guide, and it usually 

 bears no relation to the method of fertilising 

 which will be found most profitable on that 

 soil. 



It is generally understood, however, that cer- 

 tain types of soils have special needs. Clay and 

 other heavy soils are usually rich in potash, but 

 poor in phosphoric acid; sandy soils, and all others 

 deficient in humus, lack nitrogen; peat and muck 



