376 SOILS 



of applying it to the land is greater, since more 

 has to be applied to give a certain result. Usually 

 plant food can be bought more cheaply in a con- 

 centrated, or "high-grade fertiliser" than in a low 

 grade. Even though a low-grade fertiliser may 

 contain some high-grade materials, as sulphate 

 of potash and nitrate of soda, the plant food in it 

 usually costs more because this is weighed down 

 with so much useless bulk. The farmer cannot 

 afford to pay for bulk. Every pound of material 

 in a ton of fertiliser which is not plant food 

 adds to the price which the farmer must pay for 

 the plant food. Usually the more concentrated 

 the fertiliser, and hence the higher the price per 

 ton, the cheaper it is. But one cannot make a 

 mistake in buying a low-grade fertiliser if he figures 

 on the guarantee. 



ADVANTAGES OF HOME-MIXING OF FERTILISERS 



It is a convenience to buy fertilisers mixed and 

 ready to apply, provided the buyer examines the 

 guarantee and finds that he can buy plant food in 

 this fertiliser about as cheaply as though he bought 

 the raw materials and mixed them himself; and 

 provided, too, that this brand of fertiliser contains 

 the several kinds of plant food in the right pro- 

 portions for the soil and the crop to be grown. 

 J3ut this is not usually the case. Few farm soils 

 need applications of all three plant foods; many 

 need but one. Many brands of commercial fer- 

 tilisers contain all three and the farmer may be 

 buying plant food that his soil does not need, and 

 so wasting his money. 



The raw materials out of which commercial fer- 

 tilisers are made, may be bought and mixed on the 



