374 SOILS 



buying a fertiliser the farmer should consider just 

 two things; the amount of plant food in it and 

 what it costs per pound in this form. It is a 

 simple matter to estimate the value of a com- 

 mercial fertiliser from its guarantee, provided the 

 guarantee is not too confusing. Suppose a fer- 

 tiliser is offered with the following guarantee: 



Per cent. 



1. Ammonia 2 to 4 



2. Available phosphoric acid 10 to 12 



3. Total phosphoric acid 14 to 17 



4. Equivalent to bone phosphate . . . . 30 to 37 



5. Potash 9 to 11 



6. Equivalent to sulphate of potash . . . 16 to 20 



The first thing to do is to draw a line through 

 statements 4 and 6, because 4 is a repetition of 

 2 and 3, while 6 is a restatement of 5. The 

 ammonia must now be reduced to nitrogen by multi- 

 plying 2 per cent, by .82, giving 1.64, the percent- 

 age of actual nitrogen in the fertiliser. Since 

 there is 14 per cent, of phosphoric acid in the fer- 

 tiliser and but 10 per cent, of this is available, the 

 inference is that the other 4 per cent, is insoluble. 

 A simplified statement of the contents of this 

 fertiliser is: 



Per cent. 



Nitrogen 1.64 



Available phosphoric acid 10 



Insoluble phosphoric acid 4 



Potash 9 



The number of pounds of each plant food in a ton 

 of this fertiliser is then determined: 



1.64% of 2,000 lbs.= 32.8 Ibs. of nitrogen in a ton. 

 10% of 2,000 lbs.=200 Ibs. of available phosphoric 



acid in a ton. 



4% of 2,000 lbs.= 80 Ibs. of insoluble acid in a ton. 

 9% of 2,000 Ibs.=rl80 Ibs. of potash in a ton. 



