MIXED FERTILIZERS 41 



the guaranteed analysis and the price correspond, and 

 granted that the material is in a good, convenient condition 

 for sowing, and that the mixture really represents what the 

 crop on that particular soil and under that particular climate 

 wants, then this mixture may be used with satisfaction. 

 For the purpose of checking the prices of these materials, 

 a unit of 22*4 pounds is commonly adopted. For Great 

 Britain these unit prices are published in the Journal of 

 the Board of Agriculture, which will give the values from 

 time to time. For example, in the number for April, 1917, 

 one may see that in London the unit price of nitrogen in the 

 form of sulphate of ammonia was 15s. ^\d., but that nitrogen 

 in other forms was more expensive, and that at all the other 

 places named in the table the same was true. Thus with an}' 

 mixture in which nitrogen is probably derived from sulphate 

 of ammonia it would be not unreasonable to take this figure. 

 The value of a unit of soluble phosphate in super-phosphate 

 varies according to place from 3s. i\d., to 4s. S\d., and for 

 rough purposes one may call it 4s. At the time potash is 

 not quoted, but before the war potash was valued at 3s. or 

 4s. a unit. A calculation can be made as follows : — 



Table 5. — Manure. 



£ s. d. 

 Nitrogen, 5 per cent., at 155. .. .. .. .. 3 15 o 



Soluble phosphate, 20 per cent., at 4s. .. .. 4 00 



Potash, 3 per cent., at 105. . . . . . . . . i 10 o 



Mixing, bagging, etc. .. .. .. .. .. 0150 



Total value . . . . 10 00 



If less than 5 tons, add 5 per cent. . . . . . . 0100 



If payment delayed till harvest, add 5 per cent. . . 0106 



£11 o 6 



Prices will vary from time to time, but are published 

 monthly in the Journal of the Board of Agriculture. 



It is not difficult to make one's own estimate of unit 

 prices for one's own special conditions. Sulphate of ammonia 

 contains so nearly 20 jjer cent, of nitrogen that the unit price 

 of nitrogen in sulphate of ammonia is almost exactly the 

 same in shillings as the price is in pounds per ton, that is, 

 when sulphate of ammonia costs about £*i6 per ton the unit 



