Phosphates 



when that unit is contained in the smallest bulk. 

 The percentage of phosphoric acid [P0O5] is very 

 variable, ranging from 25 to 40 per cent, or 50 to 

 80 per cent, as tribasic. 



The difference between the value of monocalcic 

 phosphate, superphosphate, and tricalcic phosphate 

 of mineral phosphates, or of bones, is very great, 

 being proportionate to their solubility and their 

 assimilability. 



In many soils, even when tricalcic phosphate 

 is used in the form of a fine powder it is nearly 

 inassimilable, and will be found of little value. 

 This would be the case in soils poor in humus, also 

 in calcareous soils, even although these contained 

 only a small proportion of lime or magnesia. 



It is not suitable for such soils, and should be 

 used rather as an improvement than as a manure, 

 at a proportionate price of a quarter, a fifth, or 

 even less than that of super. 



Superphosphate is a manure of immediate action 

 and can be applied simultaneously with sowing. 

 Sometimes it is used as a top dressing, although it is 

 preferable to harrow it in. It will give good results 

 with nearly all crops ; but it is most effective on 

 turnips, because they find it more difficult than 

 any other plants to absorb the phosphoric acid of 

 the soil, and so require a very assimilable form of it. 



Since, however, super is somewhat acid itself, 

 basic slag should be used in preference for pastures 

 on very humiferous acid soil poor in lime. It should 

 not be applied to very acid land, because, being 

 soluble and finding no arresting base, it would 

 simply be washed into the drainage and wasted. 



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