Feetilizers a\d Feeding Stuefs. ;>71 



calculated unit values of any particular constituent of the few ferti- 

 lizers of the same nature differ so very widely that very anomalous 

 results are obtained. As an illustration in the case "of the most 

 common class of simple fertilizers (bone meal), tliere are only seven 

 brands knbwn to the wi'iter to be on the Cape market at the* present 

 day ; the unit value of the citric acid-soluble phosphoric oxide in 

 these varies from Ts. 6d. in the lowest case up to a maximum of 

 10s. 8d., giving an average all through of a little over 9s. 



The unit value of the nitrogen is given separately for the different 

 classes of nitrogenous fertilizers, for the rate of availability of this 

 constituent varies in each and the applicableness of each class is not 

 the same for all types of soils and crops. In the cases of nitrate of 

 soda, sulphate of ammonia, and blood or meat meal the value per unit 

 of tlie nitrogen was calculated direct. The nitrogen in the organic 

 substance of bone is less readily available to plants than that in blood 

 or meat meal, as owing to the tough nature of this gelatinous material 

 it does not decompose so rapidly in the soil ; for this reason the unit 

 value of nitrogen in bone meals has been arbitrarily fixed at about 

 four-fifths the unit value in blood or meat meal. In genuine dissolved 

 bones, however, the organic matter has been partially decomposed 

 and disintegrated by treatment with acid, and the nitrogen is reckoned 

 as being of the same value as in dried blood. Very often such inferior 

 organic materials as horn and hoof waste, hair, leathers, skin and 

 leather waste, wool and silk waste or shoddy, tanning refuse, etc., 

 are ground up for use as fertilizers, but the rate at which the nitrogen 

 becomes available in such substances is very slow. These, however, 

 are often used as a source of nitrogen in mixed fertilizers owing to 

 their cheapness. When the guaranteed analysis of locally manufac- 

 tured mixed fertilizer states that the source of the nitrogen in it is 

 organic, it is fairly safe to assume that it is in the form of bone meal, 

 unless it is specifically stated otherwise, although it must be stated 

 that dried blood or meat meal is often employed in such mixtures. 



The citric acid-soluble phosphoric oxide is assumed to be of the 

 same value in all phosphatic fertilizers (except basic slag) as that 

 calculated for bone meals. The insoluble phosphoric oxide is also 

 arbitrarily assumed to have a unit value equal to half that of the 

 citric acid-soluble phosphoric oxide, but, strictly speaking, the real 

 value is far from being uniform. The insoluble phosphates in some 

 materials become more readily available in the soil than others; also, 

 the finer the material is ground the more readily available the in- 

 soluble phosphate in it becomes, and consequently the more valuable 

 this constituent should be. 



There is very little in the way of potash salts imported into South 

 Africa at the present time, and there is absolutely none for sale 

 separately. The unit values of the potash in the form of sulphate 

 and chloride have been calculated from data supplied by one of the 

 wholesale firms in Natal, and these figures should be taken as only 

 approximate. The potash materials used mostly' for fertilizing 

 purposes at present are wood-ash. Karroo-ash, and kraal-ash. in all 

 of which the potash is in the form of carbonate. One firm in par- 

 ticular states in its price list that all their fertilizers contain more 

 than sufficient sulphate of lime to convert any carbonate of potash 

 present almost entirely into sulphate of potash, prod. icing at the same 

 time carbonate of liiue. It is true that such a chemical reaction takes 



