484 THE HOME, FARM AND BUSINESS CYCLOPEDIA. 



GROUND OR MINERAL PHOSPHATE Its value as a fertilizer is derived 

 from the phosphate of lime of which the mineral is partly composed. 

 Coprolites, as to seventy to eighty per cent, of their substance, are a mixed 

 phosphate and carbonate of lime. 



Athough there seems to be considerable difference in the results obtained 

 by different experiments, the general conclusion seems to be that the 

 usual difference in the effects produced by soluble and insoluble phosphates 

 is much diminished when the latter are reduced to very fine powder and 

 applied in very large quantities. The powdered phosphate is cheaper 

 than the manufactured manure. But there can be no doubt that an in- 

 creased use of ground coprolites would result in increasing their cost 

 in the market, and the advantage would thus to some extent be lost. 



After fine grinding, the coprolite powder may be mixed with farm-yard 

 manure, either under the cattle or else in the dung heap, and the carbonic 

 acid formed by the fermentation of the dung tends to the solubility of the 

 mineral phosphates by actual superphosphating. 



The addition of superphosphate to a field acts powerfully upon turnips, 

 and other root crops. Its effects are not very evident upon wheat, but 

 it has been noticed to exert a favourable action upon barley, especially 

 when late sown. From what we know of the requirements of plants, we 

 might naturally think that turnips and barley must require a large amount 

 of phosphates, and that wheat had not similar need. This conclusion 

 would be erroneous. For although a root crop certainly does remove more 

 phosphates from a soil than a crop of wheat, a barley crop, practically 

 speaking, requires about the same amount. A fair crop of wheat, of 32- 

 bushels, removes in grain and straw about 26 Ibs. of phosphorus pentoxide 

 from the soil. Twenty tons of turnips, with their tops, take about 40 Ibs., 

 so that a crop of turnips needs 14 Ibs. more than a crop of wheat. Wheat 

 hen undoubtedly requires a less weight per acre, it is proportionately 

 richer than turnips in this element. Why then should phosphates act 

 strongly upon turnips and barley, and scarcely at all upon wheat ? The 

 main reason appears to be the long period during which wheat occu- 

 pies the ground, and the amount of space covered by its roots. A manure 

 is never useful unless it is wanted, and there is usually enough phosphorus 

 pentoxide in good wheat lands for this crop, considering the length of 

 time the plant is engaged in its search. The addition of more of this 

 constituent therefore becomes superfluous in all such cases. With barley 

 and roots it is very different. They both grow rapidly, and depend upon 

 a thinner stratum of soil for their nutrition, hence they at once seize upon. 



