178 ALFALFA FARMING IN AMERICA. 



give phosphoric acid. This acid then unites with lime thrown 

 into the molten metal for the purpose. A phosphate of lime is 

 formed. This rises to the surface of the metal as a fusible slag, 

 and is subsequently poured off and cooled. A dark, brittle, hard 

 mass is obtained, which is capable of extremely fine grinding in 

 roller mills. 



In 1886, Dr. Hilgenstock showed that basic slag phosphate ex- 

 ists as a hitherto unknown compound of phosphoric acid and 

 lime, viz., a tetra-basic phosphate (CaO) 4 P 2 O 5 . Later investiga- 

 tions showed that this phosphate, if only sufficiently ground, 

 passes easily into solution even in very dilute acids. In a sample 

 shaken up with peat and water, 78.8 per cent of its phosphate 

 was dissolved in 14 days. The suitability of basic slag phos- 

 phate for direct absorption by plants was thereby demonstrated. 



The special characteristics of basic slag as a manure are (1) 

 the easy solubility of its phosphate in dilute acid, (2) the pres- 

 ence of free lime giving what is chemically called an alkaline re- 

 action. In both these respects basic slag is superior to bones. 

 Super-phosphate, the other principal source of phosphoric acid, is 

 superior in solubility, being water soluble, but inferior in its 

 general effect upon soils, being deficient in lime. These differ- 

 ences in character of the three manures are seen in their relative 

 effects as crop-producers in carefully conducted experiments. 



The capacity of leguminous crops to utilize atmospheric nitro- 

 gen renders nitrogenous manures generally unnecessary. For 

 the same reason farm yard manure, which supplies much nitro- 

 gen, can in most cases be better utilized upon some other crop. 

 The most profitable return will in ordinary practice be obtained 

 from a dressing of artificials supplying phosphates, potash and 

 lime. 



Beans, vetches and peas are all lime-loving crops, and for this 

 reason basic slag is well suited to their requirements. Belonging 

 to the same natural order are sainfoin, lucerne and clover, im- 

 portant forage crops. For these, 5 cwt. basic slag, and 2 l /2 cwt. 

 kainit in autumn, is recommended as a suitable application, with 

 3 or 4 cwt. superphosphate, and the same quantity of kainit again 

 in spring. The quantities stated may require to be increased or 

 diminished according to the fertility of the land. 



While the necessity of applying manures to land under crop 

 is now almost generally recognized, the claims of pasture 

 strangely enough are almost wholly neglected. Recent investiga- 

 tions have shown, however, that this is a mistake. More es- 

 pecially is this the case with the medium and second-class 

 pastures, whicn form such a large proportion of our grazing area. 



