128 AGRICULTURE 



ated with superphosphate. Basic slag is 

 pre-eminently adapted for use upon grass land, 

 and especially on land that has for some years 

 been under pasture. Probably one reason 

 why basic slag is capable of exerting its best 

 effects on old grass land is that under such 

 circumstances the soil contains a consider- 

 able amount of humic and carbonic acids, 

 which are formed during the decomposition 

 of the vegetable matter. These weak acids 

 react upon the slag, and appear to be sufficient 

 to make a large proportion of the phosphate 

 immediately available for the use of plants. 

 While basic slag generally produces superior 

 effects on grass land, it must be said that its 

 action is most of all emphasized where there 

 is any tendency towards sourness in the soil. 

 This condition of things is indicated by the 

 presence of certain plants, such as Bent Grass, 

 and more particularly the so-called Carnation 

 Grass (Carex glauca). Whereas superphos- 

 phate, being an acid substance, increases the 

 acidity of soil, basic slag, being alkaline, tends 

 to counteract acidity, and this action is to 

 the advantage of all crops. 



It is often asserted that basic slag has little 

 effect on grass land where the soil is sandy 

 or gravelly, or even where there is a marked 

 tendency in this direction. Under these 



