62 THE CHEMISTRY OF THE FARM 



effect than manures consisting of undissolved phos- 

 phate. A small quantity of phosphoric acid applied 

 as superphosphate will generally have as great an 

 immediate effect as a considerable quantity applied as 

 bones or ground phosphate. 



Superphosphate is chiefly employed for turnips, for 

 v^hich it is invaluable ; it is also of considerable use 

 for corn crops, especially barley and oats. Its use 

 tends to early maturity in the crop. Superphosphate 

 also greatly favours the growth of clover, beans and 

 other leguminous crops. 



Gypsum.— This manure consists of sulphate of cal- 

 cium : it is of very limited value. Gypsum is most 

 suitable for crops, such as clover and turnips, which 

 require a considerable amount of sulphur. On virgin 

 soils gypsum has frequently a wonderful effect on 

 clover. As superphosphate always contains much 

 gypsum, special applications of gypsum will be un- 

 necessary where superphosphate is employed. Finely- 

 powdered gypsum is sometimes employed in stables 

 to hinder the volatilisation of ammonium carbonate. 



Lime, Chalk, and Marl are frequently manures of 

 the greatest importance. On soils naturally destitute of 

 lime, as is the case with many clays, sandstones, and 

 moor soils, these manures will supply an indispensable 

 element of plant food. Some marls will also supply a 

 small quantity of phosphoric acid, and of potash (if 

 glauconite is present). In most cases, however, the 

 beneficial influence of these manures is due to the 

 chemical actions which lime performs in the soil, and 

 to the improvement in physical texture which it pro- 

 duces (see pp. 23, 4G, 56). 



