AUXILIARY AND EXCEPTION'AL MAl^URES. 91 



On wheat or grass land one liundred pounds of sulphate 

 of ammonia or one hundred and fifty pounds of nitrate 

 of soda, per acre, may be used as a top-dressing after 

 early spring growth has commenced; and half as much 

 as a supplementary dressing at a later period, if required. 

 The same quantities will often be bestowed with profit 

 on the root and green crops, giving the first dressing 

 about a month after sowing and the second at the time of 

 the last hoeing. 



Potash Salts. — These are most efficacious on grass 

 land, if well drained, and on light sandy soils. Grasses, 

 potatoes and turnips are particularly benefited by ma- 

 nures of this class. The chief source of supply is kainit. 

 Potash salts in kainit require to be applied to the soil in 

 autumn, giving them time to dissolve in the soil. From 

 one hundred to one hundred and fifty pounds of muriate 

 of potash, or from six to eight hundred pounds of kainit, 

 per acre, are applied in conjunction with other manures. 



Gypsum, or sulphate of lime, is extensively employed 

 as a fertilizer. It enters into the composition of clover, 

 grasses, turnips, and potatoes, but a sj)ecial application 

 of gyj^sum to the soil has little effect in our system of 

 farming. It is abundantly supplied to crops, in the 

 common course of culture, in the farm dung and in 

 superphosphate or dissolved bones and other artificial 

 manures. 



The value of gypsum as a fertilizer is believed to be 

 partly due to its action in fixing volatile and escaping 

 carbonates of ammonia, and conveying them to the roots 

 of plants. When carbonate of ammonia comes in contact 

 with sulphate of lime, double decomposition takes place, 

 carbonate of lime and sulphate of ammonia being formed. 

 Powdered gypsum may thus be used in stables as a fixer 

 of ammonia. It requires to be m a fine state of mechan- 

 ical trituration before it is applied to the soil. 



