VIII. APPLICATION OF MANURES 165 



Nitrate of soda is almost always used as a top dressing, and, as a 

 rule, it should not be applied to a soil until the crop is sufficiently well 

 provided with a root system to permit of the fertiliser being absorbed 

 by the crop. If applied too early, there is great risk of loss through 

 leaching. For the same reason, several small dressings are more 

 economical than the same weight applied at once. 



From J to 1 cwt. per acre, applied in spring, is usually the 

 dressing for cereals, but in the case of barley for malting purposes, 

 only limited supplies of nitrates should be given or the quality of the 

 grain may suffer. 



On permanent meadows, up to 2 or 3 cwt. is often used, best 

 applied in two or three dressings, but if farm-yard manure has been 

 applied recently, not more than 1 cwt. should be used. 



For mangolds and cabbages, 4 cwt. or more per acre is often 

 employed with advantage. 



For turnips, swedes and potatoes, about 1 cwt. is usually em- 

 ployed, of course along with other manures. In orchards, nitrates 

 should be very sparingly used, if at all, or abundant woody growth 

 and little fruit will be produced. 



(b) Sulphate of ammonia. The sources and preparation of this 

 manure and of nitrate of soda have already been described (vide p. 132). 

 Owing to its greater concentration in nitrogen, less total dressings than 

 with nitrate of soda are usually employed ; theoretically 66 Ib. of sul- 

 phate of ammonia contain the same amount of nitrogen as 85 Ib. of 

 nitrate of soda, so that the equivalent of 1 cwt. of the latter would be 

 86-8 Ib. or 0'776 cwt. of sulphate of ammonia. In practice f cwt. is 

 often taken as equivalent to 1 cwt. of nitrate. 



Since, in most cases, the utilisation of sulphate of ammonia by 

 plants has to be preceded by its nitrification, it does not act as such a 

 powerful stimulant to plant growth as nitrate of soda, but in suitable 

 soils affords a steadier and more sustained supply of nitrogen. For 

 this reason, and also because it suffers much less loss by being 

 washed out in the drainage water, it can, with economy, be applied in 

 relatively larger dressings at a time. But due regard must be paid to 

 the demands which it makes upon the soil for lime, in order to allow 

 of its nitrification. 



Comparative Merits of Nitrate of Soda and Sulphate of Ammonia. 



Numerous experiments on the relative advantages of nitrate of 

 soda and sulphate of ammonia as sources of nitrogen have been made. 

 The general results may be summarised thus : 



1. Nitrate of soda is quicker in its action, being already capable of 

 yielding its nitrogen to the crop. Sulphate of ammonia must first 

 undergo nitrification in the soil before it can be utilised to any extent 

 by the plant. For this process to occur it is necessary that some basic 

 material (generally calcium carbonate) be present in order to (1) com- 

 bine with the sulphuric acid of the sulphate (the calcium sulphate 

 formed is carried off in the drainage water), and (2) assist in nitrification 

 by forming calcium nitrate. For these reasons, sulphate of ammonia 



