112 AGRICULTURE 



to a great extent by the superficial layers 

 of the soil, and therefore does not reach the 

 roots of a top-dressed crop with sufficient 

 rapidity. Of these two manures nitrate of 

 soda is the better for application to the 

 hay crop, and this chiefly because we have 

 hereto do with a crop that can only be manured 

 by top-dressing, so that the added plant food 

 must find its way down through a greater or 

 .less depth of soil before reaching the roots. 

 The superior merits of nitrate of soda, as 

 contrasted with sulphate of ammonia, as a 

 top-dressing for hay, are well illustrated 

 in the long series of experiments conducted 

 on the permanent meadow at Rothamsted. 

 Without exception, nitrate of soda has pro- 

 duced a much heavier crop of hay than 

 ammonium salts, and botanical analysis has 

 shown that the hay is also of superior quality. 

 Nitrogen in the form of ammonia is largely 

 retained in the surface soil, and it has there- 

 fore the effect of encouraging the development 

 of shallow-rooted plants, such as Sheep's 

 Fescue, Agrostis, Yorkshire Fog, Sweet- 

 jscented Vernal, and Smooth-stalked Meadow 

 Grass ; whereas nitrate-nitrogen, by sinking 

 deep into the soil, encourages the growth of 

 plants whose roots are similarly disposed, 

 notably Meadow Foxtail, Tall Oat Grass, 



