166 NITEATE OF SODA OE SULPHATE OF AMMONIA 



can only successfully be applied to soil containing a sufficiency of cal- 

 cium carbonate, and its repeated application entails a considerable loss 

 of lime (equal to 100 of calcium carbonate for every 132 of sulphate of 

 ammonia applied, or if the lime required for nitrification be included, 

 twice this amount) in the drainage water : 



(NH 4 ) 2 S0 4 + CaC0 3 = CaSO 4 + (NH 4 ) 2 CO 3 and 

 (NH 4 ),C0 3 + 40 2 + CaC0 3 = Ca(N0 3 ) 2 + 2CO 2 + 4HX>. 



Soils deficient in lime compounds can be more suitably manured with 

 nitrate of soda. 



2. Nitrate of soda is easily washed into the subsoil by rain, and in 

 wet seasons a considerable amount of it is lost. It should only be 

 applied when the plant can assimilate it. Sulphate of ammonia, 

 though equally soluble in water, is not washed out by rain to any ap- 

 preciable extent, but is held by the humus and perhaps by the hy- 

 drated' silicates and the ferric hydroxide until nitrification occurs. For 

 this reason, sulphate of ammonia is most useful to shallow-rooted plants, 

 while nitrate of soda tends to encourage deep rooting. Sulphate of 

 ammonia is therefore preferable in wet seasons and gives the best re- 

 sults when applied at the time of sowing, or even before. Nitrification 

 can only take place in the presence of sufficient, and is favoured by 

 increased, moisture, short of complete saturation, so that in dry seasons 

 sulphate of ammonia is not so suitable as nitrate of soda. 



3. On soils very rich in calcium carbonate, ammonium sulphate, if 

 used as top dressing, may suffer decomposition with loss by volatilis- 

 ation of ammonium carbonate, especially in dry weather. This loss 

 can be prevented by ploughing or harrowing the sulphate into the soil 

 immediately after its application. 



4. Both nitrate of soda and sulphate of ammonia will only yield 

 the best results when the soil is abundantly supplied with the neces- 

 sary mineral constituents of plant food. 



With sulphate of ammonia, however, it is more necessary to supply 

 potash, for with many soils, the use of nitrate of soda appears to render 

 potash manuring unnecessary, at least, for a time. This may be due 

 to its action in favouring deep rooting, the necessary potash being ob- 

 tained from the subsoil, or partly to its action in rendering the potash 

 of the silicates of the soil more available or, perhaps to the possibility 

 of sodium performing, to some extent, the functions of potassium, in 

 the plant itself. 



5. Nitrate of soda is best applied in several small dressings, while 

 sulphate of ammonia may generally be applied in one. The usual 

 quantities are from 1 to 1J cwt. of the former and 100 to 150 Ib. of 

 the latter per acre, but with certain crops, e.g., mangolds and potatoes, 

 larger quantities may be used. 



6. Nitrate of soda, by repeated applications, has a strong defloccula- 

 ting effect upon clay and thus injures the physical or mechanical pro- 

 perties of some soils. 



7. The repeated application, year after year, of sulphate of ammonia 

 to grass land, tends to induce an acid or peaty character in the surface 



