66 



nitrogen to crops, and therefore cannot be used with good 

 effect unless phosphates, and usually potash also, are 

 added to the soil. These mineral manures may often 

 be applied to one crop in the rotation, and sulphate of 

 ammonia to another ; and the minerals may be given as 

 artificials or as farmyard manure, or partly in one form and 

 partly in the other. But at some time in a series of years, 

 and in one or other form, minerals must be given, or the 

 use of nitrogenous manures cannot prove satisfactory. 



SUMMARY. 



I. Sulphate of ammonia is a nitrogenous manure, and 

 must be considered as a source of nitrogen only. 



2. Nine other elements besides nitrogen are essential 

 for plant growth, of which phosphates and potash, 

 as well as nitrogen, must usually be supplied in 

 the manure. 



3. Combined nitrogen only can be used by plants. 



4. Combined nitrogen in Nature is supplied to the soil 

 only in small quantities, and is subject to con- 

 stant loss. The addition of nitrogenous manures 

 is therefore needed. 



5. Nitrogenous manures cause larger leaf growth, in- 

 creased chlorophyll formation, slower maturity, 

 and increased crops generally. 



6. Organic nitrogen is of no direct use to the plant. 

 Nitric and ammoniacal nitrogen are both directly 

 useful, though the latter almost always undergoes 

 nitrification before use. 



7. Ammoniacal manures generally fail to give their 

 maximum result unless potash is liberally supplied 

 by soil or manure. 



3. Sulphate of ammonia reacts in the soil with car- 

 bonate of lime, and carbonate of ammonia is 

 formed, which can then be fixed by the clay and 

 humus of the soil. 



9. Nitrogen may be lost by the volatilization of car- 

 bonate of ammonia, when sulphate of ammonia 

 has been applied to very calcareous soils ; but 

 this is rarely important. 



I0 . Nitrification of ammonia compounds, especially 

 sulphate of ammonia, may be very rapid when 

 everything is favourable. It is more rapid than 

 the nitrification of organic nitrogenous matter. 



ii. After nitrification, the nitrogen is subject to loss 

 by drainage. 



12. Sulphate of ammonia is most effective in wet 

 climates and seasons. 



