Manures and Manuring 145 



2. KINDS OF MANURES 



Long before agricultural chemistry was thought of there were practi- 

 cally only two kinds of manure in use farmyard or stable manure and 

 lime. These constituted the stock of the farmer and market gardener, 

 but other odds and ends were added to soil in the way of waste materials. 

 With the advance of botanical and chemical science, however, plant-growers 

 have been made aware of the different constituents of plants, and numer- 

 ous experiments proved that from twelve to thirteen different ingre- 

 dients (see p. 108) were always found in plants, and had to be supplied. 

 Of these the most important are the nitrates, phosphates, potash, and 

 lime. Hence manures are now classified in accordance with the amount 

 of food they supply as nitrogenous, phosphatic, potassic, and calcareous. 

 Natural manures supply all these foods in small quantities in proportion 

 to their bulk, but they must not be despised on this account. The 

 advantages of complete, bulky manures are discussed under the heading 

 of " Farmyard Manure " below, and these advantages exist to a certain 

 extent in all organic material placed in the soil for manurial purposes. 

 Artificial manures, on the other hand, supply large quantities in proportion 

 to their bulk of one or more fertilizers, and therefore have to be used with 

 caution. And they possess not only this disadvantage, but others. They 

 supply no humus to the soil, and consequently are incapable of generating 

 bacteria. Their application is often of what may be termed a purging 

 nature, because they liberate too freely large quantities of valuable foods 

 that cannot be absorbed by the roots of plants, and are therefore lost 

 either in the drainage or as gas that escapes into the air. Thus it may 

 happen that a soil, instead of being enriched by applications of chemical 

 manures, may be quickly impoverished and rendered sterile. In practice 

 this is actually the case when chemical manures are applied injudiciously 

 or indiscriminately. 



From a practical standpoint it may be more convenient to consider 

 the various manures under the following headings: 



1. Complete Manures. Those supplying not only nitrogen, potash, phosphates, 

 and lime, but also the other essential foods like sulphur, iron, magnesia, soda, 

 chlorine, &c. 



2. Nitrogenous Manures. Those chiefly supplying nitrogen. 



3. Phosphatic Manures. Those chiefly supplying phosphoric acid. 



4. Potash Manures. Those chiefly supplying potash. 



5. Calcareous Manures. Those supplying lime or chalk. 



6. Miscellaneous manures, such as sulphate of iron, salt, &c. 



VOL. I. 10 



