Fertilizers and Feeding Stuffs. 361) 



roots of plants, but ammoniacal and certain organic compounds of 

 nitrogen, if applied to the soil, will ultimately be converted by the 

 aid of bacterial organisms into nitrates, so that any of the three 

 classes off nitrogenous compounds mentioned above may be used 

 as sources of nitrogen for plants. In valuing nitrogenous fertilizers 

 it is the amount of the nitrog'en in them that is ascertained as being 

 the essential element common to them all. It must be observed, 

 however, that there are other compounds of nitrogen, such as the 

 sulphocyanides for instance, which are harmful to plants, so that 

 they would be worse than useless foi- fertilizing purposes. 



The element phosphorus cannot be used for application to the 

 soil as a plant food, and there are some compounds of this element 

 which are also strong plant poisons. Phosphorus in combination with 

 oxygen to form phosi)horous pentoxide or phosphoric oxide is an 

 essential constituent of all phosphates, and these are the class of 

 phosphorous compounds utilized as phosphatic fertilizers. Amongst 

 the chief phosphates applied to the soil are the various i)hosphates 

 of calcium, mag-nesium. iron, and aluminium, as they all contain 

 phosphoric oxide — ^that is the constituent estimated in all analyses of 

 such fertilizers and to which monetary value is attached. Potassium 

 is a metal, and as such obviously cannot be utilized by plants as food, 

 but compounds of potassium in the form of salts are usually very 

 soluble, and when present in the soil can be assimilated by plants. 

 For example, potassium combined with the element chlorine forms 

 potassium chloride, and this salt is often applied as a fertilizer. 

 Again, potassium when combined with oxygen forms potassium oxide 

 or potash, and a combination of this oxide with sulphur trioxide gives 

 us potassium sulphate (sulphate of potash), and this salt is also 

 largely used as a potassic fertilizer. Potash combined with carbon 

 dioxide (carbonic acid gas) prtuluces potassium carlionate, which is 

 present to a large extent in wood-ash. another substance applied to 

 the soil very often as a source of potassium. Although the element 

 potassium in the two last-mentioned compounds is present as an oxide 

 (potash), the first mentioned, potassium chloride, does not contain the 

 potassium as oxide at all, and the alternate name of chloride of potash 

 for this compound is a misnomer. It is, however, the practice in 

 analysing this latter substance, after estimating the amount of 

 potassium present, to calculate from it the equivalent amount of 

 potassium oxide and to give the result as so much potash. 



De<fi.)iitio?i of Unit Values. 



It has already been explained that the most important fertilizing- 

 constituents in a manure are : — 



1. Nitrogen, which may be present either as a nitrate, as an 

 ammoniacal compound, or as such organic compounds as the proteins 

 or albuminoids. 



2. Phosphorus, generally in the form of a phosphate, in which 

 Ihe amount of the phosphoric oxide always present is estimated. 



8. Potassium, usually present as a soluble salt, and in which the 

 equivalent amount of potassium oxide or potash is generally given. 

 Therefore, when calculating the value of a manure, only these con- 

 stituents are usually taken into account. 



In valuing a fertilizer it would be possible to calculate, for 

 instance, the price per pound of each of these fundamental con- 

 stituents in it but the more convenient method is to ascertain the 



