104 DEFINITION OF MANUKE 



(1) The addition of substances containing plant food. 



(2) The addition of substances which may act upon the insoluble 

 compounds present in the soil and render available the plant food they 

 contain. 



As to improvement in its biological qualities, little has hitherto been 

 done, but probably in the future, this may be a direction from which 

 considerable help may be derived. 



The destruction of insect pests, and the eradication of organisms pro- 

 ducing diseases in crops or in animals feeding upon the land, are pro- 

 blems which have already been studied with some success. A certain 

 amount of progress, too, has been made in devising means for inoculat- 

 ing the soil or seed with desirable micro-organisms, as witness the 

 commercial production of "alinit" and "nitragin". 1 Proposals to 

 regulate nitrification by the application of antiseptics, so as to lessen 

 the autumnal loss of nitrates in the drainage, have been made - ; but, 

 so far as the author is aware, these methods have not sufficiently com- 

 mended themselves to the practical farmer to be adopted to any extent 

 on the large scale. 



It is with the improvements in the chemical state of the soil that 

 this chapter has mainly to deal. 



These are effected by the application of Manures. The word 

 manure has apparently a connection with the Latin manus a hand 

 and was probably used because of an old belief that the main function 

 of a manure was, by its fermentation in the soil, to aid in the work of 

 pulverisation usually brought about by hand labour, i.e., tillage. 



This aspect of the matter was strongly held by Jethro Tull, who, 

 about the middle of the eighteenth century, wrote a book entitled, 

 " Horse-hoeing Husbandry," in which he attempted to prove that by 

 sufficiently tilling the ground, manures might be rendered unneces- 

 sary. 



" Manure " is no longer used in this sense, but it is now the name 

 given to any material which is intended, by its application to the soil, 

 to restore those constituents which have been removed by cropping and 

 thus to render it possible for the soil to supply another crop with a 

 sufficiency of plant food. 



The constituents of a soil which are most liable to be deficient in 

 amount, and which it is therefore advisable to replenish by manuring, 

 are combined nitrogen, phosphates and potash compounds. 



Manures, therefore, are usually valued according to their richness 

 in these three constituents, though in the case of many so-called natural 

 manures, e.g., farm-yard manure, many other constituents which may 

 serve as useful items of plant food are also present. 



Manures are variously classified ; sometimes in a somewhat loose 

 manner, into 



1. Natural Manures. 



2. Artificial Manures. 



By natural manures are usually meant those produced on the 

 farm itself ; they consist mainly of the remains of plants and animals. 



1 See pp. 65 and 68. 2 Deherain, vide p. 65. 



