18 



THE AGRICULTURAL NEWS. 



Jasuaey 22, 1910. 



A careful consideration of the history of a given 

 area of soil makes it evident that it is in a constant 

 state of change. In some respects it is undergoing 

 a loss of actual matter, in others a gain of material is 

 being made. As regards the first, water is always 

 leaving it, through evaporation and transpiration by 

 plants, as well as through drainage and percolation, 

 the latter circumstances leading to a loss of soluble 

 matter, in addition, while where the rainfall is heavy, 

 there is a likelihood of a loss of bulk taking -place 

 through the washing away of the smaller, lighter 

 particles. To these more mechanical causes of loss are 

 added those of the action of denitrifying and, in 

 many cases, putrefactive organisms, whereby nitrogen, 

 carbon, oxygen and hydrogen are removed. Loss also 

 takes place to a certain extent by the removal of such 

 parts of plants as are carried away by the wind or by 

 ^nimals: by the former in connexion with the distribu- 

 tion of seed, and by the latter through accident, or 

 purposely, for the provision of food, clothing, etc. 



Considering again a .definite area of soil, one of 

 the chief sources of addition is, of course, the water 

 which falls as rain, bringing with it the gases which it 

 has dissolved during its journey through the atmo- 

 sphere: through the air also arrive particles of matter 

 and portions of plants which have been carried by the 

 wind from other areas of soil. From below, it receives 

 increments of matter by the weathering of the subsoil 

 and underlying rocks. The carbon and much of the 

 oxygen which are supplied in the remains of the plants 

 that have lived and died upon it are an addition 

 from the air. Nitrogen is added by the nitrogen-fixing 

 bacteria and by those which live in symbiosis with 

 leguminous plants. Lastly, matter is added to the soil 

 by animals, either accidentally, or (as in the case of 

 man) for the purpose of increasing the yield of the 

 crops which grow on it. 



An appreciation of these facts will lead to an 

 understanding of the phenomena which are exhibited 

 by the soil when it is subjected to different kinds of 

 treatment. One of these, which has lately aroused 

 particular interest, is sterilization, whereby the soil 

 is placed under such conditions that the forms of 

 life in it are partially or completely destroyed; it 

 is now proposed to give more definite attention to 

 this. A first effect of sterilization to be noticed was 

 the increased fertility of the soil which followed it — 

 a circumstance original!}' observed by Oberlin, when 

 using carbon disulphide as a remedy against the 

 phylloxera of the grape. Since then, investigations 

 have been conducted with other sterilizing agents such 

 as benzerje, ether, chloroform, toluene and phenol, as 



well as in experiments where heat was employed; in 

 the last connexion, Russell and Darbishire, in England, 

 carried out an exhaustive series of trials by which they 

 showed that heated soil will produce a yield twice as 

 great as that from un heated soils, and that the effect 

 of the heating will declare itself during four subsequent 

 crops. Without such researches, the broad fact that 

 soil which has been heated gives larger crops has long 

 been evident to those who have observed plants grow- 

 ing on the sites where weeds have been burnt, or where 

 charcoal pits have been made. It is not, however, 

 a simple matter to provide an adequate explanation of 

 the circumstance. 



In the attempt to do this, various theories have 

 been put forward: they may be divided into those which 

 advance direct action of the disinfecting influence on 

 the soil as the cause of the phenomenon, and those which 

 attempt to explain it through its effect on the organisms 

 in it. In the first division are included those of Moritz 

 and Scharpe, and Pickering. The former endeavour to 

 explain the action of carbon disulphide, in the connex- 

 ion, by stating that this substance becomes changed 

 into bodies suitable for plant food, in the soil — an 

 occurrence which is very unlikely to take place, in 

 consideration of the stability of that compound and of 

 the small likelihood that it can be decomposed by 

 bacteria. Pickering (see Agricultural News, Vol. 

 VIII, p. 281) only goes as far as to draw a comparison 

 between the action of disinfectants and that of heat in 

 increasing the amount of the soluble organic matter in 

 the soil. 



Other explanations, as has been stated, have for 

 their basis the alteration of the conditions in the soil 

 as regards the micro-organisms which it contains. 

 Hiltner and Stfirmer arrived at the conclusion that 

 partial disinfection of the soil upsets the balance of 

 bacterial life in it, with the effect that improved con- 

 ditions arise on account of the resulting increase in 

 numbers of the beneficial varieties of bacteria. Koch 

 has suggested that the change is due to stimulation of 

 bacterial growth, in the case of disinfectants, by the 

 traces of those bodies which remain in the soil after 

 their use, basing his theor}- on the well-known fact 

 that poisonous compounds, in small quantities, often 

 act as stimulants. Loew explains that, as the walls of 

 dead cells permit the passage of all kinds of dissolved 

 matter, owing to the destruction of the lining of 

 protoplasm, the contents of the dead organisms pass 

 out into the soil, thus enriching it chiefly with 

 nitrogenous compounds and potassium phosphate, 

 the process being aided by the property possessed by 

 certain bacteria of producing enzymes (ferments )^which 



