IMPROVEMENT OF SOILS. 109 



the necessary micro-organisms or their spores are 

 present. Even more dependent upon the presence of 

 suitable micro-organisms is the utilisation of the free 

 atmospheric nitrogen by the leguminosas. Fungi, 

 yeasts, other low forms of life, as well as worms, cater- 

 pillars, larvae, &c., also play an important part in alter- 

 ing both the physical and chemical properties of soil. 

 Unfortunately, in the case of the latter organisms, 

 their influence on the plant itself often exceeds in 

 importance their effect on the soil. 



Improvements in the soil are naturally the aim of the 

 agriculturist. As regards its physical condition, much can be 

 done by tillage operations ploughing, harrowing, draining, 

 &c. also by the introduction of materials which affect the 

 mechanical properties of its constituents, e.g., lime, bulky 

 vegetable refuse, &c. 



With reference to the actual plant food in a soil, improve- 

 ments can be effected in two ways 



(1) The addition of substances containing plant food. 



(2) The addition of substances w r hich 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 in the future, probably, this may be a 

 direction from which considerable help may be derived. 



The destruction of insect pests, and the eradication of 

 organisms producing diseases in crops or in animals feeding 

 upon the land, are problems which have already been studied 

 with some success. A certain amount of progress, too, has 

 been made in devising means for inoculating the soil or seed 

 with desirable micro-organisms, as witness the commercial 

 production of " alinit" and " ni^ragin."* Proposals to regu- 

 late nitrification by the application of antiseptics, so as to 

 lessen the autumnal loss of nitrates in the drainage, have been 

 made;t but, so far as the author is aware, these methods 



* See pages 80 and 81. t Deherain, v. p. 68. 



