16 The Profitable Culture of Vegetables. 



Soil Bacteria. The soil is not merely an inert mass of 

 material serving as an anchorage for plants and a storehouse 

 of the food which the plant requires. It is a complex workshop 

 where many diverse processes are continually taking place. 

 Many of these processes are chemical, whereby the mineral 

 compounds derived from the rock debris which forms the base 

 of soils are brought into the condition of solubility. But there 

 are also many other processes which are not of a chemical 

 nature. The surface soil is continually receiving additions of 

 organic matter, such as decaying vegetation, falling leaves, the 

 droppings of animals and birds, as well as the manures supplied 

 during the operations of cultivation. These organic materials 

 rapidly change into the dark-coloured body known as humus, 

 which in its turn is further changed into carbonic acid, water, 

 and nitric acid. All these changes in the form of organic 

 material are brought about by certain minute micro-organisms 

 known as soil bacteria. 



These bacteria are universally distributed throughout cul- 

 tivated soil ; any soil in which they are not present would be 

 sterile. They occupy the surface soil in almost countless 

 numbers, as many as four millions having been estimated to 

 occupy one cubic inch. Below the fertile surface soil they 

 rapidly become less in number, comparatively few being 

 present in the subsoil, which helps to explain why subsoil is 

 sterile when brought to the surface before deep cultivation 

 has had time to make it into a suitable breeding place for 

 bacteria. These organisms are most active in a temperature 

 of 65 degrees F. They cease to work when the temperature 

 falls below 10 or rises above 100 degrees. To enable them to 

 properly perform their functions it is necessary that the soil 

 should be warm, moist, and well aerated, also that a certain 

 amount of lime is present as a base to neutralise the acids 

 which they produce. 



Another variety of these bacteria enters into a sort of joint 

 existence with plants of the leguminous species (peas, beans, 

 clover, tares, &c.) directly helping them to draw from the 

 atmosphere the nitrogen which they require. The bacteria 

 form colonies or communities in the nodules (little warts or 

 lumps) which are more or less present on the roots of all 



