PREPARATION OF SOILS FOR CROPS 253 



after nitrification in a more available condition as 

 plant food 91 . The mineral as well as the organic 

 matter of the soil is subject to the action of micro- 

 organisms, and the cultivation which the soil receives 

 can be made either to accelerate or to retard this 

 action. Many of the chemical changes which take 

 place in the soil resulting in the liberation of plant 

 food are induced by micro-organisms, hence the rela- 

 tion between cultivation of the soil and bacterial 

 action. Each type of soil has its own characteristic 

 microscopic flora. 



339. Inoculation of Soils. In old soils where 

 the process of nitrification is feeble, it has been pro- 

 posed to inoculate the soils with more active forms of 

 bacteria so as to make the inert humus nitrogen more 

 available as plant food. In order to secure the best 

 results from inoculation, suitable food must be sup- 

 plied for the organisms and any adverse condition, as 

 excess of acids or alkalies, must be corrected. Most 

 soils contain the requisite soil organisms but frequently 

 they are unable to do their work because of unfavor- 

 able soil conditions, as the presence of injurious matter 

 or the lack of cultivation or food. For the production 

 of legumes, inoculation of the soil is often beneficial. 

 The commercial production and distribution of the 

 organisms forming the nodules on the roots of clover 

 and other leguminous crops and which cause fixation 

 of atmospheric nitrogen, was first proposed and inau- 

 gurated by Nobbe 94 ; later a modified form of soil in- 

 oculation was proposed by Moore 87 . The method 



