-4 



It should not be forgotten that there are numerous 

 other micro-organisms in the soil, many of which are not 

 only useless to plant life, but may be actually injurious 

 particularly by preventing the full development of the 

 nitrifying bacteria. Dr. E. J. Russell, of the Rothamstead 

 Experimental Station, has discovered that if soil is par- 

 tially sterilised, either by steam or by volatile disinfect- 

 ants, some at any rate of the harmful organisms are 

 destroyed, and the subsequent activity of the useful 

 bacteria is greatly increased. The effect of such partial 

 sterilisation has been found particularly beneficial in the 

 case of richly cultivated soil, such as that in use in green- 

 houses and market gardens, and sterilisation has been suc- 

 cessfully adopted in many instances. The chemical 

 antiseptic used by Dr. Russell was toluene, one of the 

 coal tar products. Its action as well as that of steam is 

 generally believed to destroy the numerous protozoa, which 

 are microscopic animal organisms. Some of these are 

 known to feed on bacteria, and are therefore very likelv 

 destructive of the nitrifying bacteria.* 



Before leaving the subject of the nitrogen nutrition 

 the chief function of the roots of plants, it should be 

 mentioned that excessive use of nitrogenous manures has 

 been found to render many plants more liable to disease, 

 particularly such as are produced bv various fungi. It 

 is well, therefore, to practice moderation. 



As regards other substances than nitrogen which it 

 has been found useful to add to the soil as fertilizers, 

 the most important are potash and phosphoric acid, the 

 latter in the form of various phosphates, including bone 

 meal. 



These plant foods must be used in differing propor- 

 tions according to the richness of the soil, and also 

 according to the requirements of particular crops. Speak- 

 ing generally, gardens and allotments which receive an 

 abundance of stable manure do not require much in the 

 way of other fertilizers : but in heavy soils basic slag 

 used occasionally will be found a useful w^ay of adding the 

 necessary phosphorus, while nitrate of soda is often valu- 

 able to push on early crops, such as lettuces, peas, etc. In 



See Reports on the Partial SteriHsation of Soil " Journal 

 of the Board of Agriculture, January, 1912, January. igi3, and 

 May, 1914. 



