14 
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 likely 
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 by 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 
ei 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 way 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 Sterilisation of Soil ” Journal 
of the Board of Agriculture, January, 1912, January. 1913, and 
May, 1914. 
