A contribution to our knowledge of the protozoa of the soil

Abstract
In the ‘Journal of Agricultural Science,’ Vol. III, Part 2, 1909, Drs. Russell and Hutchinson of this laboratory published an account of their investigations on the effect of partial sterilisation of soil on the production of plant food. In this paper it is shown that, when soils are heated or treated with certain volatile antiseptics, and brought again under conditions favourable to plant growth, they show a great increase in fertility. It is further shown that, although the bacteria are at first reduced very considerably in numbers, yet under conditions of temperature, moisture, and aëration favouring growth, they subsequently increase enormously in numbers.Pari passuwith this increase in the number of bacteria, there is an increase in the production of ammonia in the soil, and it is to this that the soil owes its greater power of production. In explanation of these results, the theory is advanced that the treatment by heating or with antiseptics has removed some factor which in the untreated soil normally limits the growth of bacteria, and thus the rate of ammonia production. This limiting factor is looked upon as being biological in character, but not of a bacterial nature.