RELATION OF FERTILISERS TO SOIL FERTILITY. 11 



carbon, toluene, &c. (such vapour being subsequently removed by spreading 

 the soil out in a thin layer and allowing the vapour to evaporate), the effect 

 is to destroy the protozoa and probably most of the bacteria as well, but 

 not the spores of the ammonia-producing bacteria. These spores subsequently 

 develop, and in the absence of the hostile protozoa, their development 

 proceeds with increased activity, the result being a considerable increase 

 in the soluble nitrogenous plant-food and a more vigorous crop growth. 



These experiments have so far been carried out in the laboratory. If 

 means are discovered of partially sterilising the soil in the field, a most 

 valuable method of increasing the fertility of the soil will be placed at the 

 disposal of the farmer. 



Indeed, experiments in this direction have been recently carried out by 

 E. J. Russell and J. Golding* on " sewage-sick " soils. They find that 

 "sewage-sickness" is an abnormal development of the factor harmful 

 to bacteria (protozoa) always present in ordinary soils, and that the 

 loss of efficiency in the purification of sewage in such soils is due to 

 the hindrance of the development of the bacteria. Small land-filters were 

 made in the field, some being filled with untreated soil and others 

 with treated or sterilised soil. The effluents were examined periodically. 

 The untreated samples soon became " sewage-sick," whereas the effluents 

 from the treated filters retained their efficiency for months!. A further 

 experiment was tried by treating small plots in a similar manner, the plots 

 being then sown with turnips. The crops on the treated plots (especially 

 that treated with toluene) were not only better than those from the untreated, 

 but suffered much less from " finger and toe." 



Further interesting trials were recorded by E. J. Russell and F. R. 

 Petherbridgef of the action of heat and antiseptics upon sickness in 

 glass house soils. In countries where plants like cucumbers and tomatoes 

 are grown under glass, the soil is found to bs unsuitable for the growth of 

 these plants after a short time, sometimes after the first crop. The soil 

 used is therefore thrown away, and as it is necessary to enrich it very much 

 with manure and to expend much time and labour on i's preparation, this is 

 a very wasteful operation. The authors find that previous steaming of the 

 sick-soil of a commercial glass-house in which cucumbers were grosvn, 

 resulted in curing the soil of cucumber-sickness and rendering it once more 

 commercially profitable. The s *me was found to be the case with tomato- 

 sick soil on which a number of different antiseptics were tried. Of all 

 methods, .heating the soil to 98 was found to be the most effective. 

 The cost of this operation is from Is. to If. 6d. per ton of soil, which while 

 profitable in the case of plants grown under ghss, is quite prohibitive on 

 large areas. 



S. U. PickeringJ considers that on heating a soil the amount of soluble 

 plant-food is increased, and the changed bacterial conditions studied by 



* Journ. Aqric. Science, vol. 5, p. 27. 



t Ibid., p. 86. 



Journ. Ayric. Science, vol. 3, p. 277. 



