RELATION OF FERTILISERS TO SOIL FERTILITY. 7 



the presence of this soil toxin the plant removed less phosphoric acid and 

 potash than under normal conditions, but that its absorption of nitrogen 

 was more nearly normal. 



The action of other soil toxins was made the subject of further study* 

 and the following very interesting and rather remarkable results were 

 obtained : Vanillin (an aldehyde) behaves in very much the same way as 

 dihydroxystearic acid in its general effect upon roots and leaves, and its 

 effects are least when the plant is supplied with nitrates. It is pointed out 

 that nitrates increase root-oxidation, whereas both dihydroxystearic acid 

 and vanillin, being capable of further oxidation, are themselves reducing 

 agents. 



Quinone is another organic substance whose presence affects the growth of 

 plants. Unlike the two substances mentioned above, quinone is an oxidising 

 agent, and its ill-effects are less marked when the plant is supplied with 

 relatively large proportions of sulphate of potash, which has a known influence 

 in restraining root-oxidation. 



A fourth substance is coumarin, a substance of fairly wide distribution in 

 the vegetable kingdom, and found to be toxic to many plants. Schreiner 

 and Skinnerj" find that it is particularly toxic to wheat, the leaves being 

 short and broad, and the roots discoloured, and their surface very 

 shiny. The harmful effect of this substance was greatest when phosphoric 

 acid was absent from the nutrient solution, and practically disappeared when 

 the fertiliser was rich in phosphates. The same results were obtained with 

 wheat-plants grown in soil in culture-pots. 



It would, therefore, appear that the bad effects due to the presence of 

 dihydroxystearic acid and of vanillin can be to a large extent neutralised 

 by the application of sodium nitrate, those due to coumarin by phosphoric 

 acid, and those due to quinone by sulphate of potash. With the exception 

 of coumarin, these experiments were carried out apparently only in water- 

 culture experiments, and the point must not be lost sight of that these results 

 when tried in the field may be considerably modified by the chemical or 

 physical nature of the soil. They are sufficiently striking to emphasise the 

 fact that the function of fertilisers is not solely to supply plane-food. 



Fungi Affecting Crops. 



Another way in which one crop may affect injuriously a succeeding crop is 

 by the production of a fungus which infects the soil and attacks the young 

 plants. A fungus of this nature has been found by H. L. BolleyJ to be 

 the cause of what are known as flax-sick soil?, that is soils which after con- 

 tinuous cropping with flax (which does not unduly exhaust the soil) are 

 unable to produce flax. He quotes an experiment in which flax was grown 

 for six consecutive years on a fertile soil of the Red River, the result being 

 that the land was "in such a diseased condition that not a plant of flax 

 can exist on it longer than three weeks from the time of sowing." This 



* Schreiner and Skinner, Bull. 77, U.S.A. Bureau of Soils. 



t Lo<-. cit. 



t Bull. 50, North Dakota Agric. College, 1901. 



