1913] SCHREINER— TOXIC SOIL SUBSTANCES. 427 



tivation, or the growth of crops which do not promote deep root 

 growth or active root oxidation. The studies which we have made 

 on soils in respect to their abiHty to oxidize organic substances such 

 as aloin has shown us that fertile soils are generally good oxidizers 

 and infertile soils poor oxidizers. In soils that are good oxidizers 

 the chances of having an undue accumulation or even formation of 

 toxic substances are at a minimum, whereas in poor soils with low- 

 oxidizing power, with low vitality as it were to properly digest the 

 organic refuse of previous growth, harmful substances result. The 

 chief aim in improving unfertile soils should therefore be to build 

 them up so that they will become good oxidizers and through this 

 become strong virile soils. In the laboratory and greenhouse we 

 have been able to observe the disappearance of toxic soil conditions 

 by thorough aeration and exposure to air, by the action of lime, and 

 by the influence exerted by fertilizers, especially the oxidizing fer- 

 tilizers like sodium nitrate, or the catalytic influence of oxidizing 

 substances like manganese. In the field the most useful agents are 

 (i) better drainage, which promotes better aeration and increases 

 the oxidation in the soil; (2) liming, which in addition to neutraliz- 

 ing acid tendencies, or combining with the substances to form insol; 

 uble or inert compounds, has also the efifect of increasing the oxida- 

 tion in the soil and in the plant roots as well as to have a physio- 

 logical effect on the plant cells themselves which makes them more 

 resistant to poisons in general; (3) crop rotation, which gives to 

 the soil each year a different kind of organic debris, changing as it 

 were, the normal food of the soil, from time to time, and further- 

 more necessitates different cultural methods and different fertiliza- 

 tion systems, alternating cultivated crops with uncultivated crops, 

 shallow rooted plants with deep rooted plants, grain crops with root 

 crops, leguminous with non-leguminous crops, with the result that 

 the biochemical changes in the soil, the digestion, the oxidation, the 

 catalysis, of the soil, proceeds in a normal manner, the balance of 

 soil factors being influenced in a favorable direction and a healthy 

 normal soil results ; and (4) fertilization, which is usually done with 

 the motive of adding plant food, but which the more modern inves- 

 tigations in biological and biochemical fields are showing to be an 



