428 SCHREINER— TOXIC SOIL SUBSTANCES. [April 18, 



accessory to proper soil treatment because in addition to supplying 

 needed plant nutrients they influence the microorganic life within 

 the soil, because they influence the oxidation in the soil, the catalysis 

 in the soil, the digestive processes in the soil, so that the biochemical 

 processes are altered, the balance of factors influencing plant growth 

 is changed, because they influence the oxidation of plant roots, and 

 because, directly or indirectly, they effect the destruction, the neu- 

 tralization, or prevent the formation of harmful substances. I have 

 not considered here the mechanical composition of the soil particles, 

 the big natural agencies which have operated to form soils, the loca- 

 tion or topagraphy of the lands and the normal water capacity of 

 soils, the origin of soils, or their relation to climate and rainfall, all 

 of which factors influence soil type and contribute to make some 

 soils naturally more fertile than others, naturally adapted for the 

 growth, and sometimes the continuous growth of one crop, while 

 unsuited to another, facts which must receive more and more atten- 

 tion in the future if we are to get the maximum returns from our 

 soils. I am considering only the means which will tend to maintain 

 or increase the fertility to a status normal to that kind of soil, to 

 maintain it in a healthful, virile state. 



The great question before scientific agriculture is not whether 

 fertilizers are helpful, no more than modern medical science con- 

 siders whether foods or medicines are helpful, but rather how^ can 

 these be made more efficient, more certain in their action, more spe- 

 cific in their application to the needs of the soil. Soil students 

 have in the past century contented themselves practically with a 

 single factor of soil infertility, a not unimportant factor it must be 

 admitted, but nevertheless one insufficient to explain all difficulties, 

 namely, that of plant starvation, the question of lacking plant food. 

 The studies have centered about the food of the plant w'hile the sur- 

 roundings, the home of the plant, the soil itself, has been virtually 

 ignored, or given only minor consideration, except as a storehouse 

 for plant food. Even in the more scientific work of the past decade 

 in reference to bacteria, and other biological work, the production of 

 plant food has been the motive of all study and all discussion is from 

 the point of view of liberating potash, phosphate, or increasing the 



