MICHIGAN ACADEMY OF SCIENCE. 
61 
and freshly fertilized field is better suited to crop production than a 
virgin prairie, but also more sensitive to mistakes in management or 
judgment. Far too often is the soil blamed for the shortcomings or 
errors of the farmer. By slight changes of condition in the laboratories 
we can induce a seedling plant to grow long or short roots as compared 
with the tops ; but does any one yet make use of this knowledge in grow- 
ing a field of wheat? Mineral nutrients are essential to metabolism in 
all organisms, but is it not foolish to pin our faith on this alone, when 
for instance it has been shown that the ragweed following a wheat crop 
takes out of the soil more of the mineral nutrients than does the wheat 
crop. Rather is it not more reasonable to infer that the inability to 
produce a satisfactory repetition of the wheat crop is due to the fact 
that so artificialized a plant as the wheat, in which habits have been 
bred into characteristics, can thrive only under a special combination 
of soil, climate and seasonal factors which can not be realized in the 
soil from which the crop has just been removed. 
We are led here to consider another important generalization which 
has not received the consideration it should. It is a characteristic of 
all activities, physical, chemical or biological, that as the activity pro- 
ceeds in any definite direction, products of the activities accumulate and 
slow up the action, ultimately stopping it if the products are not re- 
moved. This generality holds for waste products or so-called by-products 
as well as for the main ones. The factory cannot continue unless by- 
products are removed. Manure must sometime be removed from the 
barnyard. Every housewife knows that the kitchen cannot be managed 
without removal of the garbage. In chemistry we have the well known 
law of mass action which in different forms has its application in physics 
and biology. The bacteria or the yeast cannot continue to live and thrive 
when the medium in which it exists reaches a certain concentration with 
respect to its reaction products, a familiar example being the fermenta- 
tion of sugar to alcohol. But some other ferment can, however, live and 
thrive in the medium, as the butyric acid ferment. Rats are said to be 
able to live in an environment which man or some other higher animal 
has fouled beyond the point of habitability. 
So with our crop plants. Because of their higher artificiality they are 
the more prone to unfit their environment for continued production, 
unless the environment be artificially assisted by suitable management, 
and to this end we must investigate the causes, whether toxic organic 
substances, disturbed bacterial associations, or whatever they may prove 
to be in any particular case. The principle to which the president of fhe 
American Chemical Society called attention recently as a universal law, 
finds ready application here. The ragweed requiring as much “food" 
and water as the wheat will grow in the soil which cannot hr replanted 
to the latter, but (in certain regions which have been under my own 
observation at least) the ragweed itself gives place the following spring 
to blue grass. 
What then is the theory of soil management? Tn the sense of a simple, 
formal statement, there is no theory. At the best such statements can 
be but a part of the whole truth which is the basis of soil management. 
It is never true that the crop growth is or would be determined by a 
minimum content of any one mineral element or by a maximum content 
of some organic substance, or by a given ratio of protozoa to bacteria 
