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accepted as final; that the work of the field, if it is to have any value, must be con- 
ducted on principles as thoroughly scientific as those which control the most elab- 
orate laboratory investigations, and that when the work is thus conducted it will 
yield results as decisive as those attained in any other line of scientific research. 
And since the existence and increase of the human race depends upon the main- 
tenance and increase of soil fertility, I maintain that this problem transcends in 
importance all other objects of scientific investigation. 
E. B. Voorhees, of New Jersey, read the following paper: 
METnoDs of Conducting Investigations Relating to the Maintenance or Increase 
of Soil Fertility. 
The terms "maintenance" or "increase of soil fertility " have reference, first, to 
methods of practice which may result in changes in the physical character of the 
soil and in the form of the essential constituents — nitrogen, phosphoric acid, or 
potash — and may have no relation whatever to the increase in the soil of potential 
fertility, or, second, to the addition to the soil of actual essential constituents, thus 
adding to potential fertility; or, third, to the addition to the soil of organic matter 
containing nitrogen, which may affect its chemical and physical character, and which 
may also result in the addition to the soil of nitrogen, because of the introduction 
into the soil of living organisms which have the power of fixing atmospheric 
nitrogen. 
Experiments which have for their object the study of any one of these three kinds 
of improvement, to be of service, may be either general or specific. A method of 
inquiry, which is general in its character, does not permit of a close study of the 
reasons for and thus an explanation of the phenomena involved, but has to do 
primarily with results. General methods of inquiry have their place, and a very 
useful one, from the practical standpoint, but it seems to me that they can only be 
regarded as preparatory, and, in a sense, educational, and not for the purpose of 
establishing new facts and principles. 
In the second method of inquiry the work is purely scientific and is planned with 
the specific purpose of enabling an accurate observation of all the changes taking 
place and a control of all of the conditions which are involved. By this method 
pots and cylinders or other means of obtaining small areas are usually included. 
The advantage of this specific method of experiment is that because of an exact 
control of all of the conditions — chemical, physical, and bacteriological — a reason for 
any change which may take place in the soil is suggested, and thus facts and princi- 
ples are established upon which may be based a working theory for the improvement 
of soils in general. 
Nevertheless, I believe that there is a field for general methods of experimentation 
that have for their purpose the improvement of methods of practice and that will 
result in the maintenance or conservation of soil fertility; and whenever it is possible 
to so conduct these experiments as to have the results serve as object lessons, the 
work should not be ignored. As an example of what I mean by this, I may cite an 
experiment very general in its character conducted by our own station on the relation 
of the income and outgo of soils to the improvement or crop-producing power of soils. 
This experiment was planned for the purpose of showing that by the observation of 
natural laws and of the principles already established it was possible to grow profit- 
able crops, while at the same time to maintain or increase active fertility. 
In this experiment three general principles already well established were observed: 
First, that nitrogenous plant food particularly is available in proportion to its solu- 
bility; second, that natural agencies are constantly at work changing dormant con- 
stituents into active or available forms, and, consequently, third, that soils when left 
bare during fall and winter are liable to suffer a loss, not only of the nitrates that 
may have been accumulated during the summer, but also that under such conditions 
of cropping mechanical losses are liable to occur, and that the first parts to be car- 
ried away by the winds or the washing of the winter rains are the finer particles 
which constitute the best part of the soil. Hence, in the experiment the first rule 
adopted was that the land should not lie bare at any season of the year, and if the 
removal of regular crops was so late as to prevent the seeding of a crop that would 
live during the entire winter, such crops were planted as would grow late in the fall 
and remain to protect and mulch the surface soil during the winter and early spring. 
This is to show that the practice would result not only in a saving of the soluble 
plant-food constituents, but would prevent the mechanical waste of soil particles, and 
besides, in case of certain crops, would provide for an accumulation of nitrogen or 
an actual increase in potential fertility. For example, if rye were used in the fall 
losses would be prevented ; the actual gain would be chiefly in the roots and stubble, 
