MICHIGAN ACADEMY OF SCIENCE. 
59 
responsiveness to a given tillage method or fertilizer treatment. In 
other words, soils are highly individuated, a fact not generally recog- 
nized, but of the first importance to an intelligent and rational manage- 
ment. 
Let us turn now to a consideration of the instruments or methods of 
soil management. As stated before, these may be classified under three 
general heads, tillage, crop rotations, and fertilizers. The essential fun- 
damental facts which it is important to bear in mind here is that no one 
of these methods can be expected to take the place of the others, although 
they do all affect the same natural factors and consequently are thus 
mutually interdependent. Tillage obviously affects the physical proper- 
ties of the soil, but it affects also the chemistry of the soil, for the altered 
movements of water, of carbon dioxide content of air, and possibly other 
relations in the soil affect profoundly the inorganic and organic relations. 
No less profoundly are the bacterial flora and other biological features 
affected. But fertilizers, as recent investigations are making obvious, 
produce as profound changes in the physical properties of a soil as do 
tillage operations, and that they affect the chemistry and biology of the 
soil no one can question. Nevertheless in their net results we must con- 
sider tillage and fertilizers as differing not only in intensity or amount, 
but essentially in kind. Two great errors with their attendant lessons 
are before the American public at the present time. In the South 
Atlantic States tillage has been, speaking generally, poor and unsatis- 
factory. rotations uncommon, and the dependence is upon fertilizers 
under the mistaken idea that plant foods alone are what the soils need. 
In the trans-Mississippi areas generally rotations are again neglected, 
fertilizers are seldom used because of the supposed superabundance of 
plant foods or “fertility,” and the dependence is alone or almost entirely 
on tillage. 
Time will not permit of any great amplifications of these illustrations, 
but abundant evidence is coming to hand that both procedures are at 
fault. The introduction of diversified methods of farming and better 
tillage in the South has established beyond question that the soils of that 
region have a value for crop production immeasurably higher than the 
popular notion. The increasing demands for the lands of the western 
States has directed attention to their yields. There is a popular impres- 
sion that these yields are falling off — a doubtful opinion in view of such 
official records as are available, but it is certain that they must increase 
to justify the continuance of their relatively high money value, and if 
they are to meet the growing demands of an increasing population. The 
lessons which these considerations teach are sufficiently clear. Modifica- 
tions of tillage methods, introduction of new fertilizer materials, adapta- 
tion of rotations to special soil peculiarities, climatic environment or 
market conditions will undoubtedly be worked out for each locality, but 
essentially the principles are the same. 
It is an interesting fact worthy of the most serious consideration of 
both the scientific investigator arid the practical layman that we have no 
definite idea as to the limit of productivity of which soils are capable. 
Under greenhouse and laboratory conditions yields can be obtained 
enormously higher than are actually gotten in the field. This is contrary 
to the general rule in industrial operations. It is well established that 
the factory practice is more efficient than the laboratory. For example, 
