18 BULLETIN 1419, U. S. DEPARTMENT OF AGRICULTURE 
requirements of different crops are not the same. Meadows require 
a water level near the surface; pastures are more profitable with a 
lower water table; cultivated farm and garden crops usually need a 
much greater depth to ground water. The position of the water 
level influences also to a marked degree the penetration of heat and 
the effect of frost. The fact is well known that crops on peat lands 
are more seriously damaged by frost than those on mineral soils. 
Although the frost hazard can be reduced by using fertilizers, by a 
thin surface coating of clay, sand, or loam, and by more hardy crops 
in the rotation, it can be further lessened by better control of the 
soil moisture. If the water table is properly lowered, peat land can 
be compacted and cultivated earlier in the spring. Moreover, deep 
drainage during winter favors* a deeper aeration and disintegration. 
Unaerated, water-soaked layers, on the other hand, show a tendency 
toward leaching and corrosion. The extent of the injurious effects 
is often difficult to determine, particularly the corrosion of tile drains 
and cement foundations. In this connection, it should be kept in 
mind that the moisture content present in the profile section does 
not depend altogether upon the distance to the ground-water level 
but in part upon the character of the peat layers and the stage of 
disintegration. Hence methods of aeration and cultivation should 
be adapted to the structural profile features, in order to alter the 
respective water-holding capacity of the different types of peat land. 
EFFECTS OF THE MINERAL SUBSTRATUM 
The widely differing profile features of peat lands point to the fact 
that during the formation of a peat deposit the plant tissues and 
other organic remains in layers of peat are not greatly altered 
by chemical or bacterial action. It appears fairly clear, also, that 
the character and the number of different superimposed layers of 
peat overlying a land area are not determined by the nature of the 
mineral subsoil or its topography. The most tangible and readily 
recognized chemical change in undrained peat lands is seen in the 
marked deficiency of certain fertilizer constituents, in the progressive 
loss of oxygen from the plant tissues forming layers of peat, and in 
the reducing action of the water in various peat materials (6, p. 372). 
The conditions are quite different, however, when an area of peat 
has been drained, the surface layers are cleared and aerated, and de- 
composition of the organic matter sets in. Generally speaking, the 
solubility of mineral soils underneath peat areas is greater than that 
of the adjoining cropped and leached upland soils. The proportion in 
which the various mineral constituents are given up and accumulate 
in the rooting zone of crops is therefore highly important. Where 
these salts are dissolved in the soil moisture, the concentration of the 
solution may become excessively great in the course of time (pi. 2, 
B and C). The spots formed may prevent seeds from absorbing 
enough moisture to germinate, and they may injure the roots of 
plants growing at some distance from the place supplying the salts. 
It appears that the more disintegrated phases and finer textured 
types of peat are likely to show greater injury from dissolved salts and 
the adsorptive effects of organic colloids than the loose, fibrous layers 
of peat. Too much can not be said, therefore, about the desirability 
of studying carefully the mineral substratum as a limiting factor. 
