20 BULLETIN 1419, U. S, DEPARTMENT OF AGRICULTURE
sible of measurement. The actual presence of organic acid is, how-
ever, considered to be less important than the injury due to mineral
acids and to lime deficiency. This condition may be remedied by
the careful use of finely ground lime. Determinations of acidity and
basicity have been included in systematic field work, partly because
convenient and fairly accurate methods are available for this pur-
pose.” The results, however, are still inconclusive, because the differ-
ent methods of determination give different indices of acidity. The
Azotobacter test might be decidedly preferable as regards the lime
requirement and the quantity of available salts, such as phosphates,
needed to render a layer of peat productive. Further work on this
subject is much to be desired.
Not only do reclaimed peat lands vary widely among themselves
in the fertilizer treatment required to make them profitable but also
the chemical composition of layers of peat under cultivation changes
continually. The methods of investigation are not vet sufficiently
delicate to follow these changes from peat to muck and humus.
Chemical and bacteriological tests should therefore be made over
a long period of years on peat lands with a specific profile.
Relative to the influence of the mineral substratum, the following
conditions should be taken into account in the selection of peat lands
for different uses. It is difficult to obtain satisfactory results on peat
lands with unfavorable topography of the adjacent land, steep slopes,
lack of outlet or fall, stony, gravelly, and quicksand subsoils, or hard-
pan underlying relatively shallow depths of peat. Excessive quantities
of soluble salts, sulphur, and iron contaminations give rise to spotty
areas, and even peat lands of considerable depth have only a limited
value under such conditions. Deep drainage and evaporation during
periods of hot, dry weather must be fully reckoned with as the influ.
ences that bring salts from the mineral substratum to the surface.
On the other hand, cool rainy seasons prevent a high concentration
of soluble salts, both by stopping excessive evaporation and by leach-
ing and distributing the mineral salts.
Typical injury caused by iron salts is shown in Plate 8. The
burned-over area of peat land (pl. 8, 4) contains solid mounds of iron
concretions in a locality where the ground waters and springs are
ferruginous. Plate 8, B, gives a closer view of the newly excavated
ditch, the drainage waters of which contain large quantities of iron
in solution. Upon exposure to the air the iron becomes insoluble
and precipitates. The cost of necessary labor and fertilizers and
of transporting and marketing make unprofitable the utilization of
eat lands with injurious subsoils. They should be recommended
for suspension or exclusion until a thorough and systematic search
for the presence of harmful substances in the mineral substratum has
been made. i }
How extensively iron sulphide in the form of marcasite occurs in
the underlying mineral soil of peat lands is not known. Nowhere,
however, does it threaten any injury except after drainage. Because
of oxidation by the air, marcasite forms ferrous sulphate and sul-
huric acid, both of which are soluble in water and injurious to crops.
bn contact with calcareous waters or any form of lime these two sub-
stances are changed into calcium sulphate (pl. 3, 0). Unproductive-
ness from this cause will not disappear until all the sulphide has been
neutralized by lime and any remaining pyrite has oxidized and leached