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 yet 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 S. The 
burned-over area of peat land ( pi. 8, A ) 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 
peat 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. 
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- 
phuric acid, both of which are soluble in water and injurious to crops. 
In contact with calcareous waters or any form of lime these two sub- 
stances are changed into calcium sulphate (pi. 3, G). 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 
