10 BULLETIN 1419, U. S. DEPARTMENT OF AGRICULTURE
peat. This can be practically solved through the protection afforded
to crops by shrubs or trees planted as windbreaks and shelter belts,
by crop rotations, by irrigation, or by proper cultural treatment of
the wind-swept muck soil.
Layers of woody peat (pl. 6 and digit 3 in the series of profiles in
pl. 1) consist partly of granular, well-disintegrated organic material
and partly of irregular-shaped woody fragments which have resisted
the decomposing action of air and microorganisms. Plate 6, A, shows
a profile section of an area of woody peat derived from a coniferous
swamp forest. The layer represents dark-brown, moderately well-
disintegrated granular material, as well as coarse woody fragments
from the stumps and roots of trees. The moisture content of the
underlying mineral soil was sufficiently low during the period of for-
mation to favor the growth of trees and a fair degree of decomposi-
tion of the plant remains. The ground-water level became elevated
in time, with the gradual accumulation of the peat material. Plate
6, B, shows a sample more or less typical of brown, laminated, poorly
decomposed, woody peat derived from shrubs. The lamination,
perhaps, is annual. Plate 6, C, represents a dark-brown, largely
disintegrated woody peat derived from a swamp forest. This air-
dry sample reveals a varying proportion of granular material and
woody fragments.
The growth of forest trees causes a greater humification of the peat
material containing the living roots, whieh in turn gives rise to the
formation of soluble organic and mineral substances. Because of
this varying rate of decay, a layer of woody peat may show a banded
or bedded appearance and a critical water content differing ac-
cordingly.
In the raw state all types of peat of whatever stage of previous
disintegration have a low value as nutritive constituents. When
surface peat soils are removed from a cultivated area, as in the case
of certain industries which dispose of peat for fertilizer purposes, the
exposed underlying brown and yellow-brown peat material is detri-
mental to crops, at least for a period. - Dwarfing of root systems and
cessation of plant growth appear to be partly due to the lack of sol-
uble nitrogen in the large supply of carbonaceous matter. Investi-
gations bearing on the nitrogen supply in peat materials have proved
that the content of organic nitrogen is not available for crops. In
the absence of any adequate balance between carbonaceous materials
and soluble nitrogen, deficiencies must be made up by manuring or
fertilizing. When properly aerated, cultivated, and mineralized, the
change from the peat stage to a material resembling humus mav take
place rapidly (pl. 5, A and D). oo
The fixation of atmospheric nitrogen by bacteria might be one of
several methods to measure the nutritive value of different types
of peat or of different stages of decomposition. It is doubtful, how-
ever, whether a layer of peat which has reached a mature stage of
disintegration in the field 1s in consequence more productive. Atten-
tion should be focused not so much upon the stage of decay but rather
upon the conditions, including the character of the layers below the
surface, which are antagonistic or associative in the continuance
of the soil-forming process. Field observations on the size and abun-
lance of trees present in undrained swamp forests may he cited here