Agriculture Reference
In-Depth Information
Ofw
Layer of standing water occupied by
micro and macro-fauna and -flora
Oxic floodwater soil interface, a few
mm to a few cm thick depending on
floodwater aeration, soil reducing
conditions, mixing by soil animals
and percolation
Apox
0
10
Apg
Anoxic soil layer in which pe + pH is
below the range at which Fe(III) is
reduced, except in the rhizosphere
20
B
Subsoil properties vary with the type
of water saturation. In aquic
moisture regimes the whole horizon
is largely reduced throughout; in
epiaquic regimes, where the water
table is perched, the horizon
generally remains oxic and is
mottled along wide pores
30
40
Figure 1.3 Schematic profile of a submerged soil with redoximorphic features
is more intermittent, there may be more-distinct layers in the soil with differ-
ent redoximorphic features. The transition between these soil types in partially
drained wetlands may occur in a matter of decades.
At the boundary between uplands and wetlands there is, in some circum-
stances, an interaction between organic matter accumulation in sediments and the
development of wetland conditions. Some level of organic matter accumulation
is required to drive anaerobic metabolism. But also, because, in general, well-
decomposed organic matter improves the water holding capacity of mineral
soils, particularly in medium to coarse textured sediments, and particularly if
the clay mineralogy is dominated by low activity kaolinitic clays, there is a
feedback between organic matter accumulation and the extent and duration of
water saturation.
Particular modifications of these patterns occur in wetland rice soils. Repeated
working of the soil for rice often results in permanent changes that mask the
soil's original character. Gross changes are caused by levelling, terracing and
puddling the soil for rice, which destroys the soil structure. Over time a 'traffic'
pan of compacted soil often develops, 5-10 cm thick at 10-40 cm depth. This
has a greater bulk density and is less permeable than the overlying surface soil,
Search WWH ::




Custom Search