Geoscience Reference
In-Depth Information
There is a lot of common ground with what scientists and engineers need to know
about soils and how to use the knowledge.
Peat land is gaining importance as potential land for agriculture due to its occur-
rence near coastal lowlands, which are usually developed and populated areas. In
recent years, extensive utilization of peat swamp areas has started due to the increas-
ing pressure on upland areas. However, from an agriculturalist's point of view,
peat soils have generally been recognized as a problem soil, with marginal agricul-
tural capability. Thus with it come a multitude of problems associated with such
development.
Drainage is a prerequisite for any agriculture development on peat. Essentially, it
removes the excess surface and subsurface water. However, drainage activities are the
greatest threat to the ecology of a tropical peat. By lowering the water table and
accelerating the rate of decomposition of the peat, drainage results in irreversible
changes in the hydrology, morphology and ecology of the peat land. The effect of
long-term drainage on peat soil morphology has been described in Chapter 6, whereby
drainage resulting in subsidence of 0.8m over 20 years resulted in the development of
a sapric-hemic-fibric profile.
As a result of drainage, the water table in the peat is lowered. The buoyancy of the
peat us reduced, which increases the overburden pressure, causing more consolidation
and subsidence. The subsidence compression again brings the surface level with the
water level.
Drainage and cultivation of peat soil increases soil aeration and reverses the carbon
flux into a net carbon dioxide (CO
2
) emission into the atmosphere. Cultivated peat
soils then become a large source of both carbon dioxide (CO
2
) and nitrous oxide (N
2
O)
emission. Thus agriculture development can contribute significantly to the increase in
atmospheric N
2
O (Melling and Hatano, 2003).
The original ecosystem will change radically and permanently because uncon-
trolled drainage bleeds the peat, the very medium that is the basis of its existence. There
will be more rapid runoff, higher peak flows and widespread incidence of flooding.
Over-drainage of peat land causes a chain of problems (Melling
et al.
, 1999). These
include subsidence, flooding, reduced water holding capacity, increased occurrence of
acid-sulphate soils, forest fires, pest infestation and termite attack, nutrient imbalance
and moisture stress to the crop (Andriesse, 1991). Excessive drainage of the peat will
also cause a transformation of its colloids, resulting in it having the properties of
irreversible drying.
The topo-hydrological characteristics of the peat also make water table control
in tropical peat development very complex. The complexity is even when the conver-
sion of these lands for agriculture is made in small individual pockets of about 5,000
hectares each within a peat basin and when there are crops with conflicting water table
requirements. The heterogeneous nature of tropical peat makes it difficult to do water
management. Designing an efficient water management system in peat land is made
more complex by the following factors:
•
Rainfall is not well distributed throughout the year
•
Spatial variation of rainfall
•
High variation in hydraulic conductivity or permeability
•
High fluctuation of the water table
