Environmental Engineering Reference
In-Depth Information
Usually, cover crops are planted by broadcasting seed or by hydro-seeding. Where seed
is in short supply, it may be sown in rows - in furrows located along the contours. In this
case, vegetation forms dense strips in the i rst year, spreading between the strips in subse-
quent years.
Where agricultural land use is planned, cereal grasses and legumes such as clover are
commonly used as cover crops. Where natural vegetation is to be re-established, local pio-
neer species are sought, particularly low, ground covering species with a scrambling or
sprawling habit. However, it is sometimes difi cult to i nd suitable species with plenty of
easily harvested seed, or for which the germination requirements are understood. In such
cases, introduced species are sometimes used.
The main requirements of a cover crop are:
Seed should be readily available;
Seed should germinate rapidly;
Species must be capable of growing in the prevailing climate and soil conditions;
Following germination, the plants should be capable of providing an extensive ground-
cover within the initial growing season;
Species used should not have the potential to become 'weeds';
Species used should not have the
potential to become 'weeds'.
Preferably, the plants should become established without the need for supplementary
watering.
Pioneer species are preferred because they are naturally suppressed as other species become
established by plant succession. Many are annuals and will continue to reproduce each year
until perennial species become established. Legumes are favoured because they add nitrogen.
The requirement to avoid establishing weeds does not relate solely to exotic species.
One of the most widespread plants in South East Asia is Imperata cylindrica , known in
Indonesia as alang alang . This species is easily established in disturbed areas where it rap-
idly achieves total coverage. However, it is allelopathic and therefore patently unsuitable
for use in mine land rehabilitation. Once established, it will preclude the establishment of
all other species. Not only should the species not be used but in many areas it is necessary
to prevent it from invading areas being reclaimed.
In contrast to alang alang , there are several perennial legumes that are commonly used
for mine land rehabilitation in Indonesia and elsewhere. A list of widely used legumes,
their main characteristics and requirements, is provided in Figure 21.2 . Commonly
used legumes in SE Asia are Centro ( Centrosema pubescens ), Bejuco ( Calopogenium caer-
aria ) and Puero ( Pueraria phaseoloides ), which are commonly combined in the same seed
mixture. Centro and Bejuca are both native to South America but have become natural-
ized in many parts of SE Asia, where they have been used for erosion control following
logging operations. Puero is native to East and SE Asia. All germinate rapidly follow-
ing rainfall and grow vigorously to form dense, leafy thickets totally covering the sur-
face in the i rst year if planted at relatively high rates (
4 kg/ha), or in the second year if
sown at lower rates. Centro has the additional advantage of being drought tolerant while
both Bejuco and Puero can tolerate acidic soils. Both Bejuco and Puero have a climbing,
twining habit, while Centro has a creeping, sprawling habit. Bejuco has the potential
to become a weed species in a grazing situation, because it is generally unpalatable.
However, in reclamation where forest is being established, all three species tend to dis-
appear over time as other herbs (particularly ferns), shrubs and trees become established
( Case 21.4 ). Apart from their use as groundcover for erosion control and nitrogen addition,
these plants are also suited to the provision of green manure, which is usually achieved by
ploughing to bury the foliage in the surface soil layer. This can help to build and improve
the topsoil layer.
 
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