Introduction |
The spread of Imperata is
often linked to a loss of soil fertility, leading to reduced crop vigour. The Imperata
grass, which competes more effectively at lower fertility levels, gradually occupies an
increasingly large area. This is particularly true after forest or long fallow (bush)
clearance. Maintaining adequate soil nutrient status is thus one of the keys for
stabilising crop productivity and preventing Imperata encroachment. |
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Narrative |
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Slide 1: Title
[taken by K Hairiah © ICRAF] |
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Slide 2: …every
time you think you understand the constraints (left side of the onion) and identified a
possible solution (right side of the onion), there’s a new layer underneath. … all these layers are ‘real’, and should be part of
a solution; together they define ‘the issue’.
[taken by M van Noordwijk © ICRAF] |
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Slide 3. Forests have
been and continue to be opened for food crop production throughout S.E. Asia. Within a few
years a substantial part of these lands can (and has) become infested with the grass Imperata
cylindrica (‘alang-alang’, ‘cogon’, ….). Farmers may then
decide to move on and create new forest frontiers elsewhere, leaving the grasslands behind
as under-utilized resource. Four stages can schematically be distinguished: Stages A &
B can be characterised as ‘more people, less forest’, and stages C &
D as ‘more people, more trees’.
[taken by M van Noordwijk © ICRAF] |
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Slide 4: This land
looks green and fertile. It seems there is no obvious problem. Actually this is a massive Imperata
grassland in Pakuan Ratu, N. Lampung, which is often also called as "Padi
Lampung". The total area of Imperata grassland in tropical Asia is about
35 million ha, and the sum of conservative estimates for all countries is still about 21
million ha. With dwindling forest cover also the area of fertile soil (which is still
under forest cover) decreases, so there are no choices for farmers than rehabilitating the
Imperata grassland as agricultural land. In some parts in this slide, you can see
that some farmers have already started planting trees (e.g. rubber) or allowing some trees
(from the earlier forest) to grow back naturally.
[taken by K Hairiah © ICRAF] |
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Slide 5:
…….open the grassland (open land in the middle) for a food crop based system.
[taken by K Hairiah © ICRAF] |
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Slide 6: Under a high
input plantation system like sugarcane, usually the land is free of Imperata.
Normally the sugarcane is planted on flat lands or on the (moderate) slopes, while the
valley bottoms are covered by riverine or gallery forest. The white 'plumes'
of this 'overripe' sugarcane almost look like flowering Imperata.
[taken by K Hairiah © ICRAF] |
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Slide 7: Plantation
crops such as rubber or oil palm are particularly susceptible to Imperata at the
early stages of development because they do not develop a dense enough canopy to
adequately shade the weed. Imperata is not only an effective competitor for water
and nutrients, due to its extensive and often shallow root systems, but it also has
allellopathic effects on other plants.
[taken by K Hairiah © ICRAF] |
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Slide 8: Imperata
cylindrica is a perennial rhizomatous grass. Its propagates sexually by seed and
vegetatively by the extensive rhizome system. The underground rhizomes, which proliferate
in the soil, give rise to shoots with intervals of 25 to 50 cm. Rhizomes fragmented by
cultivation can also produce new shoots and rhizomes very rapidly. A 15-cm rhizome
fragment can produce more than 350 shoots in six weeks. The rhizome is sometimes used to
make herbal tea.
[taken by Anonymous] |
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Slide 9: The spreading
of Imperata is often linked to a loss of soil fertility, leading to reduced crop
vigour and more chances for the grass, which competes for light more effectively at lower
soil fertility levels. Therefore, maintaining adequate soil nutrient status is one of the
keys for stabilising crop productivity and preventing Imperata encroachment. Farmers experience in N. Lampung shows that continuous cropping of
cassava (usually 3-5 years after forest or bush conversions) leads to unfertile soil,
which is described in Bahasa Indonesia as " tanah kurus" or
"tanah panas" ( "thin soil" or "hot
soil"). Farmers also describe "white soil" as unfertile, as you can
see in this slide.
[taken by K Hairiah © ICRAF] |
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Slide 10: For many
rural families firewood is still the basic energy supplier. Large areas of sheet Imperata
prevent the growth of trees. This lady now has to walk miles in order to find
firewood! Notice the reddish brown colour of the Imperata in this slide due to
drought and also because it covered by dust!!!
[taken by K Hairiah © ICRAF] |
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Slide 11: Most fires
are set by people, either as a tool to clear land or as a weapon in attempt to settle land
(tenure) conflicts. So, during dry seasons Imperata grassland is often a 'hot spot'
of fire hazards! Imperata can survive fire, because it has many growing points on
rhizomes below a soil depth of 5 cm, and fire does not increase soil temperature above a
critical level below this depth.
[taken by M van Noordwijk © ICRAF] |
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Slide 12: Oil palm
trees with an undergrowth of Imperata have a high risk of fire damage. Damage due
to fire can be survived, but will negatively affect the yield. According to farmer
experience in N. Lampung, oil palm is slightly more fire resistant than rubber.
[taken by M van Noordwijk © ICRAF] |
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Slide 13: Imperata can
thus regrow quickly after a fire event and it tends to flower and produce seed within 2
months after being burnt. Many other plants and trees are not so well adapted to fire and
will be killed or will recover much slower. The leguminous tree Peltophorum was
found to be resistant to fire as well, as it resprouted quickly after being burnt. The
species is potentially useful for controlling Imperata.
[taken by M van Noordwijk © ICRAF] |
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Slide 14: Fire
stimulates resprouting of young shoots of Imperata, which are more digestible for
grazing cattle than the old shoots. Although it must be mentioned that Imperata is
a rather poor fodder compared to many other grass species.
[taken by M van Noordwijk © ICRAF] |
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Slide 15: Imperata produces
annually a shoot biomass of about 3-5 Mg ha-1. It can be used as mulch or as
thatch.
[taken by K Hairiah © ICRAF] |
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Slide 16: House roofing
made of Imperata biomass keeps the house cool, although it has a high risk of fire
and requires a lot of labour to maintain it. |
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Slide 17: This bare
soil area is heavily eroded, in contrast to the nearby land, which is protected by a dense
Imperata cover.
[taken by K Hairiah © ICRAF] |
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Slide 18: The most convincing reason to rehabilitate Imperata
grassland is to make the land more economically productive. In this slide the
farmer is enriching the established hedgerows with fruit tree species he desires like
mango, Zapota, Parkia.
[taken by M van Noordwijk © ICRAF] |
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Slide 19: Imperata grassland
rehabilitation can succeed only when four critical conditions are met!!!
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Clear and secure tree or land tenure |
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Effective local community fire prevention and control |
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Technical know-how of shade based control and soil fertility
improvement |
| Market access, both physically and economically |
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Slide 20: There are
many farmer practices to control Imperata. The methods chosen depend on the
resources available (mainly labour) and access to credit for the farmer.
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If labour is cheap and available for poorer farmers, hoeing
is recommended. |
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If labour would have to be paid for, it is mostly used for
planting food crops such as upland rice, maize or soybean. Spraying herbicide is
also commonly used by farmers due to shortage of labour. |
| [taken by K Hairiah © ICRAF] |
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Slide 21: Within Imperata
grasslands, trees and shrubs (e.g. Peltophorum and Dillenia) may
continue to grow and once the canopy is dense enough or closed, it will shade-out Imperata.
[taken by K Hairiah © ICRAF] |
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Slide 22: Basically two
approaches are used by the farmers for initial clearance of Imperata fallow:
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no-till techniques based on systemic herbicide (e.g.
glyphosate), applied on young regrowth after burning existing biomass or slashing and
removing it, |
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soil tillage a) by hoeing (manual) or b) ploughing (using
animal or tractor power), usually after the Imperata aboveground biomass was burnt
to make the work easier. |
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Slide 23: Biological
control methods for Imperata are mostly based on providing shade. This slide shows
a field experiment in N. Lampung – Indonesia, using Gliricidia as a hedgerow. Gliricidia
has a not so dense canopy, which makes it less effective for controlling Imperata.
[taken by M van Noordwijk © ICRAF] |
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Slide 24:
Peltophorum has a denser canopy than Gliricidia, so it is more effective for
controlling Imperata. For research purposes Peltophorum was established in
lines in an Imperata field as a first step toward a rotational hedgerow
intercropping system. It must be mentioned that it is unlikely that farmers will adopt
this labour intensive technique.
[taken by M van Noordwijk © ICRAF] |
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Slide 25: To answer
this question the light intensity reduction by trees and the amount of Imperata was
measured and an experiment using artificial shading on Imperata field was set up. This slide shows the measurement of light interception by trees (Gliricidia
and Peltophorum) compared to an open area (without trees) at the same experimental
site as shown in the two former slides.
[taken by M van Noordwijk © ICRAF] |
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Slide 26: This
shade-intensity experiment was carried out to quantify the response of well-established Imperata
to shade with a controlled, known light intensity reduction and different duration.
Artificial shade (nets) were used. The treatments were:
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0 % shade = full sunlight |
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55 % shade = 45 % sunlight |
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75 % shade = 25 % sunlight |
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88 % shade = 12 % sunlight |
| The decline of standing Imperata biomass over time
and the regrowth ability from rhizomes were quantified by weighing the biomass, which was
removed on a monthly basis. |
| [taken by K Hairiah © ICRAF] |
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Slide 27: The
artificial shade-intensity experiment showed that even if light levels were reduced to
about 10% of full sunlight, an established Imperata stand would only gradually
decline. A 50 % shade reduction for up to 8 months had little effect on the Imperata (re-)
growth. |
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Slide 28: Re-growth after
removing all Imperata aboveground biomass was more affected by shading
than was the standing biomass. A 55% shade treatment, that would be considered problematic
for most food crops, had no effect on the ability of Imperata rhizomes to
re-sprout. Only when an 88% shade was applied for more than two months, did the ability of
rhizomes to re-sprout decline to a negligible amount. |
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Slide 29: The various
tree and plantation crops differ in age and tree basal area. Light intensity reduces more
quickly for a given stem basal area in rubber and Acacia mangium systems than in a
pepper agroforestry system (using Gliricidia sepium and other trees as support and
shade trees) or under Paraserianthes falcataria. |
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Slide 30: The results
of the artificial shade experiment was then compared with results of the survey of Imperata
occurrence versus light intensity under a range of agroforestry systems. Imperata biomass
decreased drastically when relative light intensity was reduced to 20 %. This suggests
that farmers were weeding the Imperata, as we learnt from the artificial shade
experiment that shade has much more effect on the regrowth (after slashing and removing
the Imperata) than on the standing biomass. When more than 20% of sunlight still
reaches the ground, Imperata still has a chance in these agroforestry systems. |
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Slide 31: Artificial
shading experiments and on-farm surveys showed similar results with regard to the
requirement for light interception to control Imperata. To control Imperata, light
intensity at ground level needs to be reduced to < 20%, for at least 2 months after
slashing of standing biomass. |
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Slide 32: Farmers in N.
Lampung, Indonesia got interested in planting timber trees such as teak, mahogany, Paraserianthes
etc. on their Imperata grassland. Many farmers noticed, however, that teak and Imperata
litter will be easily subject to fire during the dry season as they are very slow to
decompose. Farmers will explore a range of options
for Imperata reclamation when some conditions can match their expectations such as
security of tenure and village level rules on use and control of fire.
[(left) taken by K Hairiah © ICRAF]; [(right)
taken by J Roshetko © ICRAF] |
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Slide 33: … and
high enough benefits and/or profits from firewood or timber.
[taken by K Hairiah © ICRAF] |
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