Introduction |
In this series we start with some
of the issues regarding soil and water conservation followed by some new thoughts on
reading the landscape, which are not fully incorporated into the 'mainstream' thinking.
Are erosion and its causes correctly assessed? We end with the illustration of some
conservation techniques. |
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Narrative |
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Slide 1: Title
[taken by
Fahmuddin Agus] |
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Slide 2: How can this
landscape with fields laid out as a chessboard be kept in place on these very steep slopes
(>60 %) in Samarang, West Java? The intense cultivation of vegetable crops is severely
affected by sheet and rill erosion.
[taken by
Fahmuddin Agus] |
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Slide 3. Why bother
with soil conservation?
Soil conservation measures will not address all concerns such as loss of land productivity
(A), water quality (B) and water quantity (C) to the same degree. We have to differentiate
between them in evaluating environmental impacts of land-use and land cover change and in
considering options for maintenance of ‘forest functions' (as filter to
reduce soil loss, to maintain water quality and quantity) in agricultural
landscapes.
[taken by
Fahmuddin Agus] |
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Slide 4: A striking
example where things go wrong regarding land productivity, if the land itself is being
washed away in clean weeded coffee plantations (Sumberjaya, Lampung). The loss of land
productivity is mainly an on-site effect.
[taken by Bruno Verbist © ICRAF] |
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Slide 5: Effects on
water quality and water quantity are mainly felt downstream. Who or what is effected
downstream if rivers turn brown because of sediment load or if storm flow increase
dramatically. What upstream areas or ‘hot spots’ are contributing most to this
sediment load? |
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Slide 6: How easy is it
to keep the soil at its place and out of those rivers? Do we really need to put the land
back? |
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Slide 7: Erosion
is normally quantified as an amount of soil lost from a given area over a
specified period of time and is mostly expressed in ton per hectare per year,
as if net soil-loss is independent of the size of the measured area.
In the past the focus has often been on trying to keep the soil at its place only. Erosion
and its counterpart process of sedimentation can not be simply ‘scaled-up’ on an
area basis from observation plots to farms and watershed. |
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Slide 8: Most research
on soil erosion by surface runoff is mainly focused on a comparison of runoff and sediment
loss from plots with different land cover types (as treatments) with a bare fallow or
farmer practice as a control. The experimental plots usually have standard dimensions and
are normally protected from entering soil particle (run-on) from upslope. The difficulties
appear when it comes to scaling-up these results to what should be the target areas: farmers’
fields or catchment areas.
Like e.g. in this slide, it is relatively easy to quantify the erosion on the plots, but
the scaling up to the steep slope on the left side and the bushy vegetation in the valley
bottom is more trivial.
[taken by Meine van Noordwijk © ICRAF] |
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Slide 9: Most
agricultural landscapes have undergone a gradual process of intensification.
Here a schematic development of the landscape in a sub-watershed and its effects on storm
flow, net sediment loss and dry-season base flow: I. Original forest cover, II. Patches of
forest opened for shifting cultivation, III. Intensification of land use has brought most
land into cultivation, except for riverine borders and hedges along paths, IV. Reclamation
of all 'wastelands' has removed all filter strips causing a disproportional rise in net
sediment loss, V. Restored agroforestry landscape with permanently vegetated contour
strips and riparian woodlands.
[taken by Meine van Noordwijk © ICRAF] |
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Slide 10: Under which
category of the 5 above defined stages would you classify this landscape?
Sumberjaya, Lampung.
[taken by Bruno Verbist © ICRAF] |
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Slide 11: From a
distance such a slash-and-burn plot on a steep slope appears to be a serious erosion
hazard. However the water in the river is still clean! The filter zone between the source
of erosion and the river seems to be pretty effective.
[taken by Meine van Noordwijk © ICRAF] |
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Slide 12: To what
extent can a terraced irrigated rice field function as an effective filter?
[taken by Bruno Verbist © ICRAF] |
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Slide 13: A field like
this contains enough ‘surface roughness’ and ‘filter zones’ at the
foot of the slope to capture nearly all sediment, and pass on almost nothing to the
streams.
[taken by Meine van Noordwijk © ICRAF] |
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Slide 14: Where forests
are cleared for agriculture land will be exposed to sun and rain for some time, leading to
detachment and movement of soil particles (the picture shows an early stage of coffee in
Sumberjaya, Lampung, Indonesia). There is certainly erosion on the bare land, but where
does the sedimentation take place?
Conservation Measures
[taken by Bruno Verbist © ICRAF] |
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Slide 15: Grass strips,
shown in erosion prone vegetable-based farming, can have a strong filter function and lead
to formation of terraces. Especially for vegetable culture, where erosion often is a
problem, grass strips are an easy and cheap conservation measure, although it is not a
very common technique yet.
[taken by Umi Haryati] |
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Slide 16: Bench
terraces with stones supporting the steep walls require a lot of effort to construct. This
practice is found on areas where labour is not a problem, material is available on site
and the profits from the vegetables are high enough to justify all the efforts.
[taken by
Fahmuddin Agus] |
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Slide 17: Contour
-planting of leguminous shrubs can lead to terrace formation and improve soil fertility,
(see Tree-soil-Crop lecture note).
[taken by Sidik H. Tala’ohu] |
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Slide 18: Main
disadvantage of the hedgerows is the substantial amounts of labour required for pruning
and maintenance. The additional labour may not always be compensated enough by higher crop
yields.
[taken by Dennis Garrity © ICRAF] |
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Slide 19: Natural
vegetative strips with grasses and weeds are a low-labour alternative to tree-based
hedgerows. They are simple to install and maintain.
Natural terrace formation can be rapid, due to frequent tillage and water-induced soil
movement. Land preparation on the developed terraces becomes more convenient.
[taken by Dennis Garrity © ICRAF] |
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Slide 20: With a little
practice the 'cow's back method' can increase the speed of laying out contour lines
enormously compared to using the A-frame method. The farmer watches the cow's head in
relation to her tailbone. If the head is higher (than the tailbone), the cow is going
uphill, the farmer should steer down a little. If the tailbone is higher (than the head),
the cow is going downhill. The farmer should steer up a bit. An experienced farmer can
stay within the limit of 2% of the contour line, which is generally acceptable.
[taken by Dennis Garrity © ICRAF] |
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Slide 21: The natural
vegetative strips have been evolving into Eucalyptus agroforestry in
Claveria,
Philippines. The trees function as ‘bank’ and in many parts of the Philippines
the wood fetches a good price on the market.
[taken by
Fahmuddin Agus] |
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Slide 22: Combination
of Paraserianthes falcata and Gendarusa vulgaris (Tengklom in
Sundanese) to
stabilise terraces. Tengklom is very adaptable to low soil fertility and palatable to
ruminants. A plot nearby Garut, West-Java, Indonesia.
[
taken by
Fahmuddin Agus] |
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Slide 23: Vegetable
crop based farming in West-Java. Tree crops such as stink bean (Parkia speciosa),
jengkol (Pithecellobium jiringa), and kayu afrika (Maesopsis eminii) are
mostly confined to field borders and form a mosaic of landscape filter.
[
taken by
Fahmuddin Agus] |
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Slide 24:
Contour planting of tomatoes at the left. But it is clear that all farmers do not practice
this technique (yet), as you can see on the right side. Photo taken in
Claveria,
Philippines.
[
taken by
Fahmuddin Agus] |
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Slide 25: Sediment pits
between coffee trees in Sumber Jaya, Lampung. The pits improve the infiltration capacity
of the soil and are also used to collect tree litter to improve soil fertility. Annual
crops such as taro and cassava are often planted in the litter pits and provide an
additional income for farmers.
[
taken by
Fahmuddin Agus] |
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Slide 26: To what
extent has this landscape enough trees and are they well positioned enough to attain stage
V as illustrated in slide 9?
[taken by Bruno Verbist © ICRAF] |
AF
Models 
