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. |
|
|
|
Narrative |
|
 |
Slide 1: Title, with an
example of a mixed garden in Lampung, Indonesia. Possible questions to the audience:
1. What crops can you identify? (answer: coconut, cassava, cacao, …)
2. What kind of interactions do you think are there between those various annual and
perennial crops? (answer: shading, water and nutrient competition, litter fall, nutrient
pump, interactions via pests and diseases, …)
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 2: Sketch of
possible tree - soil - crop interactions
In simultaneous agroforestry systems, trees and food crops interact in many ways, leading
to positive and negative impacts on the growth of both trees and crops. Schematic drawing
of tree crop interaction:
| » |
Negative
effect (or competition): a = shading; b= root competition for water and nutrient; |
| » |
Positive
effect (or complementarity): c = litter fall and pruning biomass of trees increase C, N, P
and other nutrients; d = deep rooted trees play a role as ‘safety-net’ for
leached nutrients in the deeper layer or as ‘nutrient-pump’ for fertile soil.
Trees reduce weeds (through shading in relevant periods of the year) and thus reduce the
risk of dry-season fires. |
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.]
|
|
 |
Slide 3. Shading.
An example of hedgerow intercropping with maize between hedges of Peltophorum and Gliricidia,(both
hedges were pruned at the same time!). The distance between hedgerow trees is 4 m.
Pruning is generally done whenever the tree canopy gives too much shade to the crop. You
notice that Gliricidia has a wider canopy than Peltophorum and thus gives
more shading to the intercropped maize. Consequently more pruning has to be done to reduce
light competition. Peltophorum has a dense canopy concentrated near the trunk,
which gives a high mulch-to-shade ratio.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 4: Root
competition.
A shallow tree root system leads to a strong competition with annual crops in the upper
soil layer for nutrients and water. A "quick and dirty" method by digging up and
removing soil around the tree root system makes clear how the root system has actually
developed and gives an indication regarding potential root competition. This slide shows
the shallow tree root system of Ceiba pentandra (left) and Leucaena (right).
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 5: Root
architecture.
For tree species that normally have a deep root system, a shallow root system is usually
the initial symptom of Al-toxicity on acid soils. The root system of this rubber tree on
acid soil is distributed quite well horizontally and vertically. It indicates that rubber
trees have a high tolerance on Al-toxicity. On fertile soils a deep root system can
operate as a 'nutrient pump'. In infertile soil it can act as 'safety net' slowing down
leaching.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 6: Mulch.
A hedgerow intercropping system during dry season. Soil moisture is retained by the mulch
of the plant residues and the tree canopy. The litter of the plant residues functions as a
'bank' of nutrients.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 7: Reducing
weeds.
Peltophorum has a dense canopy concentrated near the trunk, which - as mentioned
before - gives a high mulch-to-shade ratio. When left unpruned during the dry season the
hedgerows provide (dense!) shade which controls evaporation and the development of
unwanted Imperata grass. When the growing season starts, pruning is needed. The
bigger branches (diameter > 2 cm) can be used for fuelwood.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 8: Canopy
shape and reducing weeds.
Trees have an important continuous impact on the amount of weeds (as e.g. Imperata)
and reduce fire risk in the dry-season, because of a permanent green cover. Here we
see a dry season view of Peltophorum planted in lines. |
 |
Slide 9: Low
quality of litter fall.
Litterfall -here under Peltophorum - can shade out weeds, maintain soil organic
matter and soil moisture. Low quality litter decomposes slowly and will give a good soil
cover in a longer run. Litter can be quantified by collecting what fell on the surface
using the quadrant method. Hereby litter is regularly collected and weighed per quadrant.
From this it can be calculated how high litter production is per unit area.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 10: Black
soil is fertile soil!
A slowly decomposing organic layer can maintain a good soil structure. This slide shows
the rich organic top layer under forest. It has a darker colour and a porous structure to
allow more water infiltrate into soil. Soil under agriculture practices shows a lighter
colour and is more compact.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 11: Tree root system
can act as nutrient pump and improve root distribution of subsequent crops
A deep tree root system, as shown by this Leucaena tree can act as a
nutrient-pump on weathered rock in the deeper layer of fertile soil (left). A deep tree
root system can also improve the development of the root system of subsequent crops. The
right slide shows how decayed tree roots in acid subsoil in Nigeria created a 'channel'
for maize roots to grow deeper into the subsoil.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 12: Tree root
system as a ‘safety-net’ of leached nutrients in deeper layer
A deeper root system of trees in hedgerow cropping systems is very useful for nutrient
recycling. Nutrients, leached to deeper layers during the crop growing season will be
absorbed by the roots of hedgerow trees. Later, those nutrients will be released on the
soil surface through litter. The tree root system, which grows underneath a shallow maize
roots system then acts as a ‘safety net’ for nutrients. A shallow root system of
Leucaena can not be a safety-net for leached nutrients, but in contrast may compete
(for water and nutrients) with maize roots. |
 |
Slide 13: Is Jack fruit a
drought tolerant tree?
Crop growth on acid soil is often limited by Al-toxicity, and the indicator of an
Al-tolerance plant is shown by a well distributed root system in the deeper layer. Jack
fruit has a deep root system on acid soil and will in consequence be more tolerant to
drought. In this plot jackfruit grows mixed with other crops as banana, durian, Pithecellobium
(jengkol), Psidium guajava (guava) etc.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 14: How to
quantify the interaction?
How can the positive and negative interactions in the agroforestry systems be
separated? It is very complex as both interactions happen at the same time.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 15: Experimental
treatments.
To discriminate between positive and negative interactions a research experiment was set
up to isolate and quantify the various parameters.
How this was done for each parameter is explained in the following slides.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
|
Slide 16: How
to test shading effect?
The first half row of a hedgerow was pruned and the other half not. The difference in crop
production between those treatments can be interpreted as shading effect of trees.
[taken by Fahmuddin Agus] |
 |
Slide 17: How
to test root competition.
To estimate the competition for water and nutrients, treatments need to have crops and
trees mixed, with following treatments:
| a. |
Without root barrier |
| b. |
With root barrier. A ditch is made at
50 cm from trees, a plastic sheet is installed on a soil profile wall in "Z"
shape to avoid roots growing underneath. |
|
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
|
 |
Slide 18: How
to test mulch effect?
Mulch from the prunings of trees shades out weeds and maintains soil moisture.
To test the mulch effect the treatments are:
| a. |
without
mulch transfer |
| b. |
with mulch transfer at different level |
|
|
| Before Calliandra biomass
was transferred to neighbouring plots, the biomass of the prunings was quantified. The
woody branches (diameter >2cm) were used as fuelwood outside the plot. Leaves, twigs
and young branches were returned to soil in the neighbouring plot. |
| [taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
|
 |
Slide 19: Biomass
transfer.
The prunings were transferred to neighbouring plots without trees. The arrow in the left
hand side (1X) points to a plot which got 9 Mg ha-1 biomass(you can see a few
empty spots). On the right hand side is plot which got the double amount: 18 Mg ha-1.
Possible question to the audience: Why do we apply 2 levels of biomass?
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 20: Biomass
transfer.
Darker soil is an indicator that more organic matter was added.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 21: Long
term residual effect.
After 8 years the hedgerow trees were removed in part of the plots. All of old
trunks were weighted to estimate the amount of nutrients exported out of plot. After tree
removal the maize was planted.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 22: Control
treatment.
The control treatment was maize monocropping without hedgerow trees. Each plot in the
control treatment was split into four subplots to test the response to various levels of
N-fertilisation.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 23: Results of
the test for long term residual effect.
Maize yields showed a strong response in the first and second season after tree
removal, based on soil fertility maintenance ('residual effect'), compared to the
continuously cropped control plot. In the plots where Calliandra (C) and Leucaena
(L) had grown, maize yields (average of two seasons) were significantly higher than those
obtained with the highest N-fertiliser rate tested (135 kg ha-1), showing a
major below-ground residual effect of the N-fixing trees just removed.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 24:
Results of the tree – crop – interaction experiment
Under the "normal" hedgerow intercropping system, however, Peltophorum
gave maize yields higher than those obtained in the control plot with N-application of 90
kg ha-1. The difference was largely due to above-ground interactions (little
shade), as the effects of fresh mulch application and below-ground interaction (measured
by the effects of root trenches) were small. The relative success of the local tree Peltophorum
in this experiment was not due to very pronounced positive effects, but to small
negative effects. This species is less competitive than the others, partly because
of a deeper root system, (which is why it was selected initially), but especially
because of the shape of its canopy (concentrated near the tree trunk, see former
slides (3, 6 and 7)), which gives it a high mulch-to-shade ratio.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 25: Mulch
effect on maize yield
Mulch transfer of either single (9 Mg ha-1) or double mulch rates (18 Mg ha-1)
in the second season (which was much drier than normal) produced positive effects, clearly
outyielding the N-response. As all treatments received a moderate basal P fertiliser
dressing (since low P availability is the main limiting factors of crop growth), we
attributed the mulch effect largely to positive effects of improved water status as a
result of reduced evaporation from the soil.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 26: Decline of
residual effect 2 years after tree removal
Removal of hedgerow trees improved maize growth because there was no competition of
light and there was an increase in nutrient availability from the mineralisation of soil
organic matter.
Two years after tree removal, this positive residual effect seems to be no more
effective due to Al toxicity which is the main limiting plant growth on acid soil. In the
front part A, you see maize in the fifth cropping season after Gliricidia trees
were removed. Notice the yellowish and smaller maize compared to the one in the back (B,
with the small trees). Maize in part A suffered more to Al-toxicity due to lack of organic
material input, while part B still get biomass through continuous tree pruning. Biomass
input reduces Al-toxicity because the organic-acids released during decomposition and
mineralisation bind and fix Al. The reduction of Al increased the concentration of
available P in the soil solution and improved maize growth.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
 |
Slide 27: Conclusion
Overall the experiment shows the considerable positive
soil fertility effects that can be obtained with tree mulches on these acid soils, but it
also points at the strong competition that occurs in hedgerow intercropping. Agroforestry
systems are only beneficiary from a biophysical point of view, if there is at least some
complementarity in resource capture.
[taken by Meine van Noordwijk and Kurniatun Hairiah from the BMSF Project, North-Lampung,
Indonesia.] |
AF
Models 
