Present - Danish Water Forum

Low-cost soil- & water-conservation
with many early benefits
(’Climate change increases incidents of extreme rainfall’ in on-line programme, oral and poster
presentation)
By Torsten Mandal,
agronomist, independent consultant, external PhD student.
Acknowledgement:
-N E Nielsen, Lab. Soil Fertility & Plant Nutrition, Inst. Agric. Sci.,Faculty Life Science, Univ.
Copenhagen
-D Nyamai, Kenya Forestry Research Inst.
-Danida and other sponsors.
Contact:
TorstenMandal@gmail.com
Google: “Torsten Mandal” IOP or XPS for articles
A) OBJECTIVE: Briefly, more sustainable, cost-effective methods are increasingly
needed for reducing sudden surface water-runoff and drought damages while improving
food- and feed-security. Nitrogen-fixing multipurpose trees related to beans (legumes) are
needed in large numbers; but new solutions to establishment and management problems
were badly needed. Recycling of ash from kitchen-firewood to nitrogen fixing trees was
one of the solutions.
Global warming increased extreme rainfall events (and drought) even more than
previously thought and modelled (Allan and Soden 2008, Sugiyama et al. 2010). Rapid,
superficial, water-runoff leads to erosion, landslides, sedimentation, water pollution, formation
of mosquito-pits, and lack of drinkable water, etc. Preventing runoff is more cost-effective,
than treating damages but is often neglected by urban-based decision-makers.
Sustainable adoption of soil and water conservation requires early benefits to landusers
as well as low establishment and maintenance costs. The major cost for a popular
method, e.g. in central Kenya, Rwanda and SW Uganda, is watered, transplanted, nitrogenfixing
tree seedlings, particularly of calliandra (Calliandra calothyrsus). More reliable direct
seeding methods were needed giving early benefits.
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FIGURE 1. Calliandra hedge direct seeded with improved methods by small scale farmer.
Such tree species can protect the soil surface by providing low cover, stabilize soil
aggregates and terraces, improve water infiltration, add nitrogen to fodder grass lines, and
provide good firewood and dry-season feed-supplement. The direct soil conservation effects of
such tree-legume hedges are important but with much variation and much room for
improvement (e.g. Nkonya 2008, Young 1997). Improved low-input establishment of fodder
hedges by direct seeding as suggested by Mandal and Nielsen (2004) is also needed to prevent
overgrazing causing erosion and run-off (Thomsen et al. 2007).
Dry periods and heat are major challenges, for both transplanted and direct seeded trees, and
require enough coarse roots (>2mm) that can transport water up from deep moist soil through
dry soil (e.g. pers. obs.). Effects of phosphorus (P) application on root growth needed studies,
and so did wood-ash as a source of P. To prevent landslides, numerous hedges with much
coarse roots and short light tops are needed. Accordingly, new options for direct field
seeding of calliandra were studied to ensure a rapid, early growth in poor soils, despite
unpredictable climate. So are more appropriate options for managing contour hedges for
soil and water conservation compatible with producing firewood, feed and crops (Mandal
and Nielsen 2002; Mandal and Nielsen 2004; Mandal (unpublished).
B) METHODS: The data were obtained with calliandra from various replicated researchmanaged
trials in farmers’ fields at the humid and mainly subhumid zones, having two annual
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ainy seasons, in Western Kenya near Maseno research centre near the equator at about 1400 m
altitude. The wood ash experiment was with only 1 m distance between hedges (as used with
improved fallows) and 0.1 m within row. The wood ash (1.3% phosphorus =P) was mixed
well into 20 cm wide bands and 10 cm deep (normal hoeing) placed 5-15 cm below seeds.
FIGURE 2.
FIGURE 2. Calliandra seeds were scratched to ensure water uptake and avoiding risky
hot water pre-treatments and soil enriched with kitchen wood ash and nitrogen fixing
bacteria.
Farmer participation and laboratory studies were also used to develop and check the solutions.
Hedge-management and soil-and-water-conservation effects were mainly studied by
observation studies. See Mandal and Nielsen (2002, 2004) and below for details.
C) RESULTS:
Low-input solutions were comparable to the best conventional solutions, and key results
were at least twice as good as with no treatment control, and were statistically significantly
better. Improvements included:
1) After only 14 days, 87% field germination was achieved by scratching the waterproof
seed-surface with a sandal against a rough concrete floor (no watering, Mandal and Nielsen
2004). Without effective seed pretreatment, it took 7 weeks to get 50% germination, often too
late to survive weeds, the dry season starting 4 month later, and cultivation. Soaking mature,
dry, undamaged calliandra or Sesbania sesban seeds in unheated water 3 days, as recently
recommended to farmers, did not induce any visible water uptake in any of 20 seeds because
they were dry, mature and undamaged (unpublished), No Leucaena leucocephala seeds took up
water after 35 days in unheated water (e.g. Mandal 1994).
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Field germination, %
2) Germination of the small weed seeds during a dry spell was significantly decreased to less
than the half by leaving the 5-cm soil-surface loose above the bigger calliandra seeds so water
could not be sucked up to the weeds by soil (Mandal and Nielsen 2002). Most farmers were
not aware of the fact that firming seed below desired seeds (or seedlings) increased tolerance to
drought.
3) Good root-nodulation (by transferring 10 g colonised soil, or a soil-incubated nodule m -1
hedge (7 days locally and then crushed) for atmospheric nitrogen fixation when needed (Mandal
and Nielsen 2004).
4) Fair germination of calliandra in continuously continuous direct sun was achieved by
removal of hot soil 5 to 7
days after seeding from a 70
ridge above germinating
seeds else germination
failed,
60
FIGURE 3:
Hot sun all
day
50
Light shade
FIGURE 3.
Germination during dry
sunny period of
Calliandra calothyrsus.
40
30
20
5) About 2 to 3.5 times
higher dry matter
production was obtained at
13 to 30 weeks after direct
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seeding (by mixing about
1% kitchen wood ash well
into the nitrogen- and 0
phosphorus-deficient soil at
Controle Removed
20 cm width by 10 cm
Removal of hot soil surface
depth (from 5 to 15 cm
below the seed to prevent
scorching).
Low phosphorus (=P) mobility and plant uptake are big problems for nitrogen fixing plants
in tropical soils, particularly for young plants and during droughts. Moderate ash dose
significantly increased P-uptake as much as economically optimal doses of P fertilizer 13
weeks after direct seeding of calliandra tree-legumes on N and P deficient soil. FIGURE 4:
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P above ground, kg/ha
1
0.8
Wood-ash
TSP
0.6
0.4
0.2
0
0 60 120 180
kg phoshorus (P) / hectare
FIGURE 4. Phosphorus uptake 13 weeks after seeding calliandra supplied with kitchen
wood ash or triple super phosphate.
Aboveground biomass was also strongly increased by moderate wood ash doses even 30
weeks after direct seeding (FIGURE 5 a, below).
The best dose for early root and top growth after only (13 to 25 weeks after direct seeding,
150 g/m ash, 20 kg P/ha), also increased 30 weeks root growth including coarse roots in the
enriched zone strongly, but not high ash doses (FIGURE 6 b). Other root-results varied much.
Fresh ash is very alkaline (pH 11 to 13) and with high content of soluble salts. Deep root
growth in acid subsoil can be improved by liming (e.g. with kitchen wood ash) and by better top
growth.
Accordingly, leaflet-pairs for the 20-dose were at least as open as for controls early in the
dry season indicating good water uptake (FIGURE 6 c):
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Leaves+stem dry
weight, kg/ha
Coarse root d.w.,
enriched zone, kg/ha
Leaflet opening,
degree
10000
9000
8000
7000
6000
5000
4000
3000
2000
1500
a
0 20 40 60 80 100 120 140 160 180
b
kg phosphorus (P) /hectare
1300
1100
900
700
500
c
90
wood-ash
TSP
80
70
0 60 120 180
kg P / hectare
FIGURE 5 a b c. Effects of wood ash or triple super phosphate.
Accordingly, at the start of the dry season, 30 weeks after direct seeding (not before), rootnodulation
was several times higher when 20 to 60 kg P hectare -1 was applied as wood ash
rather than TSP. It also indicates good potential for nitrogen fixation and growth at dry times.
More drought tolerant and nutrient demanding species can also be chosen like suitable
proveniences of Leucaena trichandra or Sesbania species.
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Weeds, g
6) Competition for water etc. with faster growing weeds is a problem with standard methods.
In the mentioned ash experiment only high P-fertilizer doses to calliandra increased the critical
early weed and calliandra growth much, increased shade on the hot soil surface can have
contributed, FIGURE 6:
45
FIGURE
6. Early weed
growth with wood
ash or rapidly
soluble phosphate
near hedge.
40
35
30
25
wood-ash
TSP
In a separate
experiment, early
weed growth was
not increased by
wood-ash. In
contrast, it was
increased much by
rapidly water
soluble P-fertilizer
(TSP), particularly
when combined
20
15
10
5
0
0 20 40 60 80 100 120 140 160 180
kg phoshorus (P) / hectare (ha)
with N-fertilizer (Mandal and Nielsen 2002). Local cow-manure also increased weed growth
much in another (unpublished). Slow weed growth reduce risk of damage to hedges by
weeding by workers close to seedlings and to soil/water-conservation effects.
Further, maintenance of water conservation structures was much easier under the
young hedges growing well. In farmer’s fields, terrace formation was by sedimentation was
impressive when cultivation was not too close, and distance between trees 10 cm rather than
the usual 30 cm. Stable edges of 30 cm could be seen about five years after establishment in a
field with slight slope. This confirms the need of effective direct seeding methods. Farmers’
often used new hedge management methods when introduced to them.
Formation of wood and seeds as well as preservation of feed, green manure and near-ground
protective soil cover is a challenge when only cutting is advised. In observation studies,
farmers found the following three new options we developed useful to delay cutting of stems
grown in rainy seasons between crops:
A) Partial breaking over a knee of 0.5 to 3 cm thick stems,
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B) Stripping off composite leaves with a forked branch sparring the tip, stem and the cover
near the ground, and/or
C) Bending and twisting stems together.
FIGURE 7.
FIGURE 7. Young calliandra stem stripped with forked branch.
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FIGURE 8.a. Lowest calliandra branch stripped with forked branch.
These methods prevent much shading in cropping seasons, make protecting ground-near soilcover
possible at the start of the rainy seasons, and allow time to develop wood that is more
useful, seeds, dry season feed and nectar.
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Direct field seeding can be done on flat ridges, and short water conservation furrows can be
constructed above the contour line during establishment, below them later. Soil around mature
stems was tolerated, and it can increase water conservation and tolerance to fire. Weeding
under hedges can be minimized if kitchen wood ash is used instead of fertilizer or manure.
Finally, the only 10-cm in-line distance between shrubs possible can be used to trap litter and
increase water infiltration.
Direct seeded calliandra can also grow on degraded grassland, or on stony hills where it can
hold back run-off water, soil, organic matter and seeds from other species so some of them grow
spontaneously, e.g. Senna spectabilis providing termite resistant wood needed for crop stores
improving ability to cope with unpredictable climate (FIGUR 9).
FIGURE 9. Stony hill-top re-vegetated by useful direct seeded tree-legumes.
D) CONCLUSIONS: Improved low-input methods can contribute to better soil and water
conservation, increase wood growth, and supply soil with nitrogen-rich organic matter and
provide drought tolerant feed supplement. The methods are attractive, reliable and
sustainable for e.g. small-scale farmers in an unpredictable tropical climate. This can reduce
many important climate-related problems (heat, drought, flooding, erosion and CO 2 -emission).
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E) ACKNOWLEDGEMENT: Danida for research grant, various funds for support, late
Professor N E Nielsen, Faculty of Life Science, University of Copenhagen and Dr. D Nyamai
(then Head of Agroforestry Division Kenya Forestry Research Inst., now at World Agroforestry
Centre) for supervision. Present PhD supervisors Professor J K Schjørring and Dr. A de
Neergaard. The collaboration with CARE Denmark+Rwanda, ICRAF, and Vi Agroforestry
(Tanzania and Kenya as consultant), at various stages between 1990 to 2009 is also appreciated.
F) REFERENCES:
Allan R P and Soden B J 2008: Atmospheric warming and the amplification of precipitation
extremes. Science 321, 1481 – 1484.
Thomsen N, Nielsen M O, Hansen J, Henriksen J, Madsen J, Jensen H A, Mandal T, 2007.
Give a goat - assessment project 2007 Danish Church Aid, Copenhagen, Denmark.
Mandal T 1994 Pre-treatment of hard coated seeds of leguminous shrubs. In: The 4 th
International Symposium. Windbreaks and Agroforestry. July 26-30 1993,
Hedeselskabet, Viborg, Denmark, pp. 233-236.
Mandal T and Nielsen NE 2002: Direct seeding of multipurpose tree-legume hedges using an
improved method. In: Ramalho-Filho A et al (eds) Proceedings of the Third
International Conference on Land Degradation and Meeting of the IUSS
Subcommission C - Soil and Water Conservation. Rio de Janeiro, September 17-21,
2001. Rio de Janeiro, Embrapa Solos.
Mandal T and Nielsen N E 2004 An improved low-input method for establishing calliandra
hedgerows on small-scale farms in western Kenya. Agroforestry Systems 60: 227-231.
Nkonya E, Gicheru P, Woelcke J, Okoba B, Kilambya D, Gachimbi L N 2008: On-Site and offsite
long-term economic impacts of soil fertility management practices. The case of
maize-based cropping systems in Kenya. IFPRI Discussion Paper 00778. Environment
and Production Technology Division. Int. Food Policy Res. Inst.
www.ifpri.org/pubs/dp/ifpridp00778.pdf.
Sugiyama M Shiogama H Emori S 2010 Precipitation extreme changes exceeding moisture
content increases in MIROC and IPCC climate models Proceedings of the National
Academy of Science of the United States of America 107, 571-575.
www.pnas.org/cgi/doi/10.1073/pnas.0903186107.
Thomsen N, Nielsen M O, Hansen J, Henriksen J, Madsen J, Jensen H A, Mandal T, 2007.
Give a goat - assessment project 2007 Danish Church Aid, Copenhagen, Denmark. Free
PDF.
Young A 1997: Agroforestry for Soil Management 2 nd ed. ICRAF and CAB Int. 320 pp.
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