Mr Shuichi Oyama, Kyoto University, Japan. Global Symposium on Soil Erosion (GSER19), 15 - 17 May 2019 at FAO HQ.

1. From Soil Erosion to Soil Accumulation: Recycling
Urban Organic Waste to the Eroded Land in Sahel,
West Africa
Shuichi Oyama
(Kyoto University)
Hitomi Kirikoshi
(Tokyo University of Foreign Studies)
Ibrahim Mammam
(Direction de la Meteorologie Nationale du Niger)
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2. Land Degradation in Sahel, West Africa
2
＊ Land degradation in the Sahel
ｒ apid population increase
low technology in agriculture
overgrazing
(Ayatunde 2000, Mortimore and Turner 2005, Tschakert 2007)
＊ Continuous cultivation and overgrazing
water and wind erosion

3. Downward Spiral
land degradation
hunger and poverty
armed conflict (farmers and herders)
terrorism (Boko Haram)
mass emigration from West Africa to Europe
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4. Research village
Annual precipitation 445mm 4

5. Strong wind and
rainfall ：
loss of topsoil and
exposure of sedimentary
layers
= Land degradation
Plant biomass is decreased
and
termite mounds are diminished
because of a food shortage
for termites.
Previous
ground level
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6. Soil type: Arenosol [FAO 1971]
sandy soil, poor soil nutrition
mainly with quartz.
This soil type spreads over Sahel
from Mali to Lake Chad through
Niger
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7. People collect the waste
from their house yards.
Anti-desertification methods (2):
waste input
on the degraded land
The waste includes ｌ ivestock
dung, plant residue,worn-out
clothes and sandals etc.
7

8. They deposit urban waste on the degraded land of crop fields.
They pile the organic matter,
metal and plastic wastes
to catch the blown sand.
Blown sand
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9. Chemical property of field, degraded land and urban waste
pH
Total
N
Total
C C/N
Exchange Cation
cmol(+)/kg P
H2
O N( ％ ) C( ％ ) Na K Ca (mg/kg)
Rural Area
pearl millet field
(kasa) 6.4
0.01
0.12 12 0.01 0.04
0.4
8
degraded land
（ foko ） 4.4
0.01
0.09 9 0.02 0.12
0.2
7
Urban Area
Urban waste
(jibuji) 7.4 0.17 2.27 13 0.75 0.31 37.4 365
Soil type kasa shows weak acidity and abundant soil nutrients.
Nutrition accumulated in urban waste.
In comparison with most fertile crop fields, urban waste contained
17 times of nitrogen, 8 times of potassium and 9 times of calcium,
46 times of phosphate
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10. PLOT2 ： 5kg/m2
PLOT3 ： 10kg/m2
PLOT4 ： 20kg/m2
PLOT5 ： 45kg/m2
On site Experiment
I made on site experimental plots and scattered the urban waste (2008).
We continue to monitor the condition of soil and plant growth. 10

11. PLOT 2 ： 5kg/m2
PLOT 3 ： 10kg/m2
PLOT 4 ： 20kg/m2
PLOT 5 ： 45kg/m2
Aug, 2010
(2nd
year)
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12. PLOT 4 A new termite mound
(Nov. 2009)
Growing termite mound (Aug. 2010)
Restarting biological process
After urban waste input, we could see
the termite activities on plot 2 through
plot 5 and a termite mound had grown
in plot 4.
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13. PLOT 4 ： 20kg/m2
PLOT 5 ： 45kg/m2
Sep, 2018
(10th year)
Based on my plant growth observations, the critical amount
of urban waste for land restoration was at least 20 kg/m2
,
2 cm thick on the ground.
My results indicated that Hausa practices helps to generate
grassland and prevent soil erosion.
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14. ■ the heaps of urban waste on the ground
1. catchment of the wind-blown sand and organic matter
Eight Effects of urban waste input for land restoration
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15. ■ biological activities of termite
2 ． Termite bring up the small grain of clay and silt. They mixed
up
sand, silt and clay for improving the soil property.
3 ． Termite drill the tunnels into the cemented ground and
improve
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16. ■ improving the soil chemical property
5. Urban waste are alkaline and neutralize the soil acidity of the
degraded land
6. adding the nutrition of N, K, P and other nutrients
■ seed contained and germination
7. seed germination from urban waste and growth of useful plants
■ 8. plastic bags prevent water evaporation (suitable for termite)
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17. Social Experiment: October 2011
Urban waste input
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In 2011, with the cooperation of local residents, I piled 150 tons
(6cm thickness) of urban waste on a 50 × 50-m fenced plot of
degraded land.

19. 19
Put soil and sand slightly on the urban waste
1cm thick sand on the urban waste

20. We herded livestock onto the
rehabilitated land, and they
fed on the grass within the
fenced area.
We continued to keep the
animals within the fence
even after all of the grass
was consumed.
The livestock dung
maintained the soil quality.
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21. We found 13 tree species
germinating from the livestock
dung and shrubs growing
within the fenced area.
They are useful tree species
(livestock fodder, cooking
dishes, famine relief foodstuff
etc)
（ a ）
（ b ）
（ c ）
（ e ）
（ d ）
（ f ）
(a) Balanites aegyptiaca
(b) Borassus aethiopium
(c) Piliostigma reticulatum
(d) Zizyphus mauritiana
(e) Adansonia digitata (baobab)
(f) Faidaherbia albida
Livestock can induce the
land restoration suitable
for pastoral camps.
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Baobab tree

22. Seventh year (Sep 2018 ): Herders enjoy conversation in
the tree shade during their livestock grazing.
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Expanding the sites
Carrying urban waste
from capital city,
Niamey
dump car 20 ton / time
tractor 3.5ton / time
2015 Oct-2018 Sep
three years
34 sites, 10.0 hectares
2,303 ton urban wastes

24. Cleaning the city,
Hotel waterCollecting urban waste
1.1 million population
(Niamey, 2015)
Waste at urban center
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greening the land.
(Minimizing the urban waste, maximizing the land resource)

26. 26
Cleaning the city, greening the land
I aim to counter the popular belief that urban waste and
livestock are destroying the land.
In densely populated areas of Sahel, I propose that
urban waste and livestock can instead be used to
restore the degraded land. (City concentrates nutrition.)
2012 Feb 2018 Sep

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