Soil fertility depletion is a major constraint for agricultural productivity under smallholder farming systems in sub-Saharan Africa. The NUTMON toolbox was used to determine on-farm nutrient balances in Central Uganda to come up with plausible recommendations to advance increased soil productivity and household food security and incomes among smallholder farming systems in Wakiso district. Farm balances for major nutrients (N, P, K) at crop level (Primary Production Units – PPU) for major crops i.e. banana, sweat potatoes, beans and maize were all negative during the monitoring period, thus indicating a net mining of nutrients through crop harvest.

1. MONITORING NUTRIENT FLOWS, NUTRIENT BALANCES AND
ECONOMIC INDICATORS OF SMALLHOLDER FARMS IN LUKWANGA
PARISH, WAKISO SUB COUNTY, WAKISO DISTRICT.
Baseline Survey Report, July – December 2002
By
Joshua Zake *
Florence Nagawa *
Charles Walaga *
Andre de Jager **
*Environmental Alert, P.O. Box 11259 Kampala, Uganda
** Agricultural Economics Research Institute (LEI), P.O. Box 29703 The Hague,
The Netherlands.

2. 2
1.0 Introduction
The Agriculture sector in Uganda employs more than 80% of the population and
contributes about 45% of the gross domestic product (GDP) (MFPED 2001).
Agricultural production is based on smallholder production with about 3.0 million
households cultivating less than 2 hectares each. Over half of the total agricultural
gross domestic production (GDP) (56%) is subsistence production for household
consumption (MFPED 2001). Ugandan agriculture is characterized as ‘traditional’
because traditional farming techniques and practices are used far more than the green
revolution technologies. Most of these management techniques and practices used are
poor and/or inappropriate resulting into soil mineral extraction, structural degradation
and soil erosion and hence very low productivity. In fact, improved planting and
stocking materials, inorganic fertilizers, and chemical pest and disease control
measures are rarely employed by the farmers as they are often not economical, not
appropriate for the local conditions, not available and are beyond the reach of the
majority of the farmers. For example, inorganic fertilizer use in Uganda is estimated at
1 kg of plant nutrients per hectare. It is clear how low this level is when compared to 9
kg/ha, the average for sub-Saharan Africa, which in turn is only 5% and 20% of that
used in East Asia and Latin America respectively.
Soil nutrient depletion has been identified as one of the major biophysical constraints
to food security and economic development in the agriculture dependant rural areas of
Uganda. Previous research has revealed the relatively low nutrient stocks and declining
productivity with negative nutrient (Nitrogen, Phosphorus, Potassium) balances
(Sanchez et al., 1996, Stoorvogel et al, 1993, Shephered et al,1995 and 1996, Wortman
1999, Wortmann et al, 1998, Stoorvogel and Smailing 1990, Henao and Neidert 1999,
Wortmann et al 1998 and Walaga C.1999). A project to explore soil fertility
management improvement opportunities was initiated in Wakiso District, Lukwanga
Parish in 2002. As a baseline activity, a survey to establish the nutrient flows, balances
and economic performance of smallholder farmers was conducted in the parish.
1.1 Specific Objectives of the Survey
(i) To establish the status of nutrient balances and economic performance of
farms in parish and hence the productivity and sustainability of farming
systems.
(ii) To evaluate the present nutrient management/ soil fertility management
technologies in the parish.
(iii) To identify potential soil nutrient management technologies for the area for
experimentation in the Farmer Field Schools.
2.0 METHODOLOGY
2.1 Data Collection

3. 3
i. Sensitization on the objectives of the project was carried out in the area for
the farmers, local civic leaders, policy makers and technical personal. 28
volunteer project farmers were then selected. The selection criteria was
willingness to participate in Farmer Field Schools (FFS), a member of a
local farmers group, is involved in mixed farming (crops and livestock)
ii. Farm surveys and farmer interviews were conducted for 28 farms to identify
soil types as perceived by farmers, identify the soil fertility management
practices and technologies practiced in the area. For each farm, Farm
Section Units (FSU) were demarcated based on soil properties such as
color, depth, texture, slope, flooding regime and nature of land ownership.
iii. Farm sections and enterprises were discussed with farmers based on
Vlaming et al, 2001. and participatory nutrient flow modeling conducted.
Farmers then identified the different Farm Section Units (FSU), Primary
Production Units (PPU), Secondary Production Units (SPU), Nutrient
Redistribution Units (RU) their interrelationships and their relationship with
the outside.
iv. Slop gradient and length for each FSU were measured using a Clinometer.
Estimates for size of FSU, PPU, SPU and RU were measured using paces
and then converted to meters.
v. For each farm, a composite soil sample was taken from each Farm Section
Unit (FSU) at a depth of 30 cm. Analysis was conducted at Makerere
University Department of Soil Science Research Laboratory for total
Nitrogen (N), total Phosphorus (P), total Potassium (K), Organic matter
(%Om), pH, bulky density and Soil texture as in Okalebo et al (1993).
vi. Nutrient monitoring questionnaires (Vlaming et al, 2001) were used to
monitor nutrient and economic flows for a period of six months (July –
December 2002). This involved the gathering of information on nutrient
flows (inflows and out flows), prices for inputs and outputs and farm
inventories.
vii. Nutrient (N, P, K) contents of other materials including livestock
dung/manure, crop materials and residues were gathered from literature.
viii. Rainfall/precipitation data was obtained from Kawanda Research station,
which is the nearest station to the research areas.
All data gathered was entered and analyzed using the NUTMON toolbox version 2,
2002 to determine Nutrient flows, Nutrient balances for NPK and economic indicators
at farm level and production unit level (PPU and SPU levels). These parameters were
exported to SPSS 8.0 version for windows to determine tables for means.
3.0 RESULTS
3.1 Study Area
Lukwanga parish is located in Wakiso Sub County, Wakiso District. Wakiso District
surrounds Kampala city and is within a distance of 20 to 50 km from the City center.

4. 4
Generally the area receives mean annual rainfall of 1320 mm with areas bordering on
lake Victoria getting between 1750 and 2000 mm. There are two major wet seasons
running from April to May and October to November with principal peaks in April and
a minor one in November. Average monthly days of rainfall are 10 (WDLGBFP 2001).
The dominant soil types in the sub-County (and district) are red gravel loams with
occasional murram, reddish brown sandy, red clay loam and yellowish sands with
quartz gravel with moderately low Soil fertility. In the wetlands, the soils are gray
sands whose parent material is alluvium and hill wash, gray coarse sands from lake
deposits, black and gray clays from river alluvium and peat sands and clay formed
from papers residue and river alluvium.
Subsistence agriculture mainly occurs with bananas and coffee dominating hence the
coffee- banana perennial farming systems characterization. However in the present
farming system coffee as a traditional cash crop is gradually being replaced by food
crops as a major source of income for the families. Important food and cash crops
grown now include beans, cassava, sweet potatoes, maize, sugarcanes, cocoa, avocado,
jack fruits, pineapples, passion fruits and vegetables (tomatoes, egg plant, cabbages and
onions). In addition households keep cattle, goats, pigs and poultry under different
systems ranging from conventional confined and semi confined systems to the
dominant traditional free-range systems (tethering, open grazing and free range). Table
1 is a summary of the average farm asset values and soil fertility status.
Table1. Soil fertility status and farm assets values in Lukwanga Parish
Characteristics
Land
Total farm area (Ha) 3.1
Total cultivated area (Ha) 1.4
Fallow area (Ha) 1.7
Average slop (%) 7.3
N stock (Kg/Ha) 8934
P stock (Kg/Ha) 7351
K stock (Kg/Ha) 11490
Capital
Total Tropical Livestock Units 2.3
Value of Livestock (Ush. /farm) 993750
Value of Land (Ush. /farm) 3883852
Value of equipment (Ush. /farm) 96536
Total capital (Ush. /farm) 4974138
3.2 Farmer’s Soil characterization Vs Scientific characterization
The major criteria farmers’ use in soil classification are level of fertility, physical
properties including color (degree of blackness/redness/darkness), easiness or
difficulty of cultivation, structure (weak, strong and stoniness’ i.e. proportion of
sand and clay), drainage and water holding capacity and depth or thickness.
However soil color is used as a most important criterion of classification and soils
are named after their colors, but farmers appreciated that at times the darkness of

5. 5
the soil may be related to its fertility but also urged that this is quite subjective because
they identified reddish brown soils, which were fertile as depicted by the crops and
vegetation growing on them.
Table 2. Characterization of the soils of Lukwanga parish.
Farmers’ soil name Farmers characterization Laboratory analytical results
Soil pH
% Om
Total N
Available P
Available K
(i) Limyuffu (red soil) Properties: Clayey, strong
structure and shallow.
Major crops grown include
banana, beans, groundnuts,
cassava, coffee, vegetables as
Trees such as paw paw,
jackfruit, and Ficus species are
grown.
Constraints – shallow, soil
erosion and associated with
rotting of root tubers.
Potentials – its good for crop,
which derive nutrients on the
surface such as beans,
vegetables and groundnuts.
Mainly distributed along
Upper slope
Soil texture: sand: clay: silt
Soil pH
% Om
Total N
Available P
Available K
(ii) Limyuffu (red soil) Properties: Deep soil with a
weak structure and good water
holding capacity.
Banana, beans, groundnuts,
cassava, coffee, vegetables as
major crops grown. Trees such
as paw paw, jackfruit, and
Ficus species are grown.
Dorminant weeds include
Comelina spp, coach grass.
Other practice is grazing.
Constraints – Soil erosion
Potentials – its good for most
crops.
Mainly distributed along
Upper slope
Soil texture: sand: clay: silt
Soil pH(iii) Bumba (Clay soil) Properties: Deep soil and
water logged.
Eucalyptus is the major crop.
Other activities include brick
lying and grazing animals.
% Om

6. 6
Total N
Available P
Available K
Constraints – water logging
and a breeding environment
for mosquitoes.
Potentials – its good for
cultivation of water loving
crops such as yams, and rice.
Mainly distributed in Valleys
(swamps) Soil texture: sand: clay: silt
Soil pH
% Om
Total N
Available P
Available K
(iv) Kiwugankoffu (Greyish
soil)
Properties - Porous with a
weak structure and has a poor
water holding capacity,
therefore dries very fast. Poor
soil fertility.
Major crop is Sweet potatoes.
Agro forestry trees grown
include: Albizia spp,
Markhamia spp, and mango.
Dominant weeds is Lusenke
Constraint – loses water
quickly, low soil fertility.
Potentials – allows air and
water to enter.
Mainly distributed in lower
slops towards valleys.
Soil texture: sand: clay: silt
Soil pH
% Om
Total N
Available P
Available K
(v) Lunnyo (Acid infertile
soil)
Properties - Poor soil physical
properties i.e. poor structure,
water holding capacity and
very low soil fertility.
Major crops include:
bananas, cassava, maize, beans
all showing nutrient deficiency
symptoms, most evident was
stuntedness.
Mainly distributed along upper
and middle slops and appears
in patches.
Constraints – Low soil
fertility. Soil texture: sand: clay: silt
(vi) Limyukirivu (reddish
brown soil)
Properties – stony structured
shallow soil with poor water
holding capacity and presence
of termites.
Soil pH

7. 7
% Om
Total N
Available P
Available K
of termites.
Major crops: include bananas,
cassava, groundnuts, and
beans. Also agro forestry trees
grown include mangoes, ficus
spp, and sweet potatoes.
Constraints: Losses water
quickly, low soil fertility as
depicted by dominant weed
spp – Lusenke
Its shallow soil therefore not
good for deep rooting crops.
Potential – presence of macro
organisms (termites enhance
organic matter decomposition
and improve soil aeration.
Its good for crop, which derive
nutrients on the surface such as
beans,
Soil texture: sand: clay: silt
Soil pH
% Om
Total N
Available P
Available K
(vii) Kittaka (brown soil) Properties - Clayey soil with
good water holding capacity.
Major crops: include bananas,
cassava, groundnuts, and
beans. Also agro forestry trees
grown include mangoes, ficus
spp
Constraints: forms a film on
the surface on drying which
impedes seed germination and
water infiltration, low soil
fertility.
Potential – has a good
structure and conserves soil
moisture.
Soil texture: sand: clay: silt
Soil pH
% Om
(viii) Eridugavu (Dark soil) Properties – loamy structured
deep soil with good water
holding capacity.
Major crops: include bananas,
cassava, groundnuts, and
beans. Also agro forestry trees
grown include mangoes, ficus
spp, and sweet potatoes.
Constraints: forms a film on
the surface on drying which
impedes seed germination and
Total N

8. 8
Available P
Available K
impedes seed germination and
water infiltration, low soil
fertility as depicted by stunted
crops.
Its shallow soil therefore not
good for deep rooting crops.
Potential – has a good
structure and conserves soil
moisture.
Its good for all crops (deep and
shallow rooted).
Soil texture: sand: clay: silt
3.3 Farmer’s measure for Soil fertility
Farmers’ indicators of soil fertility are increasing/constant crop yields and crops ability
to complete life cycles and less deficiency symptoms observed on crops.
They could asses soil fertility depletion as a translation to decline in crop yields,
numerous deficiency symptoms as stuntedness and yellowing in leaves and the fact the
it must that they have to fertilize their soils in order to obtain any crop yield.
A feedback on soil analysis results for specific farms greatly excited farmers, being the
first time for their soils to be analyzed but it also enhanced their participation.
3.4 Farmer’s perception of Nutrients
The concept of Nutrients, Nutrient flows and balances were completely new to all the
farmers. Farmers understood nutrients as inputs such as manure and inorganic
fertilizers that are added to the soil to improve soil fertility and productivity. They did
not have knowledge of the different nutrients, their roles and dynamics. Therefore time
was spent on describing to farmers the role of nutrients in soil fertility and their
movement into and out of the farm. Farmers were then able to identify the various
nutrient flows and pools on their farms. The nutrient flows discussed with farmers as
being the most significant are given in table 3. A summation of these flows gives the
Nutrient balance for each farm.
Table 3 The following Nutrient flows were observed as
Flow label Flow type
Inorganic fertilizers and feeds IN 1
Imported Organic fertilizers and feeds IN 2a
Imported manure from external grazing IN 2b
Wet and dry atmospheric deposition IN 3
Symbiotic N fixation IN 4a
Non symbiotic N – fixation IN 4b
Harvested products OUT 1
Exported crop residues and manure OUT 2a

9. 9
Excretion of manure outside the farm OUT 2b
Leaching from soils OUT 3a
Leaching from redistribution units OUT 3b
Gaseous loss from the soil OUT 4a
Gaseous loss from the Redistribution units OUT 4b
Erosion OUT 5
Human excreta OUT 6
Adopted from Vlaming et al., 2001.
The FFS approach would be valuable in introducing the farmers to the concept of soil
nutrients, their roles and dynamics. The knowledge achieved would enable farmers to
become more efficient managers of soil nutrients on their farms and innovators in soil
fertility management.
3.4 Nutrient Balances at Farm level
Nutrient monitoring is a method that quantifies a system’s in flows and outflows,
resulting in nutrient balances. Nutrient balances can be determined at spatial scales
ranging from national to field level. (Vlaming et al 2001). In this study, Nutrient
balances were calculated as a summation of the nutrient flows on the farms in Table 4.
During this period Negative Total and Partial Nutrient balances for N, P and K were
calculated for the farms in Lukwanga Parish. On average 28 Kg/Ha N, 2.7 Kg/Ha K
and 2.7 Kg/Ha P were lost.
Table 4 Averages of Nutrient flows per farm in Lukwanga Parish
Nutrient flows N (Kg/Ha) P(Kg/Ha) K (Kg/Ha)
Total farm balance -28.3 -2.7 -2.7
Partial farm balance -2.8 -0.2 -0.7
Mineral fertilizer (kg/ha 0.3 0.3 2
Organic fertilizer (kg/ha 3.3 0.6 3.1
Grazing (kg/ha 1.5 0.2 1.6
Atmospheric dep. (kg/ha 2.8 0.5 1.9
Biological fixation (kg/ha) 6.6 0 0
Crop products (kg/ha -3.2 -0.3 -2.0
Crop residues (kg/ha) -0.4 0 -0.3
Manure (kg/ha) -1.5 -0.2 -1.5
Leaching (kg/ha) -22.6 0 -0.7
Gaseous loss. (Kg/ha -7.9 0 0
Erosion (kg/ha -4.6 -3.0 -4.5
Human excreta (in kg/ha) -3.0 -0.8 -0.5
Nitrogen (N) losses were mainly attributed to leaching, gaseous losses, soil erosion and
in harvested crop products.

10. 10
Phosphorus (P) losses were mainly attributed to soil erosion and Potassium (K) losses
to soil erosion, leaching and in harvesting crop products.
Figure 1. Graphical presentation of nutrient ( Phosphorus) flows and balances for one
farm
001
Farm :
Phosphorus - Full Balance kg/acre
full IN 1 IN 2a IN 2b IN 3 IN 4 OUT 1 OUT 2a OUT 3 OUT 4 OUT 5 OUT 6
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
-0.25

11. 11
Figure 2. Graphical presentation of nutrient ( Potassium) flows and balances for one
farm
001
Farm :
Potassium - Full Balance kg/acre
full IN 1 IN 2a IN 2b IN 3 IN 4 OUT 1 OUT 2a OUT 3 OUT 4 OUT 5 OUT 6
0
Despite these losses, there is very little mineral fertilizer use in the area. This is due to
a combination of factors like the high cost of mineral fertilizers, the fear that once used
soil becomes addicted and therefore one has to continue using fertilizers all the time or
no yield will be obtained, and the deterioration in soil structure.
The main nutrient input sources for farmers are organic fertilizers (especially livestock
manures), biological nitrogen fixation and atmospheric deposition. Livestock
management systems in the areas are mostly of the semi intensive type in which
livestock graze on farm on particular farm section units or outside the farm for part of
the day and stay under a tree shed/ kraal during the night. Consequently there is a net
Nutrient inflow into the farm as animals spend more time outside grazing (harvesting
nutrients) i.e. they spend more time feeding than defecating. However in the table
above average quantities of nutrients lost through manure deposited while grazing
almost balances quantities of nutrients gained through grazing because these values are
determined from different farms with various livestock management systems.
3.5 Nutrient balances at crop level for major crops grown in Lukwanga
Nutrient balances (N, P, K) at crop level (Primary Production Units – PPU) for major
crops i.e. banana, sweat potatoes, beans and maize were all negative during the
monitoring period (Table 5) indicating a net mining of nutrients through crop harvest.

12. 12
However N balance with respect to bean monocrop is positive due to less nitrogen
being harvested in the bean crop than the Nitrogen inflows which are boasted by the
biological nitrogen fixation (BNF) of the bean monocrop.
Table 5 Averages of Crop yields and Nutrient balances for major crops in
Lukwanga Parish as per current practices
Crop Crop yield
(Kg/Ha)
N (Kg/Ha) P (Kg/Ha) K (Kg/Ha)
Banana Monocrop 1750 -34 -5 -6
Sweat potatoes 1696 -37 -8 -13
Bean monocrop 1873 12 -5 -61
Maize intercrop 1879 -17 -10 -28
The farms in the area are basically depending on the mining of nutrient stocks for their
agriculture production. Considering the relatively low nutrient stocks of the farm soils
(table 1), the farming system is not sustainable.
3.6 Economic indicators at Farm level
Net farm income during that period was positive and relatively high (Table 6).
Total gross margin for crops was also positive and relatively high, an indication of the
high levels of commercialization of crop production. Crops contributed 37% of gross
farm value sold as market share.
Both Farm net cash flow and Household cash flow were positive but the later was
slightly higher due to additions from off farm income from household members.
On the other hand Total gross margin and gross margins for Secondary Production
Units (SPU) were negative depicting that during this period much cash was invested
for growth and expansion of these units than was realized from sale of products from
these units. Alternatively it could be that most of the products from these units were
consumed at home and hence never generated cash.
Table 6. Average economic indicators for Lukwanga Parish
Indicator Mean
Net farm income (in Ush) 838,650
Total gross margin PPU's (in Ush) 917,959
Gross margin PPU's (in Ush/ha) 323,475
Gross margin PPU's (in Ush/day) 4,223
Total gross margin SPU's (in Ush) -39,065
Gross margin SPU (in Ush per TLU) -31,640
Gross margin SPU (in Ush/day) -122
Total gross margin RU's (in Ush) 180
Off farm income (Ush) 19,595
Off farm income (in Ush per day) 1,086
Family earnings (in Ush) 858,246
Family earnings (in Ush per consumer unit) 138,767
Farm net cash flow (in Ush) 496,788

13. 13
Household net cash flow (in Ush) 516,383
Market share (% of gross value sold) 37
4.0 Discussions
Farms in Lukwanga parish are strategically located near the capital city and have
exploited that location through orienting their farms to production for the market.
However, nutrients balances as indicators of farm production sustainability are
negative because more nutrients are being lost to the farms than those gained. Most of
the nutrient losses are through harvested crop products which are sold. Improving
nutrient balances by reducing nutrient losses, improving efficiency of recycling and
low external inputs would result into a positive balance and would greatly improve the
productivity and sustainability of the farms in the area.
Nutrient losses as a result of leaching and soil erosion can be minimized through
increasing Soil organic matter (SOM) levels, cover crops and composted manures,
integrating appropriate agro forestry tree species into the farming system, use of soil
and water conservation practices such as fanya juus and fanya chini across the slope;
mulching and intercropping. The leaching and gaseous loss of Nutrients from the
Redistribution Units (RUs) like stables, compost pits and manure heaps, can be reduced
through proper handling and protection. For example, stables should be roofed and
have concrete floors, compost pits and manure heaps should preferably be placed in a
flat area and shade.
Additionally technologies associated with nutrient inflow can also be integrated in farm
management. For example:
i. Enhancing biological nitrogen fixation through inoculation with Rhizobia.
ii. Increasing livestock confinement for more efficient collection of dung and
urine on farm. Under this system even more Nutrients are brought into the
farm especially when the livestock is fed on supplements such as maize
brand, cotton seed cake, molasses etc in addition to imported grass (Napier)
and crop residues.
iii. Increased and efficient use of mineral fertilizers
iv. Importation of organic manures especially poultry manure which is being
practiced in the area.
However, in spite of the presence of all these possibilities, and the relatively high levels
of farm commercialization which is a prerequisite for investing in soil fertility
management, it was discovered that:
i. Farmers’ knowledge of soil nutrients and their dynamics was insufficient to
inform farmers decision making in soil nutrient management. Hence, the
need for basic training in the science of soil nutrients and their dynamics.
This posses a major challenge considering the low levels of literacy in the
area.

14. 14
ii. Low levels of awareness of soil fertility issues among local policy makers to
provide for the necessary local policies and resources to support improved
and more efficient soil fertility management.
5.0 CONCLUSION
The project inception phase in the parish has succeeded in raising the awareness of the
community about the status of the productivity and sustainability of their farming
systems. Farmers have agreed to participate in soil fertility Farmer Field Schools (FFS)
to learn about soil nutrients and to try out technologies that can improve the fertility
and productivity of their soils.
6.0 REFERENCES:
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systems in eastern Africa with special reference to crotalaria) C.
chroleuca G. Don). Ph.D. dissertation, Swiss Federal Institute of
Technology, Zurich.
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agricultural production in Uganda. Draft, International Fertiliser
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Mexico City.
Shephered, K.D., Ohlsson, E., Okalebo, J.R., Ndufu, J.K., David, S., 1995. A static
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Kenya to explore the possible impact of improved management.
Shephered, K.D., Ohlsson, E., Okalebo, J.R., Ndufu, J.K., David, S., 1996.
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Stephens, D., 1996. The effects of fertilizers manure and trace elements in continuous
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Stoorvogel, J.J., Smailing, E.M.A, 1990. Assessment of soil nutrient depletion in
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Tenywa M. Makooma, Bekunda A. Mateete, Lufafa Abel and Taulya Godfrey,
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– 6th
May 1999. SWCSU
TECHNICAL REPORT No. 2
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0
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317 419000 E-mail: notmon-support@alterra.Wag-ur.nl
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3615624
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