Mr Giregon Olupot, School of Agricultural Sciences Makerere University, Uganda. Global Symposium on Soil Erosion (GSER19), 15 - 17 May 2019 at FAO HQ.

1. Erosion-induced soil toxicity undermined maize-
bean responses to sustainable land management
practices on Mount Wanale in eastern Uganda
John Bosco Tukundane, Twaha Ali Ateenyi Basamba, Patrick Musinguzi, Emmanuel
Opolot, Giregon Olupot*, School of Agricultural Sciences Makerere University P. O. Box 7062,
Kampala, Uganda, *giregono@gmail.com
This study was informed by the poor crop
performance observed under a World Bank
(WB)-supported sustainable land
management (SLM) project to restore Mt
Wanale ecosystem in eastern Uganda
blighted by decades of accelerated soil
erosion (Plate 1). Among the SLM practices
on the ground included contours with tie
bands, reduced tillage, fertiliser NPK
application and manuring. The study was
aimed at identifying cause(s) for the observed
poor crop performance beyond the
explanation from implementers of the SLM
project, that farmers’ soils were
nonresponsive’. We hypothesized that poor
crop performance was due to soil toxicity
induced by decades of unabated accelerated
soil erosion.
This study was conducted in Wangasa village,
Bunatsoma parish, Wanale Sub-County, Mbale
district in eastern Uganda. Wanale is located
about 6.8 km to the south east of Mbale
Municipality at 1003’14.2”N and 34014’24.9”E
at an elevation of 2092 meters above sea level
with slopes of steepness 30 – 60% (Plate 1). To
test our hypothesis, we collected and analysed
bulk soil samples sampled to 0 – 15 cm depth
for physico-chemical properties using standard
protocols. These included pH(2.5H2O:1soil),
SOM (%), total N (%) following Kjeldhal
Method, plant-available P by Bray I Method,
exchangeable bases, and soil texture (by
Hydrometer Method). Data collected were
checked for conformity with the conditions for
conducting ANOVA and analysed using the
Genstat statistical package 12th edition.
INTRODUCTION MATERIALS AND
METHODS
The soil pH of the study site is in the range of
Al3+, Fe3+ and Mn2+ toxicity to plants and
together with the low levels of SOM, could be
the reasons for poor crop responses to the
SLM practices on Mt Wanale. Raising the soil
CONCLUSION
Soil textural class was silt clay loam, ranging
from 26 ± 2.46 to 31 ± 2.46 (%clay), 32 ± 5.01
to 42 ± 5.01% (%silt) and 32 ± 2.80 to 37 ±
2.80% (%sand) (Table 1). Soil water ranged
from 0.29 ± 0.02 g cm-3 to 0.31 ± 0.02 g cm-3
(field capacity, FC) and 0.17 ± 0.02 g cm-3 to
0.17 ± 0.02 g cm-3 (permanent wilting point,
PWP) (Table 1).
Plate 1. Location of Mt Wanale (top left), very steep
landscape (top middle) and red soils with miserable maize
(top right) contrary to vigorous bananas and climbing
beans on farmers’ own plot which had been used as a pen
for zero-grazing dairy cattle (extreme left of middle row)
and total maize failure in one of the ‘best’ SLM practices
(middle of middle row). Contour cultivation (extreme right
of middle row) as one of the interventions to combat water
erosion. Notice vigorous bananas+beans+ maize and
maize+finger millet+banana intercrops with yams in the
Dokho flood plain (left and middle bottom row) where
eroded soils are deposited and compost from one of the
windrows due for sieving at the Mbale Municipal Solid
Waste Composting Plant.
Table 1. Mean soil physico-chemical properties under selected soil conservation practices from the World Bank sustainable land
management project on Mt Wanale, eastern Uganda as of June, 2016.
pH SOM N P K Clay Silt Sand FC PWP
Treatment (%) (mg kg-1
) (cmol kg-1
) (%) (g cm-3
)
Bean CT 3.5 1.52 0.12 14.2 0.61 28 39 33 0.31 0.17
Bean CT+Comp 4.1 1.42 0.08 14.7 1.65 29 38 33 0.30 0.16
Bean CT+Comp+R 3.3 1.85 0.13 14.2 0.75 27 41 32 0.30 0.15
Bean ZT+R 3.7 0.40 0.08 18.6 1.51 28 40 32 0.30 0.16
Bean ZT+R+B 3.6 0.79 0.02 12.7 1.05 31 33 36 0.31 0.17
Maize CT 3.8 1.44 0.10 59.8 1.02 29 36 36 0.30 0.16
Maize CT+Comp 3.9 1.69 0.10 13.7 2.11 29 38 33 0.31 0.17
Maize CT+NPK 4.2 2.05 0.11 42.1 0.92 31 32 37 0.30 0.17
Maize CT+NPK+Comp 3.4 1.98 0.14 12.7 1.12 26 41 33 0.29 0.15
Maize ZT+Comp 3.6 1.62 0.13 18.1 0.96 26 42 32 0.29 0.15
Maize ZT+Comp+B 4.6 1.12 0.09 20.6 1.86 27 39 34 0.29 0.15
Maize ZT+NPK 4.9 0.86 0.08 21.6 1.32 28 39 33 0.29 0.15
Maize ZT+NPK+B 4.3 1.78 0.08 25.5 1.44 30 36 34 0.31 0.17
Maize ZT+Comp+NPK 4.9 0.86 0.08 21.6 1.32 28 39 33 0.30 0.16
Maize ZT+Comp+NPK+B 3.7 1.06 0.06 21.1 1.51 28 38 34 0.30 0.16
P-value 0.206 0.51 0.100 0.977 <.001 0.279 0.746 0.815 0.598 0.354
L. S.d 1.197 0.68 0.063 75.05 0.963 5.074 4.929 5.764 0.018 0.025
S.e 0.58 0.69 0.031 36.43 0.468 2.46 5.01 2.8 0.009 0.012
Critical values 5.5 3.0* 0.25* 15* 0.4**
Key: conventional tillage(CT), compost(Comp), rhizobia(R), zero tillage(ZT), planting basins(B)
The soils were severely acidic, pH ranged from
3.3±0.58 under Bean+ZT+Compost+R treatment
to 4.85±0.58 under maize+ZT+NPK treatment
(Table 1). The SOM and N were also below
critical limits but plant-available P and
exchangeable K exceeded critical limits (Table 1).
MAIN RESULTS pH to ≥ 5.0% and SOM to ≥ 3.0% using
locally available amendments such as wood
ash and municipal solid waste compost (pH
≥ 9.0)
(Plate 1bottom right) should have preceded
investment in the costly SLM practices,
paving a way towards restoring the landscape
to its original ecosystem prior to
encroachment.