Mr Samuel Tetsopgang, University of Bamenda, Cameroon. Global Symposium on Soil Erosion (GSER19), 15 - 17 May 2019 at FAO HQ.

1. Increasing soil chemical properties
through the application of rock fines in
tropical soils in west Cameroon, Africa
Samuel Tetsopgang, Fabrice Fonyuy, Tongwa F. Nkengafac, Okon E. Morio,
Abeng Dang G., Meleng Dang G. Department of Geology, HTTC, University of Bamenda,
Bambili-Bamenda, Cameroon
INTRODUCTION
The economic damage of soil erosion is
alarming in sub-Sahara Africa. In Zimbabwe
alone, it is estimated that farmers loose
three times more nitrogen and phosphorus
by erosion than they apply to their fields.
Then soil erosion is a burden for agricultural
productivity and has rendered soils depleted
in essential nutrients necessary for crop
growth in Africa. According to Smaling et al.
(1996), the average N, P and K balances for
Africa in 1983 were -22, -2.5 and -15 Kg ha-1
yr-1, respectively. In fact, these nutrients
were lost through exported harvested
products and erosive processes such as
water runoff and wide spread eroding
sediments that caused negative balances.
Then, adding NPK chemical fertilizers is the
common method used by farmers in sub-
Sahara Africa to solve the problem of soil
depletion in these chemicals. However this
application of NPK chemical fertilizers on
soils has negative consequences. There is a
need to look for an alternative to supply
soils with eroded chemicals. This work
focuses on the application of fines from
different types of rocks to combat chemical
loss in soils.
METHODOLOGY
Fresh rock samples made up of basalt,
trachyte and volcanic pyroclastic materials
in addition to limestone and gneiss locally
collected were crushed into smaller
fragments then ground several times into
fines and sieved with a 1x1mm mesh sieve
and used as fertilizers. Poultry manure or
cow dump were added to some treatments.
Soil samples were collected from 06
different field trials from 06 localities in
Cameroon. The test crops were chosen
based on the potentially of a plant to rapidly
grow on a specific site and made up mostly
of maize. However cabbage, potatoes and
carrots were also used as test crops in some
sites. The experimental trials were made up
of the controls and treatment soils. Soil
samples were collected and taken for further
description and analysis in the Laboratory of
Soil Sciences, Faculty of Agronomy,
University of Dschang, Cameroon.
Parameters such as pH, OM and OC (%), N
(g/Kg), Ca, Mg, Na and K (meq/100 g) and P
(ppm) were determined using specific
methods of soil analyses.
They are made up of texture and chemical
compositions of control and treated soils.
Control soils: Control soils show textures
belonging to the fields of loamy sand (T01
and T02) to clay (T03) passing through clay
loam (T06) and silty clay (T05). The pH
values vary between 7.1 and 4.6 and organic
matter between 7.2 – 0.95 % for CO, 9.3-
1.64 % for MO and 4.6 – 0.06 g/Kg for N.
For the exchangeable cations, Ca exhibits
highest values of 3.8 meq/100g while lowest
values belong to Na with 0.00 meq/100g. K
and Mg exhibit values between 3.2 – 0.0
meq/100g. Available phosphorus (P) values
are between 26.5 and 6.8 ppm for these
controls.
Treated soils: The textures of different
treated soil samples were plotted on the
field of sandy loam (T12, T22 and T62) and
clay (T13, T23 and T45). However, some
treated samples presented properties of clay
loam (T26 and T46) and laomy sand (T41).
The highest (= 7.2) and lowest (4.8) pH
belong to T41 and T15, respectively. The
organic matter vary between 7.0 – 0.2 % for
CO, 12.1 – 0.4 % for MO and 5.5 – 0.1 for N
(g/Kg). For the exchangeable cations, the
highest values (= 45.8 - 24.0) and (= 10.2 –
0.9) belong to Mg and Ca, respectively.
Lowest values (= 0.1 - 0.0) are those of Na.
K also exhibits low values (= 1.8 – 0.0). The
higher (= 48.9) and lower (= 8.8) capacity of
cationic exchange (meq/100g) were found
on T23 and T25, T35 and T45, respectively.
The highest available phosphorus (P) values
of 96.0 ppm was found on sample T46.
Other higher values of P are encountered on
T62, T22, T23 and T24 with 50.9, 51.5, 32.7,
and 30.1, respectively.
Figure: Variation of chemical properties of controls (T01, T02,
T03, T04, T05 and T06) and different treatments (T41 to T46) of
soils collected in different localities in Cameroon. T01, T02, T03,
T04, T05 and T06 are control soils collected in 06 different
localities in Cameroon. T41 = T01 + 600g basalt fines + 600g
poultry manure; T12 = T02 + 2Kg basalt fines; T22 = T02 + 2Kg
limestones fines; T62 = T02 + 1Kg limestone; T13 = T03 + 3Kg
basalt fines; T23 = T03 + 3Kg gneiss fines; T24 = T04 + 200g
fines from volcanic (basaltic) pyroclastic materials; T15 = T05 +
1Kg basalt fines; T45 = T05 + 1kg basalt fines +0.5 Kg green
manure (Tithonia Diversifolia); T26 = T06 + 2Kg basalt fines +
0.75Kg green manure (Tithonia Diversifolia); T46 = T06 + 2Kg
trachyte fines + 0.75Kg green manure
increase with the application of the basaltic
fines. There is a slight increase of OM for
some samples. However, samples T04 and
T24 exhibit an increase of OM from 4.5 to
9.1%, and sample T01 and T41 indicates an
increase from 9.3 to 11.3%. These treatments
also were treated with basalt fines. Then,
this may also suggests that basalt fines also
increase OM contents in different
treatments. N contents remained very weak
except high values of more than 2.8 g/Kg for
sample T41, T15 and T45. These samples got
treatment made up of basalt fines and
poultry or green manure. Added N came
from manure. After different treatments
with rock fines, Na remains unchanged and
K values slightly increase to 0.8 - 1.1
meq/100g. However, there is a remarkable
high values of Mg and Ca on some samples
with treatment of basalt and trachyte fines.
This suggest these rocks as a source of Ca
and Mg in soils. For P, there is a general
increase in relation to the controls in most
soil samples after treatment (Figure). The
highest values of 96.0, 51.5 and 50.9 ppm
were found on soils treated mostly with
trachyte and limestone, respectively. Higher
P contents of 32.7 and 30.1 came from
treatments with fines of gneiss and volcanic
pyroclastic materials.
CONCLUSION
Rock fines from basalt, trachyte and
volcanic pyroclastic materials in addition to
limestone and gneiss were applied as
fertilizers in several localities of west
Cameroon. After treatments, there is slight
increase of pH in all samples. However,
there is a remarkable pH increase in
treatments with basalt fines. Then the
application of fines from these rocks may be
used to manage the soil acidity. These basalt
fines also increase significantly the soil
content in Mg and Ca. The higher values of P
suggests that the application of fines from
rocks such as trachyte, limestone, gneiss and
basalt as a potential source of phosphorus in
soils.
REFERENCE
Smaling, E.M.A., Nandwa, S.M. and
Janssen, B.H. (1997) Soil Fertility Is at
Stake, in Replenishing Soil Fertility in Sub-
Saharan Africa. In: Buresh, R., Sanchez, P.A.
and Calhoun, F., Eds., American Society of
Agronomy and Soil Science Society of
America, Madison Wisconsin, 47-61.
pH
Ca
Mg
OC
OM
P
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
T01 T02 T03 T04 T05 T06 T41 T12 T22 T62 T13 T23 T24 T15 T45 T26 T46
Chemicalproperties(pHw,Ca,Mg,OC,OMandP)
pH water
Ca
Mg
OC %
OM %
Phosphore Assimilable (ppm) Bray II