Abstract
Rock fines from basalt, trachyte and volcanic pyroclastic materials in
addition to limestone and gneiss were applied as fertilizers on tropical
soils in several localities in west Cameroon. After harvesting, soil
samples from controls and different treatments were collected and
analyzed to assess the variation of textures and soil chemical
compositions. Cabbage and potatoes as the test crops treated under fines
from volcanic pyroclastic materials and basalt yielded the highest and
lowest productivities, respectively. The initial loamy sand of the
controls moves towards clay textures while initial clay textures
remained unchanged, suggesting a loss of sand proportion and an increase
in clay particles. For the pH, the slightly, moderately to strongly
acidic properties of the local soils (4.8 ≤ pH ≤ 6.5) were shifted
upwards in between the slightly acidic and the slightly alkaline soils
(6.6 ≤ pH ≤ 7.2). However, a sample treated with fines from pyroclastic
materials showed a remarkable pH increase from 5.9 to 6.9. The trends of
fluctuation of organic carbon and organic matter are parallel with a
general increase of these chemicals in soils. Na and K remains constant
with a general increase trend for Mg and Ca in most treatments. The
highest available phosphorus content of 96.0 ppm was found on the
treatment with trachyte fines; followed by 50.9 and 51.5 ppm encountered
on treatments with limestone and basalt fines, respectively. Then, this
suggests a significant increase of phosphorus in soil after treatments
with some rock fines such as trachyte, limestone, gneiss and basalt.
Keywords: yield; rock fines; soil chemicals; soil physico-texture; soil
pH and Phosphorus
INTRODUCTION
Soil erosion is a process acting over millions of years. It is known as
“geologic” or natural when caused by factors such as climate, soil
type and topography, according to Bennett and Chapline (1928). Human
also induced soil erosion through activities such as overgrazing,
deforestation and agriculture which are the major factors of the soil
erosion accounting for 92 % of all activities destroying the soil
structure (Mostafa and Osama, 1992). Then, soil erosion is a leading
cause of soil infertility with a detrimental impact on the agricultural
productivity. In fact, soil productivity depends on a number of
physical, chemical, biological and soil properties. The chemical
fertility depends on the amount of available nutrients in a soil which
is governed by the soil pH, organic matter content and other
characteristics. Then, soil erosion leads to the decrease of the
chemical fertility through the leaching of some nutrients and the loss
of agricultural productivity. This also leads to the economic damage of
the income of farmers with alarming damage 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 to solve the problem of soil depletion
in chemicals in sub-Sahara Africa. This work focuses on an alternative
to the use of chemical fertilizers to combat chemical loss in soils.
This method is based on the application of fines from different types of
rocks to increase chemicals in soils.
METHODOLOGY
Soil samples were collected from 06 different sites namely Befang
(06°20’18”N, 10°02’47”E), Foumbot (05°32’25”N, 10°35’30”E), Batibo
(05°45’10”N, 09°45’35”E), Santa (05°47’58”N, 10°09’46”E) Kalong
(04°47’30”N, 11°03’53”E) and Bonadale (04°09”36”N, 09°34’34”E) located
in west, centre and littoral regions of Cameroon (Table 1). Each site is
represented by an experimental plot made up of a control and treated
soils replicated three times when growing a test crop. The test crops
were chosen based on its growth capacity on a specific site. They were
mostly made up of maize (Zea mays ). However cabbage
(Brassica oleracea ), carrots (Daucas carota ) and Irish
potatoes (Solanum tuberosum ) were also used as test crops in some
sites. Then, fresh rock samples locally collected were crushed into
smaller fragments then pulverized several times into fines and sieved
with a 1x1mm mesh sieve and used as fertilizers. The rocks used as fines
are volcanic such as basalt, trachyte and volcanic pyroclastic materials
in addition to gneiss and limestone. Fines of dried Tithonia
Diversifolia was also used as green manure. Poultry manure or cow dump
were also added to some treatments.
After harvesting and yields determined for each crop, soil samples were
collected from all the controls and treated soils on 06 different spots
of each plot unit and within 0- 25cm of depth, mixed, dried and stored
in clean plastic bags and taken for further description and analysis in
the Laboratory of Soil Sciences, Faculty of Agronomy, University of
Dschang, Cameroon. In the laboratory, soil samples were air-dried at
room temperature for one week and passed through a 2-mm polyethylene
sieve to remove plant debris and pebbles. Afterwards, they were lightly
crushed in an agate mortar into fine powder and passed through a
0.149-mm nylon sieve then stored in glass containers then preserved
under ambient conditions pending analysis. The soil samples were
subjected to physiological analysis using a standard laboratory
procedure for soil analyses (AFNOR). Soil reaction was determined in
soil water suspension 1:2.5 using a glass electrode. Organic matter was
determined by wet digestion according to Walkley and Black (1934). Total
nitrogen was analyzed by the method of Kjeldahl (1883) modified.
Exchangeable cations and exchange capacity (CEC) were determined by
percolation with 1 M ammonium acetate, and the determination of Ca, Mg,
K and Na using a flame photometer and Mg with an atomic absorption
spectrophotometer. And pHwater (Peech, 1965) was
measured with a pH meter at 1:2.5 soil/water.
RESULTS
The results are made up of the yields of each test crops (Table 1) in
addition to the textures and chemical compositions of control and
treated soils (Table 2 and Table 2 (continued)). The texture was
determined based on the percentage composition of each soil sample in
sand, silt and clay. Parameters such as pH, OM and OC (%), N (g/Kg),
Ca, Mg, Na and K (meq/100 g) and P (ppm) were determined as chemical
compositions for the control and treated soils. The variations in
chemical contents between controls and treated soils were determined to
appraise chemicals’contents in soils after treatments.
Yields
Maize was used as the test crop in the localities of Foumbot, Bonandale
and Kalong. However cabbage, carrots and potatoes were also used in
Befang, Santa and Batibo, respectively.
Maize as the test crops yielded (after 03 months of growth) 833, 3200
and 4000 Kg/ha for the controls T01, T02 and T03 in the localities of
Foumbot, Bonandale and Kalong, which are made up of basalt, sediments
and gneiss as country rocks, respectively. Out of the different treated
soils where maize was used as the test crop, the best yield was obtained
from T23 (= T03 + 3Kg gneiss fines) in the locality of Kalong. This is
followed by higher yields of 8300 and 8000 Kg/ha obtained on T22 (= T02
+ 2Kg limestone fines) and T13 (= T03 + 3Kg basalt fines) in Bonandale
and Kalong, respectively. Yields as low as 5400 and 3200 Kg/ha were
obtained on treatments T12 (= T02 + 2Kg basalt fines) and T62 (= T02 +
1Kg limestone fines) in the same locality (Bonandale). The lowest yield
comes from T41 (= T01 + 600g basalt fines + 600g poultry manure)
cultivated in Foumbot.
Cabbage yielded productivities as high as 15 000 and 11 6666Kg/ha for
treatments T24 (= T04 + 200g fines from pyroclastic bombs) and T44 (=
T04 + 200g fines from less vesicular pyroclastic materials),
respectively. However, the lowest yield of 2444Kg/ha was obtained from
the control soil (T04). Intermediate yields of 3578 and 6444Kg/ha were
obtained with T14 (= T04 + 200g lapilli fines) and T34 (= T04 + 200g
fines from highly vesicular pyroclastic materials), respectively. More
details on this work are found in Tetsopgang and Konyuy (2019).
The highest yield of carrots with the value of 925Kg/ha was obtained
from treatment T35 (= T05 + 1kg basalt fines + 10ml LMO + 0.5Kg
Tithonia). Lower yields of 525, 506 and 150Kg/ha were obtained from
treatments T45 (= T05 + 1Kg basalt fines + 0.5Kg Tithonia), T25 (= T05 +
1Kg basalt fines + 10 ml LMO) and T15 (=T05 + 1Kg basalt fines),
respectively. The control (T05) yielded intermediate productivity with
500Kg/ha. The highest yield of potatoes was from T26 (= T06 + 2Kg basalt
fines + 2Kg coal fines) with 20 741Kg/ha, followed by the control (T06)
with 14 816Kg/ha. The lowest yield is found on treatment T46 (= T06 +
2Kg trachyte fines +2Kg coal fines) with 13 333Kg/ha.
The performance index (Yi = Yield per treatment/Yield per control)
indicates the number of folds increase of each treatment in relation to
its control. The higher performances Yi (= 6.13 and 4.77) are found in
the locality of Befang with treatments T24 and T44, respectively. This
locality also portrayed another high Yi (= 2.63) for treatment T34.
Other performances as high as 3, 2.75, 2.59 and 2 are found in
treatments T41, T23 and T22 in the localities of Foumbot, Kalong and
Bonendale. Other performances are 1 ≤ Yi ≤ 2 and found sparse in all
localities subject to this study. However, the localities of Santa and
Batibo showed that treatments T15 and T46 yielded less than their
controls with Yi (= 0.30 and 0.89), respectively
Texture and Chemicals
Control soils
The control soils show textures of loamy sand (T01 and T02) to clay
(T03) passing through clay loam (T06) and silty clay (T05). The highest
pH values (= 7.10 and 6.40) were observed on loamy sandy samples (T01
and T02, respectively). The lowest pH (= 4.60) is portrayed by the silty
clayish sample (T05). Intermediate pH values (= 5.92, 5.80 and 5.60)
were observed on samples T04, T06 and T03 with clayish affinity. For the
organic matters (CO, MO and N), the highest values of CO and MO (= 6.39
and 11.29 %, respectively) were observed on the control T06 collected
on a clayish soil in Batibo (Table 2). Samples T03 and T02 show lowest
values (= 0.95 and 1.30 %) of CO and MO. Intermediate values of CO and
MO (= 2.30; 3.81 and 4.00; 6.57 %) came from samples T04 and T05,
respectively. N also exhibits higher values (= 4.62 and 3.06) on T01 and
T05, respectively. Lower values (= 0.06, 0.56 and 0.16) were found on
T03, T02 and T06. For the exchangeable cations (Ca, Mg, K and Na), Ca
exhibits highest values (= 3.84 meq/100g) while lowest values belong to
Na and K (= 0.01 meq/100g). K and Mg exhibit values between 3.2 –
0.01meq/100g. The strongest capacity of cationic exchange belongs to T04
and T06 with values of 22.00 and 20.40. Available phosphorus (P) values
are between 26.5 and 6.8 ppm for these controls.
Treated soils
The textures of most treated soils fall in the field of sandy loam (T12,
T22, T12B, T22B) and clay (T62, T62B, T13, T23 and T45). However, some
treated samples presented properties of clay loam (T26 and T46) and
laomy sand (T41). This sample exhibits the highest pH (= 7.2) while the
lowest pH (= 4.8) belong to T15 and T45. For CO, the highest values (=
7.03, 6.80 and 6.74 %) were encountered on samples T26, T24 and T46,
respectively (Table 2). Values of CO as low as 0.21 and 0.34 % were
observed on samples T12 and T22, respectively. In fact, most samples
show intermediate CO values with values within 1.13 and 6.39 %. Treated
soils with lowest values of CO also show lowest MO which are 0.35 and
0.59% for samples T12 and T22, respectively. Samples (T26, T46 and T41)
with highest CO also portrayed highest values of MO (= 12.12, 11.62.
11.29%), respectively. N portrays the highest concentration (= 5.46
g/Kg) on T41 followed by lower values (= 3.06, 2.92 and 2.91)
encountered on T25, T35 and T15, respectively. For the exchangeable
cations (Ca, Mg, K and Na), Mg exhibits the highest values (= 45.76 and
24.00 meq/100g) belonging to T26 and T46. These samples also present
higher values of Ca (= 10.24 and 3.20 meq/100g), However samples T13 and
T23 also present higher values (= 6.64 and 9.12 meq/100g, respectively)
for Ca and Mg (= 3.67 and 4.26 meq/100g, respectively). Then the sum of
exchangeable cations are higher on samples T26 (=56.00 meq/100g), T46 (=
27.20 meq/100g), T23 (=14.13 meq/100g) and T13 (= 11.08 meq/100g). The
lowest values of exchangeable cations (= 0.1 - 0.0 meq/100g) are those
of Na. K also exhibits low values (= 1.08 – 0.0). The strongest and the
weakest capacity of cationic exchangeable (= 48.89 and 8.8 meq/100g,
respectively) were found on T23 and T25, T35, T45 and T41, respectively.
For the available phosphorus (P), the highest value (= 95.96 ppm) was
found on sample T46. Samples T22B and T12B also present higher values of
71.37 and 75.80 ppm, respectively. Values as high as 51.50, 50.91 ppm
were observed with samples T22 and T62. Other higher values of P are
encountered on T23, T24, T44, T13, T12, T34, T26, T15 and T14 with
32.70, 30.11, 28.25, 27.95, 26.65, 26.38, 24.30, 23.56 and 21.49 ppm,
respectively. Intermediate values are between 7.24 and 18.45 ppm and
2.07 ppm is the lowest values of P found on T62B (Table 2) and (Table
(continued)).
The variation of pH and the concentrations of various chemicals between
values of different controls and those of corresponding treated soils
are presented in Table 3. The highest positive pH variation (∆pH = +
0.98) was encountered on sample T24 (= T04 + 200g fines from volcanic
pyroclastic materials). This sample also exhibits the highest OC and OM
variations (∆OC = 4.50 and ∆OM = 5.11), respectively. A positive ∆pH as
high as + 0.80 was observed on a couple of samples, T44 (= T04 + 200g
fines from less vesicular pyroclastic materials) and T23 (= T03 + 3Kg
gneiss fines). This couple of samples, T44 and T23 also show higher ∆OC
(= + 3.30 and = + 1.11) and ∆OM (= + 3.10 and = + 2.48), respectively.
Samples T26 (= T06 + 2Kg basalt fines + 0.75Kg green manure) and T12 (=
T02 + 2Kg basalt fines) both exhibit negative pH variations (= – 0.60
and = – 0.40), corresponding to negative ∆OC (= - 0.19 and - 1.09) and
∆OM (= - 0.33 and - 1.89), respectively. The highest ∆N (+ 0.84) belongs
to sample T41 with manure in his composition.
Most exchangeable cations exhibit low variations with - 0.73 ≤ ∆K ≤
0.38, - 0.02 ≤ ∆Na ≤ 0.75, - 1.48 ≤ ∆Ca ≤ 2.80 and – 0.76 ≤ ∆Mg ≤ 1.99.
However some higher variations of ∆Ca and ∆Mg are encountered for a
couple of samples T23 (= 5.28 and 1.99) and T26 (= 7.04 and 52.56),
respectively. ∆Mg is also higher for T46 (= 20.80). The most remarkable
variation of chemical concentrations were found on phosphorus contents.
Although negative variations are observed on T45 (= – 2.07), T25 (= -
2.62), T62B (= -5.71) and T25 (= -6.70), other samples such as T12, T22,
T62, T22B, T12B and T46 exhibit positive phosphorus variations with
values as high as 18.87, 43.72, 43.13. 63.59, 68.02 and 76.83,
respectively. Positive and low phosphorus contents between 0.42 and 8.65
are observed on samples T41, T13, T23, T14, T34, T15, T26 and T44 (Table
3).
DISCUSSION
The texture and physico-chemical properties of soils treated with fines
from different rock types ± manure were assessed in several localities
of Cameroon. There is general variation of textures and physico-chemical
parameters of treated soils in relation to the controls: the initial
loamy sand texture of the controls moves to sandy loam and clay laom
textures; sandy clay texture moves to clay texture and initial clay
textures remained unchanged. This suggests that a soil treated with rock
fines ± manure losses sand proportion while increasing mostly in clay
and somehow in silt particles. In respect to the pH, the slightly,
moderately to strongly acidic properties of the local soils were shifted
upwards in between the slightly acidic and the slightly alkaline soils
(Figure 1). This suggests a general increase of pHs after treatments.
For example, in the locality of Santa, a pH (= 4.60) of a control T05
increases to pH (= 4.80 and = 4.90) corresponding to treated soils T15,
T45 and T25, T35, respectively. In fact, there is a general positive
increase of pHs between +0.10 and +0.98) (Table 3). However, a couple of
samples exhibit negative pH variations (∆pH = - 40 and ∆pH = - 60) on
samples T12 (= T02 + 2Kg basalt fines) and T26 (= T06 + 2Kg basalt fines
+ 2Kg caol fines) in the locality of Bonandale and Batibo, respectively.
This implies the potential of these treatments to increase or decrease
soil pHs. The organic carbon (OC) and organic matter (OM) also showed
variations after the application of different treatments. The trends of
fluctuation of OM and OC are parallel throughout all control and treated
soils (Figure 2). Some samples exhibit positive ∆OM and ∆OC while other
show negative ∆OM and ∆OC (Table 3). This implies that these soils
showed increasing or decreasing OC and OM after treated with rock fines
± manure. The highest values of ∆OM (= + 5.11) and ∆OC (= + 4.50) were
found on sample T24 (= T04 + 200g fines from pyroclastic bombs) which
also showed the highest ∆pH (= + 0.98) and yield index (Yi= 6.13). The
second highest Yi (= 4.77) from the sample T44 (= T04 + 200g fines from
less vesicular pyroclastic bombs) also exhibit higher ∆pH (= +0.80), ∆OM
(= + 3.10) and ∆OC (= +3.30). This suggests that fines from pyroclastic
materials increase pH, OM and OC contents in different treatments. This
is also observed on treatments with fines from basalt. However negative
∆pH is observed on samples T12 and T26 which were treated with fines
from basalt. These samples also showed negative ∆OM and ∆OC. This
suggests that a decrease of pH implies as decrease in OM and OC.
Regarding other soil nutriments, N contents remained very weak ≤
1.00g/Kg except some higher values between 2.77 and 3.06 g/Kg
encountered for sample T15, T25, T35 and T45. These samples were treated
with basalt fines + green manure. Then, added N may come from the
manure. 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 4). 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
Fines from different rock types such as basalt, trachyte, volcanic
pyroclastic materials in addition to limestone and gneiss applied as
fertilizers, indicate a slight increase of pH in all samples in several
localities in Cameroon. However there is a remarkable pH increase in a
treatment with basalt fines. Then the application of the fines from
basaltic rocks may be used to manage the soil acidity. These basalt
fines also increase significantly the soil contents in MO, CO, Mg and
Ca. There is a good and parallel correlation of MO and CO contents in
all treated soils. The higher values of P suggests the application of
these rock fines as good potential sources of phosphorus in tropical
soils.