Up to date, tropical mountainous ecosystems still lack in depth information on soil and environmental characteristics which are major factors limiting optimum crop production. The objective of this work was to study soil characteristics and to evaluate the land capability level for the production of some common tropical crops in mountainous ecosystem soils of North West Cameroon. Soil sampling was done following a randomized complete block design (RCBD) with four replications for three topographic positions (upslope, midslope and footslope) and at two depths (0 - 20 cm and 20 - 100 cm). It was completed by standard laboratory analyses. The fertility capability classification (FCC) system enabled to identify soil limitations and to classify soils into FCC units. Land and climate were evaluated by simple limitation and parametric methods. Globally, the soils were dark-colored, sandy clayey to clayey, compact and very acidic (pHH 2O = 4.3 - 5.8). The organic matter (3.7% - 5.1% dry matter), total nitrogen (0.08% - 0.56%) and available phosphorus (22.1 to 30.9 mg⋅kg −1) recorded for the 0 - 20 cm depth then reduced with depth but midslope values were also lower. The C/N ratio varied between 9 and 45. Low C/N values appeared mostly in 0 - 20 cm depth at the upslope and downslope soils and subsurface soils of midslope position. Exchangeable Ca was very low to low (1.43 - 3.6 cmol + kg −1), Mg was very low to low (0.39 - 1.5 cmol + kg −1), K was low to medium (0.2 - 0.54 cmol + kg −1) and Na was very low (<0.1 cmol + kg −1). The sum of exchangeable bases was very low (3.02 - 5.19 cmol + kg −1), cation exchange capacity was low to moderate (8.60 - 25.6 cmol + kg −1) and base saturation was very low to low (19.27% - 36.97%). Leaching of bases under heavy rainfall is a major cause of soil acidification under humid topical ecosystems. The Ca/Mg/K ratio was unbalanced and Mg was the most relatively concentrated base in all the soils. There was a clear variation of most of the soil properties along the slope and with depth. The soils were classified in the FCC system as aek for the upslope soils, Caek for the midslope soils and Cagk for the footslope soils. The principal limitations to production of huckleberry, beans, maize and potatoes were heavy rainfall, wetness, steep slope, soil texture/structure and low soil fertility. These constraints might be overcome by farming at the end of the raining season, contour ploughing, terracing, fertilization and liming.
Mountainous ecosystems are quite widespread in the intertropical zone [
Bafut Sub-Division covers an area of about 340 km2. It is situated about 20 km northwest of Bamenda town (north of Mezam Division, North West Region) between latitude 06˚05'N - 06˚11'N and longitude 09˚58'E - 10˚11'E (
annual temperature is 22.3˚C [
Thus, red ferrallitic soils occur in the southern high plateaus. In the north, most of the hill slopes are covered by brunified soils; alluvial soils are abundant in the Mezam river valley. Hydromorphic soils are common in the swampy valleys [
Based on several soil surveys, supported by a reconnaissance of the studied area, about twenty soil profiles representative of the area were studied through boreholes. The three most representative profiles were selected at upslope, midslope and footslope following a NE-SW transect (
Samples from each horizon were mixed together to obtain a composite sample per horizon per sub-plot. Altogether, two composite soil samples were obtained for each plot making a total number of six samples from the three topographic positions. After collection, samples were stored in clean plastic bags and conveyed to the laboratory for further processing and analysis. In the laboratory, the 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 to fine powder and passed through 0.149-mm nylon sieve. The physico-chemical analyses of soils were done at the “Laboratoire d’Analyses des Sols et de Chimie d’Environnement
Site characteristics | Upslope | Midslope | Footslope |
---|---|---|---|
Altitude (m) | 1300 | 1160 | 1000 |
Precipitation (mm) | 2657.2 mm | 2657.2 mm | 2657.2 mm |
Mean annual air temperature (˚C) | 23.4 | 24 | 24.7 |
Mean annual soil temperature (˚C) | 21 | 21.6 | 22.3 |
Vegetation | Grassed savannah | Grassed savannah with stunted trees | Grassed savannah with raffia |
Slope gradient in % (class) | 2 (Very gentle). | 10 (steep) | <1 (sub-horizontal) |
Parent rock | Basalt | Basalt | Basalt, colluvium |
Soil type | Red ferrallitic soil | Red ferrallitic soil | Hydromorphic soil |
Soil use | Farming | Farming | Farming |
(LABASCE)” of the Faculty of Agronomy and Agricultural Sciences (University of Dschang, Cameroon). The soil relative humidity was determined by noting the weight-loss of an air-dried sample, after subjecting it to an oven temperature of 105˚C for 24 hours [
m = A l A l + S × 100
The structural stability index (SI) was obtained using the following equation [
S I = 1.724 O C ( silt + clay ) × 100 ; 0 ≤ S I ≤ ∞
The slaking index (Is) was estimated from the following formula for acid soils [
I s = 1.5 L f + 0.75 L g C + 10 O M − 0.2 ( p H − 7 )
where Lf is % fine silt, Lg is % coarse silt, Cl is % clay and OM is % organic matter.
Version 4 (
The land and climatic parameters limiting the growth and production of major crops in the area (huckleberry, maize, beans and groundnut) were evaluated by simple limitation and parametric methods of [
The soil morphological characteristics are summarized in
Soil characteristics | Upslope | Midslope | footslope | ||||
---|---|---|---|---|---|---|---|
Ap (0 - 20 cm) | A1 (20 - 100 cm) | Ap (0 - 20 cm) | A1 (20 - 100 cm) | Ap (0 - 20 cm) | A1 (20 - 100 cm) | ||
Colour (moist) | Code | 7.5YR3/3 | 10R3/6 | 5YR3/4 | 10R3/6 | 7.5YR4/1 | 7.5YR4/1 |
Color | Dark brown | Dark yellowish brown | Dark brown | Dark yellowish brown | Dark grey | Dark grey | |
Structure | Vf, l & m | m | Vf, l & m | m | f, m & s | m | |
Consistency | Dry | s | h | s | h | s | h |
Wet | s & p | s & p | s & p | s & p | s & p | s & p | |
Rock fragments | n | n | n | n | n | n | |
Roots | c, f | f, f | c, f | f, f | c, f | f, f |
Structure | Consistency | Rock fragments | Roots | ||||
---|---|---|---|---|---|---|---|
Size | Type | Grade | Dry | wet | Abundance | Thickness | |
vf = very fine (<5 mm) f = fine (5 - 10 mm) m = medium (10 - 20 mm) c = coarse (20 - 50 mm) vc = very coarse (>50 mm) 1 = weak; 2 = moderate; 3 = strong; | g = granular ab = angular blocky sb = subangular blocky l = lumpy m = massive | w = weak (peds barely observable) m = moderate (peds observable) s = strong (peds clearly observable) | l = loose s = soft h = hard | s = sticky p = plastic | n = none (0%) v = very few (0% - 2%) c = common (5% - 15%) m = many (15% - 40%) a = abundant (40% - 80%) d = dominant (>80%) | f = few; c = common | f = fine; m = medium |
yellowish brown colour, while the downslope soils were dark grey at surface and subsurface. The structure was very fine, lumpy and massive at the surface to massive at depth. The surface horizons were soft and friable when dry but soft and plastic under wet conditions; meanwhile the subsurface horizons were hard when dry but soft and plastic when wet. Rock fragments were absent while plant roots were fine and common in the bottom horizons but fine and few at subsurface. Similar soils have already been described in the Bambouto Mountains of Western Cameroon and were classified as andic ferrallitic soils [
The studied soil physico-chemical characteristics are presented in
Soil Characteristics | Upslope | Midslope | Footslope | |||
---|---|---|---|---|---|---|
Ap (0 - 20 cm) | A1 20 - 100 cm) | Ap (0 - 20 cm) | A1 (20 - 100 cm) | Ap (0 - 20 cm) | A1 (20 - 100 cm) | |
Moisture content (105˚C) | 16.3 | 18.42 | 8.20 | 16.21 | 15.80 | 15.21 |
Particle density (g・cm−3) | 2.6 | 2.6 | 2.6 | 2.6 | 2.6 | 2.6 |
Bulk density (g・cm−3) | 1.7 | 1.8 | 1.5 | 1.7 | 1.7 | 1.7 |
Porosity (%) | 34.6 | 30.76 | 42.3 | 34.6 | 34.6 | 34.6 |
Texture | 55 | 48 | 23 | 32 | 26 | 31 |
10 | 12 | 34 | 17 | 20 | 21 | |
35 | 40 | 43 | 51 | 54 | 48 | |
Sandy clay | Sandy clay | Clay | Clay | Heavy clay | Clay | |
pH (H2O) | 4.3 | 5.3 | 4.4 | 5.2 | 4.6 | 5.8 |
pH (KCl) | 4.0 | 4.9 | 4.3 | 4.9 | 4.4 | 5.4 |
ΔpH | 0.3 | 0.4 | 0.1 | 0.3 | 0.2 | 0.4 |
Organic carbon (% dry matter) | 4.8 | 0.79 | 3.7 | 0.46 | 5.1 | 1.86 |
Organic matter (%) | 8.3 | 1.36 | 6.36 | 0.79 | 8.9 | 3.21 |
Total nitrogen (% dry matter) | 0.42 | 0.03 | 0.08 | 0.04 | 0.56 | 0.12 |
Exchangeable cations (cmol + kg−1) | 1.6 | 1.99 | 1.9 | 1.43 | 3.6 | 2.11 |
1.40 | 0.87 | 1.12 | 1.02 | 1.5 | 0.39 | |
0.2 | 0.13 | 0.16 | 0.25 | 0.29 | 0.54 | |
0.08 | 0.06 | - | 0.01 | 0.10 | 0.06 | |
Sum of exchangeable bases (cmol + kg−1) | 5.19 | 3.02 | 3.18 | 2.71 | 5.49 | 3.1 |
CEC at pH7 (cmol + kg−1) | 20.9 | 8.6 | 16.05 | 8.11 | 25.6 | 12.08 |
Apparent CEC (CECapp) (cmol + kg−1) | 13.14 | 14.7 | 8.79 | 12.80 | 14.44 | 11.79 |
Available phosphorus (ppm) | 30.9 | 7.01 | 22.1 | 5.11 | 27.06 | 3.97 |
Exchangeable Al (cmol + kg−1) | 1.85 | 0.79 | 0.56 | 0.26 | 1.59 | 0.21 |
Al toxicity (%) | 26.27 | 20.73 | 14.97 | 8.75 | 22.45 | 6.34 |
ranged from sandy clayey at the upslope to clayey at the midslope and heavy clayey at the footslope. The gravel content was low, due probably to the volcanic nature of the parent material which undergoes intense weathering under humid tropical climate favourable to leaching and the uneven and aggressive nature of the relief that promote excellent drainage and erosion [
The soil nutrient ratios and fertility indices (
Fertility parameter | Upslope | Midslope | Footslope | |||
---|---|---|---|---|---|---|
Ap (0 - 20 cm) | A1 20 - 100 cm) | Ap (0 - 20 cm) | A1 (20 - 100 cm) | Ap (0 - 20 cm) | A1 (20 - 100 cm) | |
SSI | 18.44 | 2.62 | 8.26 | 1.16 | 12.03 | 4.65 |
Slaking index | 0.21 | 0.23 | 0.55 | 0.43 | 0.64 | 0.48 |
Silt/clay ratio | 0.28 | 0.30 | 0.79 | 0.33 | 0.37 | 0.44 |
C/N ratio | 11.42 | 26.33 | 46.25 | 11.50 | 9.11 | 15.5 |
TN/pH ratio | 0.01 | 0.01 | 0.02 | 0.01 | 0.12 | 0.02 |
N/P ratio | 13.59 | 0.43 | 3.62 | 0.78 | 20.69 | 30.23 |
C/P ratio | 1553.39 | 1114.25 | 1674.21 | 900.20 | 1884.7 | 4687.14 |
Ca/Mg ratio | 1.14 | 2.29 | 1.70 | 1.40 | 2.40 | 5.41 |
Mg/K ratio | 7 | 6.69 | 7 | 4.08 | 5.17 | 0.72 |
ESP (%) | 0.72 | 0.29 | - | 0.12 | 0.39 | 0.49 |
S/CEC pH7 (%) | 24 .83 | 36.97 | 19.27 | 27.07 | 21.44 | 25.66 |
Ca/Mg/K ratio | 50/43.75/6.25 | 66.6/29.01/4.34 | 59.74/35.22/5.03 | 52.96/37.78/9.26 | 66.75/27.83/5.38 | 69.40/12.82/17.78 |
CRC | 0.66/2.43*/1.04 | 0.86/1.62*/0.72 | 0.79/1.95*/0.84 | 0.69/2.09*/1.54* | 8.88/1.56*/0.89 | 0.91/0.71/2.96* |
F | 0.18 | 0.19 | 0.17 | 0.21 | 0.46 | 0.34 |
CECapp/Clay ratio | 0.36 | 0.37 | 0.79 | 0.25 | 0.26 | 0.25 |
CRC: coefficient of relative concentration; ESP: Exchangeable sodium percentage; F: Forestier’s index (S2/(Clay + fine silt)); SSI: Structural stability index.
lowest ones at upslope. Apart from the footslope positions, all the other landscape positions showed a Ca/Mg ratio of less than 2 suggesting a cationic imbalance between Mg and Ca [
0.68 (
The major constraints of the upslope soils to crop production were aluminum toxicity, high leaching potential, low nutrient capital reserve (
Categorical levels | Upslope | Midslope | Footslope | |
---|---|---|---|---|
Type | − | C | C | |
Substrata type | − | − | − | |
Modifiers | a | + | + | + |
b | − | − | - | |
e | + | + | - | |
g | − | − | + | |
k | + | + | + | |
m | + | + | + | |
FCC | aek | Caek | Cagk |
C: clay; a: aluminium toxicity; b: basic reaction; e: high leaching potential; g: waterlogging; k: low nutrient capital reserve; m: organic matter depletion; v: vertic properties; +: greater expression of the modifier; −: lesser expression of the modifier.
The fertility status of these soils was studied through land evaluation using simple limitation and parametric methods [
Landscape, soil and climatic characteristic | Upslope | Midslope | footslope | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Groundnut | huckleberry | Maize | beans | Groundnut | huckleberry | Maize | beans | Groundnut | huckleberry | Maize | beans | |
Climate (c) | ||||||||||||
Precipitation during crop cycle (mm) | S1-1 | S1-1 | S1-1 | S1-0 | S1-1 | S1-1 | S1-1 | S1-0 | S1-1 | S1-1 | S1-1 | S1-1 |
Mean T˚C during crop cycle (˚C) | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 | S1-1 |
Annual Precipitation (mm) | N2 | N2 | S3 | S3 | N2 | N2 | S3 | S3 | S3 | N2 | N2 | S3 |
Topography (t) | ||||||||||||
slope | S1-0 | S1-0 | S1-0 | S1-0 | S2 | S1-1 | S1-1 | S2 | S1-0 | S1-0 | S1-0 | S1-0 |
Wetness (w) | ||||||||||||
Flooding | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | N2 | N2 | N2 | N2 |
drainage | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | N2 | N2 | N2 | N2 |
Soil physical characteristics (s) | ||||||||||||
Texture/structure | S1-1 | S1-1 | S1-1 | S1-1 | S1-0 | S1-1 | N2 | N2 | S2 | S1-1 | N2 | N2 |
Course fragments (%) | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 |
Soil depth (cm) | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 |
Soil fertility (f) | ||||||||||||
S (cmol + kg−1) | S1-0 | S1-0 | S1-0 | S1-0 | S2 | S2 | S2 | S2 | S1-0 | S1-0 | S1-0 | S1-0 |
CECapp (cmol + kg−1) | S1-1 | S2 | S2 | S2 | S1-1 | S2 | S2 | S2 | S1-1 | S2 | S2 | S2 |
Base saturation (%) | S2 | S2 | S2 | S2 | S2 | S2 | S2 | S2 | S2 | S2 | S2 | S2 |
pH (H2O) | N2 | N2 | N2 | N2 | N2 | N2 | N2 | N2 | N2 | N2 | N2 | N2 |
OC (%) | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 |
Salinity (n) | ||||||||||||
ESP (%) | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 | S1-0 |
Suitability | ||||||||||||
Class | S2fN2cf | S2fN2cf | S2fS3cN2f | S2fN2f | S2fN2cf | S2fN2cf | S2fN2csf | S2ftS3cN2sf | S2sfS3cN2wf | S2fS3cN2cwf | S2fNwsf | S2fS3cN2wf |
S1-0: no limitation, very suitable, optimal yield (95% - 100%); S1-1: slight limitation, suitable, almost optimal yield (85% - 95%); S2: moderate limitation, moderately suitable, acceptable yield (60% - 85%); S3: severe limitation, marginally suitable, low yield (85% - 95%); N1: very severe limitation, not recommended, but potentially suitable, unacceptable, very low yield (25% - 40%); N2: very severe limitation, not recommended, potentially not suitable, unacceptable yield (0% - 25%).
yields (0% - 25%). These results are consistent with those already documented by [
Quantification of nutritional deficiencies in soils requires raising the base saturation to 50% (adequate for the growth of most plants according to [
The objective of this work was to study the major characteristics of some mountainous soils in the North-western Highlands of Cameroon and to evaluate their potentials for the production of some common tropical crops. The principal results revealed that those soils are dark-coloured with a sandy clayey to clayey texture, a very high compacity and a very acidic reaction. The organic matter, total nitrogen, available phosphorus and C/N ratio were mainly high at the surface. All the exchangeable bases were low in relation to leaching processes that dominate mountainous landscapes. Leaching of bases under high rainfall conditions might be responsible for the acidic reaction of those soils. The sum of exchangeable bases (S), cation exchange capacity (CEC) and base saturation were
low at the upslope and midslope but modest at the footslope position. The Ca/Mg/K ratio was imbalance relative to the ideal equilibrium condition of 76/18/6 and Mg was the most relatively concentrated exchangeable base. There was a clear variation of most of the soil properties along the slope and with depth. The soils were classified in the FCC system as aek for the upslope soils, Caek for the midslope soils and Cagkm for the footslope soils in FCC system. The principal limitations to the production of huckleberry, bean, maize and potatoes in Bafut were heavy rainfall, wetness, steep slope, soil texture/structure and soil fertility decline. These constraints might be overcome by cultivation of such crops at the end of the raining season, contour ploughing, terracing, fertilization and liming.
The authors declare no conflict of interests.
Azinwi Tamfuh, P., Temgoua, E., Wotchoko P., Boukong, A. and Bitom D. (2018) Soil Properties and Land Capability Evaluation in a Mountainous Ecosystem of North-West Cameroon. Journal of Geoscience and Environment Protection, 6, 15-33. https://doi.org/10.4236/gep.2018.67002