Chemical properties of wild coffee forest soils in Ethiopia and management implications

doi:10.4236/as.2011.24057

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Vol.2, No.4, 443-450 (2011)

doi:10.4236/as.2011.24057

Agricultural Scienc es

Chemical properties of wild coffee forest soils in

Ethiopia and management implications

Taye Kufa

Ethiopian Institute of Agricultural Research, Jimma Research Center, Jimma, Ethiopia; [email protected]

Received 7 September 2011; revised 19 October 2011; accepted 27 October 2011.

ABSTRACT

The study aims at determining the status of soil

chemical fertility in four wild coffee forests of

southeast ern and southw estern Eth iopia. Acc ord-

ingly, soil samples were collected from surface

and subsurface depths at three sites w ithin each

forest and analy zed for soil chemical properties.

The results depicted that the soils at the four

coffee forests did not reveal significant varia-

tions for most parameters, except Mg, CEC and

C:N ratio. Significant variations w ere determined

between the surface and sub-surface soils of

the four studied forests, partly indicating the

impacts of anthropogenic factors on vegetation

cover and soil fertility status along profile depth.

At Harenn a, surfa ce so il had si gnifica ntly hi gher

total nitrogen and organic matter than sub-surface

soil. The decline in available phosphorus with

soil depth was also significant at the Harenna

and Yayu forests. Most soil results were com-

parable and showed inter- an d in tra -fo rest varia-

tions, demonstrating the contributions of vege-

tation cover and climate gradients. The study

revealed the declined soil quality parameters

with increased depth, demonstrating the vul-

nerability of forest soils to human-induced dis-

turbances of natural habitats and land degrada-

tion, coupled with climate changes. Overall, the

results underline the need for a multi-site forest

conservation and promote productivity of high

quality coffee standards. This demands urgent

supports for implementing community-oriented

management and incentive options towards main-

taining environmental sustainability and coffee

genetic resources for global benefits.

Keywords: Carbon Sequestration; Coffee Forest

Environments; Profile Depth; Soil Fertility; Wild

Coffee Genetic Resourc es

1. INTRODUCTION

The montane rainforest areas in Ethiopia are the only

known center of origin and genetic diversity for the

highland arabica coffee (Coffea arabica L). In its origi-

nal forest habitat, arabica coffee occurs in the multi-

strata of forest ecosystems and thus it is a shade-loving

plant. Since time immemorial, coffee has been grown in

the humid montane rainforests of southwestern Ethiopia

[1,2]. As to its adaptation, coffee grows in wide ecology

and it does not appear to have very specific soil re-

quirements. In fact, it performs just as well in the clay-

silcaceous soils of granite as it does on soils of volcanic

origin with diverse characteristics or even on alluvial

soils [3,4]. Water-logging can reduce yield by a substan-

tial amount and kill trees if it is prolonged. Texture and

depth of the soil are, therefore, extremely important fac-

tors. Coffee tree is capable of extending its root system

considerably. It requires an effective depth of greater

than 150 cm. This characteristic enables it to exploit a

considerable volume of land and to thus offset a relative

lack of fertility. Highly suitable areas had high soil or-

ganic matter (SOM > 3%) content. With regard to soil

pH, a slightly acid soil is preferred. The best conditions

are between pH 5.3 and 6.5. However, there are also

highly productive coffee plantations on soils that are

nearly neutral (pH = 7.0) [1,4]. Nitrogen is the most im-

portant single element affecting the growth of roots.

However, shoots lack nitrate reductase and thus cannot

utilize nitrate. Phosphorus is an important element in

shoot growth and leaf initiation. Thus, when shoot

growth is more needed than root growth, phosphatic

fertilizers should be applied to encourage faster growth

of suckers [3,5].

In Ethiopia, the natural coffee forest areas, which have

conserved the sustainable ecology and Coffea arabica

gene pools, are now seriously threatened by several fac-

tors. These include, among others, increasing population

pressure, expansion of farmlands, forest land-use con-

flicts, priority for other food and cash crops and other

socio-economic factors [6-9]. There are still natural cof-

T. Kufa / Agricultural Sciences 2 (2011) 443-450

444

fee forests in southwest and southeast Ethiopia with rich

biodiversity including the wild Coffea arabica popula-

tions. The major coffee production systems include for-

est, semi-forest, garden and plantations. The forest eco-

system, which includes coffee forest and semi-coffee

forest production systems, occupies nearly 33% of land

used for coffee production and contributes 25% of na-

tional coffee production. In this regard, the importance

of rainforest conservation can be viewed against the

background of man-made destruction or change in about

60% of the Ethiopian forests during the last thirty years.

This is a serious challenge to the remaining and frag-

mented forest areas (2.6%, about 2000 km2) with wild

coffee populations [8]. Much of the remaining forested

area is located in less accessible and/or relatively less

populated areas of the south and southwest parts of the

country [7]. Management of the inherent good soil

health can enhance sustainable production of high qual-

ity products with little or no external inputs. The ever

increasing demands for forest products and forestlands

together with the growing human population are putting

intolerable pressure on the remaining forest fragments in

Ethiopia and elsewhere. Hence, the increasingly threat-

ened environmental degradation, forest natural resources

and declining soil fertility urgently call for actions be-

fore the status reach irreversible. In view of the chal-

lenges and possible impacts of climate change on envi-

ronmental sustainability, understanding the nature of

soils at each area is important for targeting effective soil

test based amendment options, while maintaining friendly

ecosystems goods and services. Therefore, the study was

carried out to determine the extent of variations in soil

chemical properties along climate gradient and profile

depth in the wild forest coffees of southeastern and

southwestern Ethiopia.

2. MATERIALS AND METHODS

2.1. The Study Area

The study areas are geographically distant and repre-

sent the climate gradients of the remaining fragmented

montane rainforests in southeast and southwest Ethiopia,

hosting the wild arabica coffee genetic resources. These

include Harenna, Bonga, Berhane-Kontir and Yayu. Ex-

cept Harenna in the southeast, the other forests are lo-

cated in the southwest Ethiopia. They are separated by

the Great East African Rift Valley, which dissects the

country into southeast and northwest highlands and rep-

resent climate gradients of Ethiopia. These forests are

fragmented and differ in area coverage (Harenna 15,000

ha, Bonga 5000 ha, Berhane-Kontir 1000 ha and Yayu

1000 ha), physical characteristics and forest vegetation

[7]. The study forests also vary in climate with rainfall

gradients following the decreasing order of Berhane-

Kontir > Yayu > Bonga > Harenna (Table 1).

2.2. Soil Sampling and Laboratory Analyses

Soil samples were collected from three sub-sites within

each montane rainforest. About 500 g soil samples were

collected from two depths: surface (0 - 20 cm) and sub-

surface (20 - 40 cm) for laboratory analyses on the major

soil physico-chemical properties. This was accomplished

between June and July 2004, the main rain season in the

southwest, but the dry season in the southeast Harenna

forest area. The soil samples were air-dried and ground

to pass through a 2 mm sieve for determination of soil

reaction (pH), cation exchange capacity (CEC), ex-

changeable bases (K, Ca, Mg), organic carbon (OC),

total nitrogen (TN) and available phosphorus (AP). The

Table 1. Characteristics of the study wild coffee forests in Ethiopia.

VARIABLE Harenna Bonga Berhane-Kontir Yayu

Wer eda/district Mena-Angetu Gimbo Sheko Yayu-Hurumu

Site code/symbol PI PII PIII PIV

Latitude (N) 6˚23' - 6˚29' 7˚17' - 7˚19' 7˚04' - 7˚07' 8˚23'

Longitude (E) 39˚44' - 39˚45' 36˚03' - 36˚13' 35˚25' - 35˚26' 35˚47'

Altitude (m a.s.l) 1420 - 1490 1520 - 1780 1040 - 1180 1400

Slope (%) 2 - 3 3 - 6 4 - 18 1 - 8

Rainfall (mm·year–1) 950 1700 2100 1900

Max temperature (˚C) 34.4 29.9 31.4 34.7

Min temperature (˚C) 10.4 8.7 13.8 7.6

Mean temperature (˚C) 22.2 18.2 20.3 19.7

Minimum RH (%) 37.9 45.0 50.8 41.8

Maximum RH (%) 84.3 95.2 85.4 98.5

Mean RH (%) 63.2 80.4 68.9 80.9

Wind speed (m·h–1) 0.93 0.64 0.43 0.35

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analyses were undertaken in soil laboratory of the Inter-

national Livestock Research Institute, Ethiopia, using the

standard laboratory procedures [10,11].

2.3. Data Anal yses

Analysis of variance in a nested design was performed

to compare the variations in soil properties among and

within the wild coffee forest areas. In this case, the soil

samples from sub-sites and profile depths were nested

under the four forests. Comparison between means was

carried out according to Tukey test at P = 0.05 whenever

the F-test declared significant differences. Moreover, the

relationships between soil variables were determined for

each area from Pearson correlations with the SAS sys-

tem for Windows-v8 (SAS Institute Inc. Cary NC, USA),

and graphs were prepared with SigmaPlot SPW9.0

(SYSTAT Software, Inc.).

3. RESULTS

Soils did not reveal significant variations for most

chemical properties, except for Mg, CEC and C:N.

However, the Berhane-Kontir soils had the highest pH

(6.23 ± 0.42), available K (1.71 ± 1.48 meq/100 g), ex-

changeable Ca (18.14 ± 8.07 meq/100 g), electrical con-

ductivity (0.12 ± 0.02) and available P (12.84 ppm) as

compared to others. On the other hand, the Yayu soils

had the lowest pH (5.39), available K (0.49 meq/100 g)

and TN (0.18%) contents. The average Ca content varied

from 9.00 to 18.14 meq/100 g in the Bonga and Berhane-

Kontir soils, respectively. Berhane-Kontir and Harenna

soils contained almost the same amount of exchangeable

Ca. The Berhane-Kontir soils had the significantly high-

est Mg (7.54 meq/100 g) as compared to the other soils,

which did not significantly differ between each other.

Significantly the lowest CEC (20.29 meq/100 g) was

determined for the Yayu soils in contrast to the highest

values (30.16 meq/100 g) in the Berhane-Kontir and

Harenna soils (29.15 meq/100 g). Similarly, the Ber-

hane-Kontir soils had higher electrical conductivity (EC)

values as compared to the other sites, with values rang-

ing between 0.09 and 0.12. Available P ranged from 0.35

to 12.84 ppm for the Bonga and Berhane-Kontir soils,

respectively, followed by Yayu (4.65 ppm) and Harenna

(0.90 ± 0.52 ppm). Conversely, the highest SOM was

found in the Harenna (4.9%) and Bonga (3.7%) soils, the

lowest at Berhane-Kontir (2.2%) and Yayu (2.6%).

Moreover, highly significant differences in C:N were

determined and the highest (12.41) and lowest (6.63)

values were obtained for the Harenna and Berhane-

Kontir soils, respectively (Table 2).

With regard to the influence of soil depth, the Harenna

soils showed significant differences in TN and SOM and

thus, C:N between the upper and lower layers. In the

upper layers, TN (0.34%) and SOM (6.42%) were higher,

while C:N (10.78) was lower than in the lower soil layer.

On the other hand, soil pH and EC were slightly increased

at the deeper profile. Accordingly, pH values ranged

between 6.04 and 6.35, which represent a slightly acidic

soil. Exchangeable bases, CEC and available P, however,

declined down the profile. The decline in available P was

significant at the Harenna and Yayu sites. On the other

hand, soils collected from the two depths at Bonga were

not statistically different for all the soil chemical pa-

rameters. However, soil sample from the surface layer

had relatively higher mean values for all the variables,

Table 2. Soil chemical properties (means ± SD) of the studied coffee forests.

Property Harenna Bonga Berhane-Kontir Yayu ANOVA

pH (H2O, 1:2.5) 6.19 ± 0.43 5.64 ± 0.72 6.23 ± 0.42 5.39 ± 0.41 Ns

K (meq/100 g) 0.51 ± 0.53 1.04 ± 0.07 1.71 ± 1.48 0.49 ± 0.31 Ns

Ca (meq/100 g) 18.10 ± 7.78 9.00 ± 0.95 18.14 ± 8.07 11.43 ± 1.44 Ns

Mg (meq/100 g) 3.21 ± 0.30b 3.35 ± 0.22b 7.54 ± 1.80a 3.21 ± 0.45b **

CEC (meq/100 g) 29.15 ± 5.85a 30.16 ± 4.81a 26.01 ± 1.53ab 20.29 ± 1.04b *

EC (1:2.5) 0.09 ± 0.05 0.09 ± 0.03 0.12 ± 0.02 0.09 ± 0.03 Ns

AP (ppm) 0.90 ± 0.52 0.35 ± 0.12 12.84 ± 8.35 4.65 ± 7.09 Ns

TN (%) 0.24 ± 0.03 0.25 ± 0.04 0.19 ± 0.07 0.18 ± 0.03 Ns

OC (%) 2.83 ± 0.83 2.14 ± 0.61 1.27 ± 0.48 1.51 ± 0.25 Ns

SOM (%) 4.87 ± 1.43 3.69 ± 1.05 2.18 ± 0.82 2.61 ± 0.44 Ns

C:N 12.41 ± 1.85a 8.55 ± 1.15b 6.63 ± 0.24b 8.54 ± 0.40b **

Ns = Not significant (P > 0.05), *P ≤ 0.05 and ** P ≤ 0.01. Means with the same letter within a row are not significantly different (Tukey test at P = 0.05).

T. Kufa / Agricultural Sciences 2 (2011) 443-450

446

except CEC, which increased from 28 to 32 meq/100 g.

Similar to Bonga, the Berhane-Kontir soils did not vary

due to profile depths and with the exception of pH and

EC, the values were slightly lower for deeper soils. At

Yayu, TN and SOM were significantly (P < 0.01) re-

duced from surface to sub-surface soils. C: N was also

significantly (P < 0.05) higher in the surface (9.24) than

in the deeper soil layer (7.83) (Ta b l e 3 ). Moreover, the

results of correlations between soil chemical properties

were found to be different among the four montane

rainforests (Table 4). Nonetheless, at all study sites, total

nitrogen (TN) of the soil was strongly correlated with

soil organic matter (P ≤ 0.001). In addition, there were

direct relationships between soil organic matter (SOM)

and inorganic ions (K, Ca, Mg) at all sites, and available

K and Ca in the Harenna soils correlated significantly.

The concentration of these soluble ions in the soil varied

slightly with soil reaction (pH).

4. DISCUSSION

The results do not differ in most of the soil chemical

properties, with the exception of significant differences

in CEC, Mg and C:N ratio. This could be related to the

similarity in forest vegetation and availability of suffi-

cient soil moisture during the different seasons. Accord-

ing to the general guidelines on the interpretation of soil

analysis results [11], the soils of the four study sites had

moderate TN. Soil organic carbon was ranked as moder-

ate for the Harenna and Bonga soils, but low in Yayu and

Berhane-Kontir. This could be attributed mainly to the

differences in the rate of decomposition and carbon se-

questration capacity of the soils. Similarly, the soils

contained exchangeable bases, ranging from medium to

very high. Nonetheless, the Ca content of the Bonga

soils was found to be low, while magnesium was very

high at all the study forests, possibly demonstrating the

similar soil-forming processes in the forest ecosystems

[12,13].

The relatively high total nitrogen contents at Harenna

and Bonga could be related to the release of mineralized

nitrogen upon decomposition unlike the relatively high

organic sources, which bind nitrogen in the organic form.

This shows the relatively higher mineralization rate at

the low altitude hot-humid Berhane-Kontir sites. This

was almost equal for the Bonga and Yayu forest soils.

The least C:N ratio at Berhane-Kontir suggests the in-

fluence of high temperature and higher microbial activity.

In general, the narrow C:N ratio indicates that the soils

contained low organic matter with ultimately increased

total nitrogen. This could minimize the competition for

the inorganic nitrogen between coffee trees and soil mi-

cro organisms, as opposed to the undecomposed materi-

als, and indicates decreased decomposition of organic

materials with an increased C:N ratio, which caused a

shortage of nitrogen in the soil similar to previous find-

ings [14]. The low C:N value could also be associated

with the contribution of leguminous shade trees to in-

crease nitrogen. The high rate of decomposition of or-

ganic material and the concentrations of acid-forming

ions, production of weak acids and basic cations could

also be amongst the possible reasons for this low C:N

ratio. Similar findings were reported elsewhere [15].

Table 3. Soil chemical properties (means ± SD) as influenced by profile depth at the four natural coffee forests of Ethiopia.

Exchangeable base (meq/100 g)

Site /depth

(cm)

(%)

SOM

(%)

(H2O, 1:2.5)

(1:2.5) K Ca Mg

CEC

(meq/100 g)

Available P

(ppm) C:N

Harenna * * Ns Ns Ns Ns Ns Ns *** *

0 - 20 0.34 ± 0.06a 6.42 ± 1.99a6.04 ± 0.42 0.07 ± 0.050.84 ± 0.8722.24 ± 9.583.29 ± 0.5833.53 ± 8.35 1.50 ± 1.14a 10.78 ± 1.58b

20 - 40 0.17 ± 0.03b 3.32 ± 0.92b6.35 ± 0.46 0.11 ± 0.060.18 ± 0.1913.97 ± 6.133.12 ± 0.0524.76 ± 3.32 0.30 ± 0.13b 14.05 ± 2.16a

Bonga Ns Ns Ns Ns Ns Ns Ns Ns Ns Ns

0 - 20 0.30 ± 0.07 4.53 ± 1.475.77 ± 0.81 0.10 ± 0.031.11 ± 0.2110.14 ± 2.503.47 ± 0.7328.10 ± 5.45 0.50 ± 0.28 8.73 ± 0.81

20 - 40 0.20 ± 0.02 2.85 ± 0.655.51 ± 0.64 0.08 ± 0.050.96 ± 0.347.85 ± 3.283.22 ± 0.5532.21 ± 6.92 0.20 ± 0.05 8.36 ± 1.49

B-Kontir Ns Ns Ns Ns Ns Ns Ns Ns Ns Ns

0 - 20 0.24 ± 0.10 2.88 ± 1.076.17 ± 0.56 0.12 ± 0.022.11 ± 2.0722.60 ± 9.918.14 ± 2.3424.09 ± 4.50 14.77 ± 7.38 7.05 ± 0.45

20 - 40 0.14 ± 0.05 1.48 ± 0.616.28 ± 0.40 0.12 ± 0.031.30 ± 0.9214.03 ± 9.066.94 ± 2.3127.93 ± 5.56 10.91 ± 9.37 6.20 ± 0.31

Yayu ** *** Ns Ns Ns * Ns Ns *** *

0 - 20 0.21 ± 0.02a 3.36 ± 0.47a5.54 ± 0.20 0.08 ± 0.020.70 ± 0.4513.04 ± 2.06a3.50 ± 0.3023.25 ± 2.28 8.90 ± 14.13a 9.24 ± 0.50a

20 - 40 0.14 ± 0.03b 1.85 ± 0.41b5.23 ± 0.62 0.09 ± 0.030.27 ± 0.179.82 ± 0.81b2.91 ± 0.6017.41 ± 1.97 0.40 ± 0.23b 7.83 ± 0.31b

Ns = Not significant (P > 0.05), *P ≤ 0.05, **P ≤ 0.01 and ***P ≤ 0.001. Means with the same letter within a column are not significantly different according to

Tukey grouping at P = 0.05. Abbreviations: TN = total nitrogen, SOM = organic matter, EC = electrical conductivity, CEC = cation exchange capacity, C:N =

carbon to nitrogen ratio.

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Table 4. Correlation matrix values between soil chemical properties at each coffee forest of Ethiopia.

Location Variable TN SOM pH EC K Ca Mg CEC AvP

SOM 0.93**

pH –0.22 0.002

EC –0.07 0.22 0.84*

K 0.78 0.93** 0.16 0.42

Ca 0.77 0.94** 0.31 0.52 0.95**

Mg 0.46 0.60 0.46 0.47 0.79 0.70

CEC 0.84* 0.97** 0.01 0.28 0.96** 0.95** 0.61

AvP 0.86* 0.93** –0.09 0.20 0.96** 0.86* 0.71 0.93**

Harenna

C:N –0.55 –0.22 0.54 0.60 0.00 0.08 0.05 –0.03 –0.24

SOM 0.97**

pH 0.71 0.84*

EC 0.11 0.15 0.04

K 0.22 0.18 –0.10 0.38

Ca 0.36 0.22 –0.20 –0.090.80

Mg 0.12 0.03 –0.25 –0.100.86* 0.90*

CEC –0.70 –0.66 –0.59 0.61 0.28 –0.15 0.03

AvP 0.81 0.76 0.45 –0.060.62 0.75 0.66 –0.56

Bonga

C:N 0.51 0.69 0.90* 0.23 –0.04 –0.34 –0.23 –0.32 0.32

SOM 0.99**

pH –0.31 –0.37

EC 0.22 0.14 0.78

K 0.80 0.72 0.20 0.66

Ca 0.86* 0.87* –0.67 –0.180.50

Mg 0.80 0.78 –0.62 –0.120.53 0.97**

CEC 0.02 –0.05 –0.51 –0.420.04 0.32 0.48

AvP –0.44 –0.36 –0.24 –0.77–0.71 –0.21 –0.28 0.04

B-Kontir

C:N 0.36 0.48 –0.21 –0.18–0.103 0.35 0.15 –0.64 0.29

SOM 0.99**

pH –0.04 0.02

EC 0.07 0.03 –0.93**

K 0.55 0.60 0.28 –0.43

Ca 0.57 0.60 0.53 –0.660.90*

Mg 0.71 0.68 –0.18 0.37 –0.02 0.11

CEC 0.80 0.76 0.12 –0.140.33 0.57 0.71

AvP 0.40 0.47 0.20 –0.310.94** 0.80 0.01 0.16

Yayu

C:N 0.97** 0.99** 0.07 –0.040.71 0.69 0.61 0.71 0.60

Correlations are significant at *P ≤ 0.05 and **P ≤ 0.01 (2-tailed).

There were also remarkable differences in the CEC of

the soils, the highest and lowest being from the Bonga

and Yayu soils, respectively. This is in line with the par-

ticle distribution of these soil types, i.e., higher sand

content in Yayu than in Bonga soils. Moreover, such

differences in CEC could also be attributed to differ-

ences in the humification and generation of pH-de-

pendent adsorptive sites on the organic exchange com-

plex. In this regard, several studies [12,13,16] pointed

out similar findings in coffee soils of Ethiopia. These

authors have associated soil fertility status with rainfall

and temperature gradients, and soil biochemical proc-

esses. Consequently, soils of high rainfall areas are

highly leached and weathered with low pH, poor satura-

tion of cation exchange complex, low total exchangeable

bases, low concentrations of available phosphorus and

total nitrogen. The present results for soil CEC and

available phosphorus were not consistent with the rain-

fall gradient, as the soil samples were taken under moist

forest covers at relatively shallow soil depths. The high

T. Kufa / Agricultural Sciences 2 (2011) 443-450

448

soil available phosphorus in the Berkane-Kontir soil as

compared to the others might come mainly from de-

composition of organic sources. Available P followed the

order of Bonga, Berhane-Kontir, Yayu and Harenna for-

est soils. The level of P at the Berhane-Kontir and other

forests is medium to low, respectively, according to the

standards [17]. This indicates the specific ability of each

soil type in fixing P. The highest SOM was found in the

Harenna and Bonga soils in contrast to the lowest SOM

at Berhane-Kontir and Yayu. At all sites, SOM was

higher than the range reported in forest soils [15]. The

relatively low available P in the Bonga soils could be

related to the capacity of the soil for fixing P due to the

high concentration of Aluminium (Al) and iron (Fe) in

the soil. As a result, several reports [4,13,18] also de-

scribed the limited availability of P in most coffee soils,

underlining the adaptation and low requirement of coffee

plants to P.

The higher TN and exchangeable bases in the upper

soils could partly illustrate the contribution of shading

and soil cover to reduce leaching and improve the nutri-

ent retention capacity of forest soils. The ratio of C:N

provides an indication of the type of organic matter pre-

sent in the soil and, in particular, the degree of humifica-

tion [2]. The C:N values of 12 and less than 10 indicate

good and impoverished (low organic matter content)

soils, respectively. However, the low C:N values ob-

tained at all forest sites except Harenna, demonstrate the

high concentration of TN in the soil, possibly from de-

composition of organic matter and/or nitrogen fixation.

This again could be associated to the climatic gradients

between the southeast and southwest montane rainforests.

Other authors [19,20] pointed out that the potential nu-

trient carrying capacity of the soil is determined by the

nature and the amounts of organic colloids present in the

soil.

The more humid the environment, the greater is the

proportion of recalcitrant organic matter. Moreover, clay

particles physically protect recent organic addition to

soils and form stable organo-mineral complexes with the

humus fraction [11]. In soils low in clay and receiving

small amount of annual precipitation, less soil organic

carbon is lost, because the capacity of the original soil

system to sequester carbon is reduced due to ready soil

aeration and the reduced physical protection of organic

matter by clay. The maximum available phosphorus at

Berhane-Kontir indicates its high fixation capacity. The

significant decline down the soil depth at Berhane-Kon-

tir and Yayu suggests that SOM and exchangeable bases

mitigate the fixation problem. The same findings on soil

P have been reported for the other coffee soils [4,18].

Despite the physical characteristics of the land and the

high rainfall patterns of the study sites, the inherent fer-

tility of the soil and thus quality of the land is main-

tained primarily due to the vegetation cover. The analy-

sis indicates that some soil attributes were noted to de-

cline with soil depth, suggesting the risks associated

with soil degradation. Therefore, assessment and man-

agement of SOM is important based on the recognition

that organic matter plays a role in the supply of major

and minor plant nutrients, improvement of physical and

chemical constraint, through reduced leaching, and fixa-

tion losses, as a storage for plant nutrients and a buffer-

ing against adverse conditions [13]. The bulk of coffee

soils in Ethiopia are classified as Nitosols, which are

highly weathered and originated from volcanic rocks

that require application of fertilizers for coffee cultiva-

tion under reduced shade environments. These soils are

deep and well drained and have medium to high contents

of most of the essential elements, except nitrogen and

phosphors [4,13]. Altogether, soils of the study areas can

be classified as Humic Nitosols, which occurs in areas

with high precipitation, mainly under natural vegetation

in the lowlands and in the highlands [21].

Forests play a pivotal role in maintaining ideal soil

properties and hence fauna and flora of the forest eco-

system. To this end, our present results provide high-

lights the roles of less forest disturbances in maintaining

high quality soils and coffee diversity in the natural cof-

fee forests of southeastern and southwestern Ethiopia. In

the semi-forest coffee production system, the level of

human interventions is minimal merely to systematically

remove the dense shading and undergrowth weeds,

largely to facilitate coffee harvesting [22]. The wild cof-

fee forest soils were characterized by ideal chemical

fertility status with high soil organic matter and major

plant nutrients. This may be attributed to the high litter

fall mainly from indigenous upper canopy shade trees.

The results corroborate with other authors [9,23,24] who

reported the adverse impacts of deforestation on coffee

ecology and natural gene pools. The declining soil fertil-

ity across locations and profile demonstrated the need

for site-specific forest management for enhanced organic

coffee production and benefit from the premium interna-

tional coffee prices [25]. Hence, exerting efforts to con-

serve the fragmented forest areas is thus parts and parcel

of making sound land use planning with full local com-

munity participations and fair benefit sharing to improve

the livelihoods of the rural poor. This demands strong

international collaborations and participation of the local

communities [26].

5. CONCLUSIONS AND MANAGEMENT

IMPLICATIONS

The study show inter- and intra-forest variations in

soil characteristics of the montane rainforests, possibly

T. Kufa / Agricultural Sciences 2 (2011) 443-450

449449

due to the effects of forest management, vegetation

composition, site variables, parent materials and climate

gradients presented in Table 1. Moreover, significant

variations were detected between soil profile depths for

most soil properties could demonstrate the possible ad-

verse impacts of human induced soil erosion from culti-

vated lands. The present findings underline the contribu-

tions of vegetation cover in building up high quality soil

fertility status and preventing run-off on steep slopes.

Hence, the opened up plots should deserve special atten-

tion of rehabilitation works of future management inter-

ventions.

The declining soil fertility across locations and profile

demonstrated the need for site-specific forest manage-

ment. However, studies on seasonal variations in dy-

namics of carbon sequestration, nitrogen sources and

mineralization processes call for further works. To ex-

haust the present findings and use soil properties as geo-

graphical indicators, more transects within and around

each study remain to be assessed over seasons and

across locations. To ensure traceable specialty coffees,

there is a need for comprehensive works on the relation-

ships between quality attributes and environmental as

well as soil factors. This study would also provide prac-

tical implications for cost-effective environmental sus-

tainability and utilization of the remnant forest land-

scapes, maximum biodiversity and functioning ecosys-

tem services for global benefits. As to what extent forest

management levels, composition of plant species, parent

materials, soil microorganism and biochemical process

can dictate soil fertility status are among the focussed

areas that deserve attentions. The friendly coffee forest

environments are highly vulnerable to climate change

patterns and thus also require especial mitigation and

adaptation strategies. Moreover, in view of the ever in-

creasing population pressure, the trade-offs between

agricultural productivity, quality, biodiversity, and eco-

system goods and services call for strong collaborations

between the national and international actors to ensure

sustainability components (environmental, economical

and social) for the well being of the global population in

general and Ethiopian people in particular.

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