Applied and Environmental Soil Science
Volume 2020 (2020), Article ID 3713967, 9 pages
https://doi.org/10.1155/2020/3713967

Research Article

Fertility Status of Acid Soils under Different Land Use Types in Wolaita Zone, Southern Ethiopia

Mesfin Kassa Cholbe,¹ Fassil Kebede Yeme,² and Wassie Haile Woldeyohannes³

¹Department of Plant Science, College of Agricultural, Wolaita Sodo University, P.O. Box 138, Sodo, Ethiopia
²Mohammed VI Polytechnic University, Lot 660, Haymoulary Rachid, Banguerir 43150, Morocco
³School of Plant and Horticultural Science, Hawassa University, P. O. Box 05, Hawassa, Ethiopia

Correspondence should be addressed to Mesfin Kassa Cholbe; mesfine2004@gmail.com

Received 1 February 2020; Revised 7 March 2020; Accepted 19 March 2020; Published 19 October 2020

Academic Editor: Claudio Cocozza

Copyright © 2020 Mesfin Kassa Cholbe et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Information on soil fertility status of acid soil of a particular area as affected by land use type is important for developing sound soil management systems for improved and sustainable agricultural productivity. The main objective of this study was to assess the fertility status and effect of land use change on soil physicochemical properties. In this study, adjacent three land use types, namely, enset-coffee, crop, and grazing land use were considered in four districts (i.e., Bolos Sore, Damot Gale, Damot Sore, and Sodo Zuria) of Wolaita Zone, southern Ethiopia. Soil samples were collected from a depth of 0–20 cm from each land use type of the respective districts for physicochemical analyses. The results showed that land use types significantly affected () soil properties such as bulk density, available P, exchangeable potassium, exchangeable acidity, exchangeable bases (Na, K, Ca, Mg), exchangeable acidity, and CEC. Besides, soil pH, OC, and TN were influenced significantly () both by districts and land use types. The very strongly acidic soils were found predominantly in the crop and grazing lands whereas a neutral acidity level was found in the enset-coffee land use type of four districts. In conclusion, the study proves that land use type change within the same geographic setting can affect the severity of soil acidity due to over cultivation and rapid organic matter decomposition. Finally, the study recommends an in-depth study and analysis on the root causes in aggravating soil acidity under crop and grazing land use types.

1. Introduction

Agricultural sustainability requires periodic evaluation of soil fertility status, which is important in understanding factors that impose serious constraints to crop production under different land use types and for adoption of suitable land management practices [1]. The land-use systems play a tremendous role in influencing nutrient availability and cycling and may also influence secondary succession and biomass production [2, 3]. Soil acidity and associated low nutrient availability are key constraints to crop production in acidic soils, mainly Nitisols of Ethiopian highlands [4]. Haile et al. [5] estimated that ∼43% of the Ethiopian crop land is affected by soil acidity). The soil acidity in Ethiopia is dominated by strong acid soils (pH 4.1–5.5) [6]. The decline in soil fertility is caused by land use type changes [7]. The loss of soil fertility in Ethiopia is related mainly to cultural practices such as low fertilizer use, removal of vegetative cover, and burning plant residues or the annual burning of vegetation on grazing land. In addition to soils developed from parent materials low in carbonate minerals, soil acidification takes place in areas where mean rainfall exceeds evapotranspiration [5]. The existence of high exchangeable acidity in a soil usually demonstrates the occurrence of exchangeable hydrogen, exchangeable aluminum as either Al³⁺ or partially neutralized Al-OH compounds such as Al (OH) ³⁺, and weak organic acid ions held at the colloidal surfaces of the soil [8]. The specific adsorption of organic anions on hydrous iron and Al surfaces and the corresponding release of hydroxyl ions could also increase the pH and available P in the soil solution. Similar to the western, southern, and central highlands of Ethiopia, severe soil acidity problem has been reported recently in the highland areas of Wolaita Zone, southern Ethiopia. However, the degree, extent, and causes of the problem had not been yet examined. The major agricultural constraints in Wolaita area are shortage of land for crop cultivation and livestock grazing, decline of soil fertility, rainfall variability, and pests and diseases. Nowadays, due to increasing population pressure and shortage of land, deforestation and cultivation activities are being carried out on steep slopes, which accelerate soil erosion. Indeed, there are limited efforts in the study area to tackle soil acidity through the use of lime although the scale of operation is not commensurate with the problem. Knowledge on the distribution, degree, extent, and causes of severe soil acidity in the Wolaita can assist policy makers, researchers, extension workers, and farmers to improve the fertility and productivity of the acid. Thus, this study was conducted to determine the physicochemical properties of different land use types and extents of soil acidity of the Wolaita Zone, southern Ethiopia.

2. Materials and Methods

2.1. Description of the Study Sites

The study was conducted in Sodo Zuria, Damot Gale, Damot Sore, and Boloso Sore districts of Wolaita Zone, southern Ethiopia (Figure 1) during 2015. This zone is located at 385 km to south west from Addis Ababa, capital city of the country. These districts were purposely selected because they have high population, land shortage, over grazing, and high agriculture potential from the 12 districts in Wolaita Zone. The sites are located between 037°35′30″–037°58′36″E and 06°57′20″–07°04′31″N with altitudinal range of 500 to 2950 m above sea level. As per the recent nine years (2007–2015) climatic data, the mean annual rainfall is about 1355 mm (Figure 2). The mean average monthly temperature for the last nine years is 20°C [9].

Figure 1: Location of the study sites, Wolaita districts, southern Ethiopia.

Figure 2: Nine years (2007–2015) mean monthly rainfall and mean maximum and minimum temperatures of the study areas [9].

2.2. Soil Sampling Design and Procedure

A randomized complete block research design used for collecting soil samples in the three representative land use types and four districts (Sodo Zuria, Damot Gale, Damot Sore, and Boloso Sore) with three replications of each at three peasant association, which are similar in their agro ecology, altitude, and slope, were selected. After the selection of the three peasant association, the land use types were systematically selected on the basis of contour line, similarity in soil color by visual observation, slope and altitude to reduce their natural difference, and soil type diversity impacts on the soil acidity. A total of 108 soil samples were collected in triplicates from the three land use types of both sites. Each composite soil sample was prepared from 15 subsamples taken by inserting an auger to a depth of 20 cm from randomly marked sampling points of each land use types at both sites.

2.3. Soil Sampling and Preparation

Soil samples were air-dried, ground, and passed through 2 mm sieve at the Soil Laboratory of the Hawassa Research Center. The physicochemical analyses of the soil samples were conducted at Regional Soil Laboratory following standard laboratory procedures. The bulk density determinations were done at Soil Laboratory in Wolaita Sodo University, College of Agriculture. Triplicate soil samples from each sites and land use types were collected.

2.4. Soil Laboratory Analysis

The collected composite soil samples were air-dried, ground, and sieved to pass through a 2 mm sieve except for soil organic carbon (OC) and total N (TN) analysis which were passed through 0.5 mm sieve. Soil particle size distribution was determined by hydrometer using Bouycous method [10]. Soil pH in water was determined with a digital pH meter at soil: water ratio of 1 : 2.5 [11]. The reserve acidity was measured in 0.1 M CaCl₂ using the same pH meter at the soil: 0.1 M CaCl₂ ratio of 1 : 2.5 [12]. The ΔpH was calculated by subtracting soil pH (KCl) from soil pH (H₂O). Bulk density was determined using the core sampling method [13]. Total porosity of the soil was calculated from the soil bulk and the particle densities; where 2.65 g·cm³ was used as a standard value for soil particle density; soil moisture content was measured by gravimetric method [11]. Organic carbon content of the soils was determined following the wet combustion method of Walkley and Black as outlined by Sahlemedhin and Taye [14]. Soil total nitrogen was analyzed by wet-oxidation procedure of the Kjeldahl method [15]. Available phosphorus was measured by following Bray II extraction using spectrophotometer [16]. Exchangeable Ca and Mg were measured from the extract with atomic absorption spectrophotometer (AAS), while exchangeable K and Na were determined by flame photometer. Exchangeable acidity was analyzed by [17]. Aluminum saturation percentage was calculated as the ratio of the exchangeable Al to CEC of the respective soil samples random powder method, and calcium carbonate content was determined by rapid titration method as described by Black [18]. Available Fe, Mn, Zn, and Cu were extracted by diethylene triamine pentaacitic acid (DTPA) method by using AAS [19].

2.5. Statistical Analysis

Mean comparisons using the least significant difference (LSD) test at probability of 5% level were done for the different land uses systems and correlation analysis has been done for the different soil properties and land uses systems using the SAS software [20], to see the relationship between parameters.

3. Results and Discussion

3.1. Effect of Land Use Types and Locations on Physical Fertility of Acid Soils

The textural analysis results revealed that 75% of all the land use types considered in this study were found to be clay loam (Table 1). However, sand, silt, and clay content in these soils were varied significantly () among the land use types. According to Hazelton and Murphy [21], who rated all sand, silt, and clay contents of soils into high (>40%), moderate (25–40%), and low (10–25%), the sand contents high in soils of enset-coffee land use of all locations and crop and grazing land uses were moderate (Table 1). The silt to clay ratio was 0.7, which is significantly lower than enset-coffee and crop land uses of Damot Gale district. Averaged over locations, values for Damot Sore crop land (0.8), grazing land (0.8), Sodo Zuria grazing land (0.9), Damot Gale grazing land (0.7), and Boloso Sore (0.8) grazing land uses showed similar trends due to the fact that the soils were might be of similar origin. It has been reported that silt/clay ratios less than unity indicate low values, signifying that the soils are pedogenically ferraltic in nature [22].

Table 1: Mean values (n = 108) of particle size distribution and texture class of different locations and land use types of study areas.

Sodo zuria
Damot gale

Land use types
Particle size distribution
Silt/clay ratio
Texture class
Particle size distribution
Silt/clay ratio
Texture class

Sand %
Clay %
Silt %
Sand %
Clay %
Silt %

Enest-coffee
35a
33a
29a
1.0
Clay loam
22a
37a
25a
0.8
Sandy clay loam

Crop land
39b
29b
33b
1.1
Clay loam
40b
26b
50b
2.0
Clay loam

Grazing land
26c
38c
38c
0.9
Clay loam
38c
37a
25a
0.7
Clay loam

Mean
40
30
33
0.9

40
30
30
1.0

CV (%)
12
12
11

10
13
10

LSD (0.05)
7
8
8

10
13
9

Damot sore
Boloso sore

Enest-coffee
28a
24a
35
2.4
Silt loam
28a
39a
25a
1.3
Clay loam

Crop land
41b
39b
33
0.8
Clay loam
36b
26b
46b
1.8
Loam

Grazing land
31c
37c
32
0.8
Clay loam
36b
35c
29c
0.8
Clay loam

Mean
29
35
43
1.1

32
29
35
1.1

CV (%)
10
13
10.1

8.6
7.8
9.4

LSD (0.05)
5
3
7

4
5
7

CV = coefficient of variation, LSD = least significant difference.

3.2. Soil Bulk Density and Total Porosity of Acid Soils

Bulk density value was not significantly () affected by land uses and locations (Table 2). However, numerically the highest mean (1.39 g·cm⁻³) value of bulk density was recorded on the Boloso Sore crop land and the lowest mean (0.98 g·cm⁻³) value under Damot Gale enset-coffee land (Table 2), which might be resulted from compaction of soil due to intensive cultivation in all locations of the crop land. Soil bulk density was positively and significantly correlated with the silt and negatively (r = −0.95) with total porosity of the soil, respectively. This might be due to the reciprocal relationship between soil bulk density and total porosity, which shows the degree of soil compaction. Similar results were reported by Takele et al. [1]; Abad et al. [23] suggested that the bulk density of cultivated land was higher than that of adjacent grazing land.

Table 2: Mean valves of (n = 108) some selected physical properties of different locations and land use types of study areas.

Sodo zuria
Damot gale

Land use types
BD (g·cm⁻³)
TP (%)
MC (%)
WHC (%)
BD (g·cm⁻³)
TP (%)
MC (%)
WHC (%)

Enest-coffee
1.12a
59.02a
19.90a
24.95a
0.98a
64.36a
18.53a
22.78a

Crop land
1.33b
51.51b
18.14b
21.43b
1.16b
57.57b
18.05b
22.06a

Grazing land
1.28c
53.12c
19.95c
24.95c
1.20c
56.24c
20.59c
26.34b

Mean
1.24
54.55
19.33
23.78
1.11
59.39
19.09
23.72

CV (%)
12.05
10.03
7.83
10.47
8.58
5.86
8.63
10.07

LSD (0.05)
0.15
5.47
1.51
2.49
0.09
3.46
1.64
2.38

Damot sore
Boloso sore

Enest-coffee
1.08a
59.38a
20.05a
26.15a
1.24a
54.73a
20.85a
26.37a

Crop land
1.18b
54.05b
19.70b
24.55b
1.39b
49.41b
18.52b
22.78b

Grazing land
1.14c
58.54c
20.71a
25.08b
1.35c
51.38c
18.44b
22.76b

Mean
1.13
57.32
20.71
25.26
1.33
51.84
19.27
23.97

CV (%)
4.89
2.47
2.31
2.86
8.85
7.75
6.64
7.86

LSD (0.05)
0.05
1.41
0.46
0.72
0.11
4.01
1.27
1.88

BD = bulk density, TP = total porosity, MC = moisture content, and WHC = water holding capacity.

3.3. Soil Moisture Content and Water Holding Capacity

Moisture content and WHC of the soils were significantly () affected by land uses (Table 2). Considering the effects of land use, the highest (20.71%) in Damot Gale enset-coffee land and lowest (18.05%) crop land. Similarly, the highest moisture content was record (26.37%) and lowest was record from (21.43%) water holding capacity were recorded in the enset coffee and crop land, respectively. Similar results were reported by Mengistu et al. [24] that the water content at PWP was highest (19.71%) under the forest land and lowest in the grazing land (16.17%) and the cultivated land 16.56%.

3.4. Effect of Land Use Types and Locations on Chemical Fertility of Acid Soils

3.4.1. Active and Exchangeable Acidity

The pH (H₂O, KCl and CaCl₂) values of the soils varied between 5.12 to 7.0, 4.21 to 6.31, and 4.3 to 6.50 in different locations with land use types, respectively. Based on the rating suggested by Hazelton and Murphy [21], the soils can be categorized as strongly acidic to neutral, very strongly acidic to slightly acidic, and extremely acidic to slightly acidic pH (H₂O, KCl and CaCl₂), respectively. It was lowest in soils of the Sodo Zuria grazing land use, and the highest soil pH value was also recorded in the Damot Gale enset-coffe land use compared to the crop and grazing land soils. Similarly, the lesser average soil pH in the crop and grazing lands is apparently due to the excessive removal of organic cations and associated cations by crop produce and over grazing, respectively, that they would not have a chance to return back and neutralizes the acid soil. In line with this, Mengistu et al. [24] pointed out that although acidity is naturally occurring, removal of plant residues carrying organic anions and excess cations from the farm or paddock is likely to accelerate soil acidification. The change in pH between [pH (H₂O) and pH (KCl, CaCl₂)] was greater than or equal to one across the soils sampling sites (Table 3). Soil pH (KCl) indicated the potential acidity and presence of weatherable minerals when the difference between pH (H₂O) and pH (KCl) is greater than unity [25]. Reserve acidity indication of the soil samples pH was found to range from 4.3 to 6.50 in different locations with land use types. The reserve acidity of soil was always higher than the active acidity. The difference between reserve and active acidity, ΔpH, of the studied soils was positive and found to range from 0.23 to 1.80 in different locations. This indicated that the studied of Damot Sore and Boloso Sore soil samples had considerable more reserve acidity in the soils. Tsehaye et al. [26] reported ΔpH values, which are to be in the range of 0.8 to 1.3 with a mean of 1.0. The reserve acidity values of the soils revealed that the reserve acidity value changes with different sites as well as with the land use types as observed for the case of active acidity.

Table 3: Mean values of soil pH (n = 108) and change of soil pH across different locations and land use types of study areas.

Sodo zuria
Damot gale

Land use types
pH H₂O
pH KCl
pH CaCl₂
ΔpH KCl
ΔpH CaCl₂
pH H₂O
pH KCl
pH CaCl₂
ΔpH KCl
ΔpH CaCl₂

Enest-coffee
6.34a
5.85a
6.11a
0.49
0.23
7.01a
6.31a
6.50a
1.09
0.90

Crop land
5.30b
4.41b
4.71b
0.90
0.59
6.20b
4.80b
5.32b
1.40
0.90

Grazing
5.12c
4.37c
4.63c
0.75
0.75
6.10b
4.81b
5.10c
1.29
1.00

Mean
5.60
4.81
5.10
0.71
0.52
6.43
5.30
5.60
1.20
0.90

CV (%)
9.51
6.89
6.33
—
—
5.74
7.10
5.69
—
—

LSD (0.05)
0.53
0.33
0.32
—
—
0.38
0.37
0.32
—
—

Damot sore
Boloso sore

Enest-coffee
6.70a
6.61a
5.72a
0.09
0.98
6.60a
5.30a
5.60a
1.30
1.00

Crop land
6.00b
5.80b
4.60b
0.20
1.40
6.00b
4.30b
4.70b
1.70
1.30

Grazing land
6.10b
5.72c
4.30c
0.38
1.80
5.60c
4.21b
4.61b
1.40
1.00

Mean
6.26
6.04
4.87
0.22
1.39
6.00
4.60
4.90
1.40
1.10

CV (%)
9.40
10.5
11.30
—
—
7.61
12.60
11.10
—
—

LSD (0.05)
0.59
0.64
0.75
—
—
0.46
0.68
0.56

3.5. Exchangeable Base

Average exchangeable Ca, Mg, K, and Na ions are presented in Table 4 which showed significant () variation among difference locations within land use types. The exchangeable bases were low in both the soils of the crop and grazing land use types as compared to that of the enset-coffee land use. Hence, the low CEC and exchangeable cations in the crop land and grazing lands are clearly attributed to the presence of relatively low pH. The low-pH soil colloids are sites that adsorb hydroxy-aluminum and cease to function for cation exchange thereby could reduce the CEC of a soil. Exchangeable Ca was dominant in the exchange sites of the soil colloidal materials of the soil studied; this was followed by Mg, K, and Na ions in that order. However, Bore and Bedadi [27] reported that the highest and lowest exchangeable Ca were in the forest (25.4 Cmolc kg⁻¹) and grazing 15.2 Cmolc kg⁻¹) lands, respectively.

Table 4: Mean values (n = 108) of exchangeable base and percentage of base saturation in different location and land use types of study areas.

Sodo zuria
Damot gale

Land use types
Ex.Ca
Ex.Mg
Ex.K
Ex.Na
PBS
Ex.Ca
Ex.Mg
Ex.K
Ex.Na
PBS

(C molc·kg⁻¹)
(%)
(C molc·kg⁻¹)
(%)

Enest-coffee
9.10a
4.50b
1.20a
0.34a
74.47a
11.44a
3.53a
0.75a
0.18a
85.02a

Crop lantd
8.76b
4.39a
0.24b
0.23b
70.80b
11.26b
3.22b
0.31b
0.14b
78.45b

Grazing
8.46c
4.10c
0.57c
0.34a
70.48a
11.08c
3.46c
0.68c
0.17a
80.25b

Mean
8.77
4.33
0.67
0.30
71.91
11.26
3.40
0.56
0.16
81.24

CV (%)
4.30
5.66
9.60
5.72
10.52
8.82
10.20
8.60
8.50
11.98

LSD (0.05)
0.47
0.35
0.20
0.15
0.56′
0.16
0.75
0.18
0.05
0.86

Damot sore
Boloso sore

Enest-coffee
11.40a
3.40a
0.37a
0.17a
72.35a
10.15a
3.85a
0.44a
0.33a
83.92a

Crop land
11.13b
3.13b
0.21b
0.16b
71.01a
10.43b
3.37b
0.26b
0.26b
81.36b

Grazing
9.93c
3.30c
0.29c
0.17a
70.20b
10.40b
3.84a
0.31a
0.31a
79.89c

Mean
7,95
3.27
0.29
0.16
71.21
10.32
3.68
0.33
0.30
81.72

CV (%)
4.94
5.36
8.80
7.40
10.67
4.33
8.03
6.36
7.60
12.34

LSD (0.05)
0.47
0.21
0.23
0.21
0.67
0.46
0.44
0.02
0.12
0.41

As per the ratings of FAO [28], the exchangeable Na in the soils of the sampling sites was low; the exchangeable Ca and Mg were medium to high in all sites which had high values while the exchangeable K was low except the enset-coffee land use in Sodo Zuria and Damot Gale sites which had high values, while the exchangeable K was low except the enset-coffee land use in Sodo Zuria and Damot Gale sites which had high values in contradiction with the generally held view that Ethiopia soils are rich in potassium [29]. The present studies are in line with Teshome et al. [30] who observed highest and lowest exchangeable Ca in forest and cultivated lands, respectively, in western Ethiopia of Ababo area.

Potassium to magnesium ratio of the studied soils varied from 0.05 : 1 to 0.26 : 1, which indicated Mg-induced K deficiency using the rating of Laekemariam [31]. This can be corrected by K application to bring the K to Mg ratio closer to one. If there is a high preferential K adsorption on the exchange sites of clay minerals, the amount of K desorbing may then decline, resulting in a reduced K uptake at low soil exchangeable K to Mg ratio. Therefore, attempts should be made to supply the plants with potassium in physiologically correct ratio and in a sustainable manner. Loide [32] suggested indicative K: Mg ratios of 0.7 : 1 and 1 : 1 for clay and loamy textured soils, respectively. In silt loam textured soils of Damot Gale, the K: Mg ratio varied from 0.2 to 1.6, while the ratio ranged between 0.1–1.5 in clay textured soils of Damot Sore and Sodo Zuria districts. Accordingly, to these, silt loam soils and clay soils had shown Mg induced K deficiency. Similar trends were obtained on K: Ca ratio in different land uses and sites.

Table 5: Mean values (n = 108) of basic cation saturation ratio, K saturation percentage, and calcium carbonate in different locations and land use types.

Sodo zuria
Damot gale

Land use types
K : Mg
K : Ca
Ca : Mg
K-index %
CaCo₃ %
K : Mg
K : Ca
Ca : Mg
K-index %
CaCo₃ %

Enest-coffee
0.26a
0.13a
2.02a
0.06a
24.15a
0.21a
0.06a
3.24a
0.04a
23.70a

Crop land
0.05c
0.03b
1.99b
0.01b
23.92b
0.09c
0.03b
3.44b
0.02b
23.20b

Grazing
0.14b
0.07b
2.06a
0.03b
23.56b
0.19b
0.06a
3.25a
0.03b
22.70c

Mean
0.15
0,07
2.02
0.03
23.87
0.16
0.05
3.31
0.03
23.20

CV (%)
7.70
7.90
11.11
6.53
10.73
6.55
6.89
12.23
5.47
12.70

LSD (0.05)
0.02
0.04
0.13
0.04
1.56
0.21
0.02
0.14
0.01
1.95

Damot sore
Boloso sore

Enest-coffee
0.11a
0.03a
3.35a
0.02a
23.02a
0.11a
0.04a
2.63a
0.02a
23.17a

Crop land
0.07b
0.02b
3.5b
0.01b
22.64b
0.08b
0.02b
3.10b
0.01b
23.05b

Grazing
0.08b
0.03b
3.01b
0.01b
22.12b
0.08b
0.03b
2.70c
0.01a
21.10b

Mean
0.08
0.02
3.30
0.01
2259.
0.09
0.03
2.81
0.01
22.44

CV (%)
10.11
9.82
12.10
5.10
6.44
9.10
6.71
10.10
4.50
8.33

LSD (0.05)
0.01
0.06
0.25
0.01
1.38
0.10
0.02
0.32
0.01
1.87

The calcium to magnesium ratio across studied districts using the rating of Laekemariam [31] has shown the low level of Ca (1–4) on 35% and balanced (4–6) on 60% and low Mg (6–10) on 5% of the samples. These rates are lowest in Sodo Zuria crop land (1.99) and highest in Damot Sore crop land (3.55). This shows that soils under the land uses are of low fertility probably due to intense land use practice and excessive loss of Ca through leaching by the high tropical rainfall [33]. Addition of lime and organic manure can be used to supply Ca and improve soil fertility under the land use types [34].The observed order of cation in the exchange complex (Ca > Mg > K > Na) could also support the existence of Mg induced K deficiency (Table 5). Hence, K-containing fertilizer should be considered for soils of the study areas. It has been suggested that the proportions of the basic cations of the effective CEC are more relevant to plant performance than the actual levels [21]. According to Havlin et al. [35]; the range of critical values for optimum crop production for K, Ca, and Mg are from 0.28–0.51, 1.25–2.5, and 0.25–0.5 C mol·kg⁻¹ soil, respectively. Accordingly, the exchangeable K, Ca, and Mg contents of the soils are above the critical values. However, this does not prove a balanced proportion of the exchangeable bases. Potassium uptake would be reduced as Ca and Mg are increased; conversely, uptake of these two cations would be reduced as the available supply of K is increased [35]. In addition, the ratio of exchangeable Ca: Mg should not exceed 10 : 1 to 15 : 1 to prevent Mg deficiency and also the recommended K: Mg is < 5/1 for field crops, < 3/1 for vegetables and sugar beets, and <2/1 for fruit and green house crops [35].

There was great variation in effective cation exchange capacity (ECEC) of the soils under the different land use systems (Table 6). The highest and lowest ECEC were recorded at Damot Gale enest coffee land and Sodo Zuria grass land, whilst the values (14.10 C molc·kg⁻¹ and 15.02 C molc·kg⁻¹) were recorded in the crop land at Sodo Zuria and Boloso Sore respectively. In line with ECEC, the highest value of CEC (21.20 Cmolckg⁻¹ was observed in Damot Sore enset-coffee land soil and the lowest (17.60) was recorded in Bolos Sore crop land, the CEC value was not consistent showing that there was no significance difference among different land use systems (Table 6). According to Mesfin et al. [36] in Wolaita soils showed that kaolinite is 29.8% for Damot Sore and 7.8% for Damot Pulasa Districts.

Table 6: Mean values (n = 108) of cation exchangeable capacity in different locations and land use types.

Sodo zuria
Damot gale

Land use types
ECEC
CEC soil
CECap
ECEC
CEC soil
CECap

(C molc·kg⁻¹)
(C molc·kg⁻¹)

Enest-coffee
15.56
20.33a
70.10
16.36
18.70a
93.50

Crop land
14.10
19.22b
66.27
15.36
18.80a
72.30

Grazing land
13.92
19.11b
50.28
16.07
19.40b
52.43

Mean
14.52
19.55
62.21
15.93
18.96
72.74

CV (%)

11.10

12.01

LSD (0.05)

1.56

2.09

Damot sore
Boloso sore

Enest-coffee
15.72
21.20a
93.36
15.42
17.60a
67.69

Crop land
15.17
20.60b
52.82
15.02
17.60a
55.00

Grazing land
15.58
19.50b
52.70
15.35
18.60b
53.14

Mean
15.67
20.43
66.29
15.26
17.93
58.61

CV (%)

11.6

10.3

LSD (0.05)

1.79

1.85

3.6. Organic Carbon, Total Nitrogen, Available Phosphorus, and Carbon to Nitrogen (C: N) Ratio

The data in Table 7 showed the OC, TN, and available P contents of the soils studied. According, to the rating suggested by Karltun et al. [37]; the soil OC content was low in range (1.30 to 1.71%). Moreover, the TN contents of all the soils studied were in the low ranges (0.13 to 0.19%). Hazelton and Murphy [21] classified soil organic carbon percentages of <1.0, 1.0–1.71, 1.72–3.0, 3.1–4.29, and >4.3 as very low, low, medium, high, and very high, respectively. The lowest amount of organic matter in the soil might be due to low addition of crop residue, and continuous cultivation and rapid oxidation of soil OM. In conformity to the present observation, complete removal of aboveground biomass [30, 38], intensive cultivation [39], insufficient application of organic inputs [38] and and Wolaita agricultural land [31].

Table 7: Mean Values (n = 108) of organic carbon (OC), total nitrogen (TN), and available Phosphorus (Av.P) in different locations and land uses.

Sodo zuria
Damot gale

Land use types
TN
Av.P
OC
C : N
TN
Av.P
OC
C : N

(%)
(mg kg⁻¹)
(%)
(mg kg⁻¹)
(%)

Enest-coffee
0.17a
18.70a
1.60a
9.41
0.14a
20.58a
1.70a
12.14

Crop land
0.16b
10.57b
1.50b
9.37
0.12b
11.74b
1.60b
13.33

Grazing
0.16b
12.00c
1.60c
10.00
0.12b
14.56c
1.70a
14.16

Mean
0.16
13.76
1.56

0.30
15.63
1.66
13.21

CV (%)
6.10
10.65
11.7

12.1
11.39
11.1

LSD (0.05)
0.05
1.46
0.10

0.01
2.24
0.10

Damot sore
Boloso sore

Enest-coffee
0.17a
17.72a
1.71a
10.05
0.19a
16.87a
1.41a
7.42

Crop land
0.13b
10.70b
1.40b
10.76
0.15b
7.44b
1.30b
8.66

Grazing
0.19c
13.87c
1.40b
7.36
0.16b
8.25b
1.51c
9.43

Mean
0.16
14.10
1.50
9.39
0.16
10.85
1.40

CV (%)
5.70
11.88
8.55

8.63
11.59
8.62

LSD (0.05)
0.05
2.23
0.14

0.04
2.34
0.14

The carbon to nitrogen (C: N) ratio of the soils also varied between 7.36 and 14.16. The carbon to nitrogen (C: N) ratios of the soils at Wolaita zone was significantly affected by soil land use types () (Table 7). On the other hand, although slight numerical variation was observed among the location, C/N ratio was not significantly affected by locations. This indicates that the rate at which total N decreased with land use types was much higher than reduction in carbon. Therefore OM and TN content have direct relation to soil acidity. The present finding was in line with Yihenew and Getachew [40] who reported highest values of C: N contents under grazing land use in northwestern Ethiopian soils. Mesfin et al. [36] revealed that available P with both Olsen and Bray II extraction methods for Wolaita acidic soils were low. The lowest available P (7.44) was observed in strongly acidic soil (crop land of Boloso Sore District). This may be due to the P fixation with Fe and Al as indicated by the favorable acidic soil reactions indicated by the results of the present study.

3.7. Available Micronutrients

The contents of available micronutrients (Fe, Mn, Zn and Cu) were significantly () affected by land use, location and their interaction of land use and location (Table 8).The range value of micronutrients for the entire districts in their order is indicated as follows Fe (97.30 to 182), Mn (116.50 to 147.30), Zn (8.98 to 12.77) and Cu (0.23 to 6.33 mg·kg⁻¹) and considering the ratings proposed by FAO [28] across district had sufficient (Fe, Mn, Zn) and Cu low to optimal contents. The highest contents of Fe, Mn, Zn and Cu were recorded under the enset-coffee and grazing land uses of four sites (Table 8), while the lowest contents of Fe, Mn, Zn and Cu were observed under the crop lands of four sites. Likewise, EthioSIS [6] reported sufficient Mn levels in different soil types of Ethiopia including Vertisols. Znic deficiency is mostly not expected on acidic soil [41]. The results reported that Mehlich 3 extracts comparable amounts of micronutrients (Fe, Zn, and Mn) were the sufficiency for Wolaita soil [31].Generally, Cu content in all soil samples of study districts were found to be yield limiting nutrients, whereas Fe, Mn and Zn levels were sufficient for crop production. It was accounted to low level of soil OM. In line with this finding, the study in some Nitisols of Ethiopia indicated Cu deficiency [39].

Table 8: Mean values of (n = 108) available micronutrients in different location with land use types.

Sodo zuria
Damot gale

Land use types
Fe
Cu
Zn
Mn
Fe
Cu
Zn
Mn

(mg kg⁻¹)
(mg kg⁻¹)

Enest-coffee
172.20a
6.33a
12.51a
143.67a
146.50a
3.62a
11.17a
142.40a

Crop land
182.20b
0.31b
12.77a
143.22b
157.70b
0.23b
11.84b
140.20a

Grazing
177.00c
6.15c
11.97b
136.39b
149.40c
0.80c
11.31b
137.80b

Mean
177.06
4.26
12.41
107.76
151.20
2.05
11.44
140.13

CV (%)
9.34
7.80
11.49
14.67
10.8
8.4
7.90
12.70

LSD (0.05)
1.64
3.32
0.42
0.47
7.10
1.88
0.40
0.78

Damot sore
Boloso sore

Enest-coffee
123.30a
2.86a
10.10a
132.50a
97.30a
3.93a
9.58a
116.50a

Crop land
129.40b
0.80b
10.70b
147.30b
101.70b
1.25b
8.98b
123.80b

Grazing
125.00c
2.50c
10.30c
139.00c
99.50c
2.20c
9.40a
122.60c

Mean
125.90
2.05
10.36
139.60
99.50
2.26
9.32
122.46

CV (%)
7.42
8.40
9.40
10.89
9.40
7.20
12.60
12.70

LSD (0.05)
1.30
1.74
0.48
0.52
4.30
1.89
0.17
0.68

4. Conclusions

The physical and chemical properties of soils in the study area vary from land use types and location. The enset coffe land system and grazing land were medium to higher in values, OC, total N and available P, CEC, exchangeable bases, and micronutrients content especially on the surface layer; this might be due to coarser texture of the soil, and the magnitudes of exchangeable Ca and Mg in land use types were rated as low to medium for Ca and medium to high for Mg. Although it is clayey in texture and relatively better in available P, crop land was lower in soil nutrients with lower pH which has become limiting for crop production in all locations. Therefore, it is suggested that besides physical and biology conservation practices, controlled grazing or cut and carry system and integrated soil fertility management techniques are recommended to improve productivity of acidic soils of the study area.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Authors’ Contributions

Mesfin Kassa, Fassil Kebede, and Wassie Haile contributed equally to this study.

Acknowledgments

The authors acknowledge the staff members of Department of Plant Science, Wolaita Sodo University and Hawassa Research Center of Soil Laboratory, for providing us with the necessary support to conduct this study. This work was supported by Ethiopian Ministry of Education and Wolaita Sodo University.

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