3.1. Soil physical Properties
Most of the soil physical properties (bulk density, soil moisture content, and sand and clay textural class) under investigation exhibited a significant mean difference (P = 0.002*) across the different land use of the study sites, as indicated in Table 1. Among these, the mean bulk density of the open area is much higher than the other land uses. This might be due to higher compaction by livestock and human disturbance. This is in line with the finding of Endale (2016) Lemma, Menfes and Fantaw (2015), Demelash and Stahr (2010), which states that open areas experience significantly higher bulk density across compared to different land use due to differential treatment and management practices. In contrast, the finding of Abdelkadir and Yimer (2011) stated that bulk density does not vary under different land uses and does not show a significant mean difference.
From the soil particle size point of view, the overall percentage of sand (p = 0.011*) and clay (p = 0.038*) shows a significant difference across the different land uses at 0.05 level of significance respectively (Table 1). In view of this, the whole study area is dominated by sandy fractions followed by silt. However, comparatively there is a great difference in the mean percentage of soil minerals among the land uses. The soil of the protected area was dominated by sand (63.333 ± 5.993), followed by silt (18.667 ± 4.372a) and clay (18.000 ± 2.633b). Even though the results of multiple comparisons categorized statistically in a similar group, numerically, the mean percentage fraction of sand in open areas (50.000 ± 3.759a) is relatively very higher than that of closed are one (43 ± 2.113) and closed area two (41.333 ± 5.258). The relative dominance of the sandy fraction might be the result of selective removal of the fine fraction by runoff and deposition of sandy from the upper slope of area and from adjacent open area. This is consistent with the study of Brady and Weil (2002), Woldamlak (2003), and Sandor et al. (1986), who stated that pedagogical processes like erosion and deposition of soil particles affect the soil particle size.
Table 1
Mean value (+ standard error) of selected soil physical parameters across the study area.
Study Sites
|
Soil Parameter
|
BD (%)
|
MC (%)
|
% Sand
|
% Clay
|
% Silt
|
Closed Area1
|
0.950 ± 0.026a
|
26.855 ± 1.382a
|
43.000 ± 2.113a
|
26.333 ± 2.275a
|
30.667 ± 0.989a
|
Closed Area2
|
0.973 ± 0.037a
|
26.583 ± 1.568a
|
41.333 ± 5.258a
|
28.333 ± 1.745a
|
30.333 ± 3.947a
|
Protected Area
|
0.955 ± 0.030a
|
17.798 ± 1.915c
|
63.333 ± 5.993b
|
18.000 ± 2.633b
|
18.667 ± 4.372a
|
Open Area
|
1.145 ± 0.047b
|
7.770 ± 2.127b
|
50.000 ± 3.759a
|
24.000 ± 2.921b
|
26.000 ± 2.309a
|
P-value
|
0.002*
|
0.000*
|
0.011*
|
0.038*
|
0.053
|
* The mean difference is significant at the 0.05 level
|
In other words, the protected area, closed area one, and two have comparable mean of bulk density, which is the result of relatively low disturbance by livestock and human activity.
The soil moisture content is another physical parameter under investigation, which varies and exhibits significant mean difference (p = 0.000*) across the land uses. Accordingly, open area has lower moisture (7.770 ± 2.127b) followed by protected area, closed area two, and one, respectively. This is probably due to low soil organic matter content, lower vegetation cover, and dominance of sandy soil, which is consistent with the findings of Abdelkadir and Yimer (2011).
The overall result of correlation analysis (indicated in Table 2 below) showed that there is a strong positive relationship (r = 0.563**) between bulk density and pH at 0.01 significance level, while it showed a strong negative relationship with total nitrogen (r = -0.502*), organic carbon/soil organic matter (r = − 0.518**), and a very strong negative relationship with moisture content (r = -0.759**) at 0.01 and 0.05 significance levels, respectively. This was also in line with the findings of Pravin et al. (2013) and Ahad et al. (2015).
The result of one-way ANOVA also shows that the soil moisture of the closed area one (26.855 ± 1.382) and two (26.583 ± 1.568) were statistically homogenous and difficult to differentiate, while the difference was recognizable across protected area (17.798 ± 1.915) and open area (7.770 ± 2.127). However, numerically, there is a distinct difference in moisture content between closed area one and two. The high soil moisture content of closed area one and two is the result of high vegetation diversity, which has the potential to trap runoff as a result of infiltration through the help of their root system and low evaporation rate as a result of high canopy cover. The open area has relatively very low moisture content compared to other land uses. This is probably due to differences in organic matter content, high bulk density, overgrazing, and unsustainable land use and management (Maitima et al., 2009), which have great influence on the amount of water infiltrated and added to the soil profile.
Table 2
The results of binary correlation among the different physicochemical parameters under investigation in the study area
|
|
pH
|
EC
|
OC
|
SOC
|
Ava_P
|
Ava_K
|
TN
|
CEC
|
Ex_Ca
|
Ex_Mg
|
Ex_K
|
% sand
|
% clay
|
% silt
|
MC
|
BD
|
pH
|
Pearson Corr.
|
1
|
0.054
|
− .545**
|
− .545**
|
− .748**
|
-0.264
|
-0.305
|
-0.191
|
.447*
|
-0.286
|
-0.202
|
-0.355
|
.499*
|
0.162
|
-0.335
|
.563**
|
|
p-value
|
|
0.803
|
0.006
|
0.006
|
0
|
0.213
|
0.147
|
0.372
|
0.028
|
0.176
|
0.345
|
0.089
|
0.013
|
0.45
|
0.11
|
0.004
|
EC
|
Pearson Corr.
|
|
1
|
-0.12
|
-0.12
|
-0.113
|
.424*
|
0.078
|
0.033
|
-0.083
|
0.396
|
-0.194
|
-0.077
|
0.039
|
0.088
|
0.004
|
0.127
|
|
p-value
|
|
|
0.577
|
0.577
|
0.599
|
0.039
|
0.719
|
0.878
|
0.701
|
0.055
|
0.364
|
0.722
|
0.855
|
0.684
|
0.986
|
0.554
|
OC
|
Pearson Corr.
|
|
|
1
|
1.000**
|
0.216
|
0.088
|
0.265
|
.429*
|
0.212
|
.436*
|
0.167
|
-0.234
|
0.166
|
0.232
|
.595**
|
− .518**
|
|
p-value
|
|
|
|
0
|
0.311
|
0.681
|
0.211
|
0.036
|
0.32
|
0.033
|
0.435
|
0.272
|
0.437
|
0.276
|
0.002
|
0.009
|
SOM
|
Pearson Corr.
|
|
|
|
1
|
0.216
|
0.088
|
0.265
|
.429*
|
0.212
|
.436*
|
0.167
|
-0.234
|
0.166
|
0.232
|
.595**
|
− .518**
|
|
p-value
|
|
|
|
|
0.311
|
0.681
|
0.211
|
0.036
|
0.32
|
0.033
|
0.435
|
0.272
|
0.437
|
0.276
|
0.002
|
0.009
|
Ava_P
|
Pearson Corr.
|
|
|
|
|
1
|
0.127
|
0.262
|
0.037
|
− .599**
|
0.083
|
0.104
|
0.357
|
− .479*
|
-0.18
|
0.098
|
-0.271
|
|
p-value
|
|
|
|
|
|
0.554
|
0.215
|
0.865
|
0.002
|
0.7
|
0.628
|
0.087
|
0.018
|
0.4
|
0.649
|
0.2
|
Ava_K
|
Pearson Corr.
|
|
|
|
|
|
1
|
.419*
|
0.23
|
0.023
|
0.113
|
-0.152
|
-0.127
|
-0.006
|
0.201
|
0.35
|
-0.313
|
|
p-value
|
|
|
|
|
|
|
0.041
|
0.279
|
0.916
|
0.599
|
0.478
|
0.555
|
0.976
|
0.347
|
0.094
|
0.137
|
TN
|
Pearson Corr.
|
|
|
|
|
|
|
1
|
0.385
|
-0.095
|
-0.056
|
0.02
|
0.095
|
0.014
|
-0.157
|
.464*
|
− .502*
|
|
p-value
|
|
|
|
|
|
|
|
0.063
|
0.659
|
0.793
|
0.928
|
0.66
|
0.949
|
0.464
|
0.022
|
0.012
|
CEC
|
Pearson Corr.
|
|
|
|
|
|
|
|
1
|
0.337
|
0.314
|
-0.026
|
0.002
|
0.018
|
-0.018
|
0.194
|
0.056
|
|
p-value
|
|
|
|
|
|
|
|
|
0.107
|
0.136
|
0.904
|
0.992
|
0.932
|
0.935
|
0.365
|
0.795
|
Ex_Ca
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
1
|
-0.047
|
− .465*
|
− .619**
|
.628**
|
.471*
|
0.219
|
0.139
|
|
p-value
|
|
|
|
|
|
|
|
|
|
0.829
|
0.022
|
0.001
|
0.001
|
0.02
|
0.305
|
0.516
|
Ex_Mg
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
1
|
0.079
|
0.067
|
0.03
|
-0.127
|
0.271
|
-0.018
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
0.715
|
0.756
|
0.889
|
0.555
|
0.2
|
0.934
|
Ex_K
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
|
1
|
.418*
|
-0.292
|
− .419*
|
-0.202
|
-0.117
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
|
0.042
|
0.166
|
0.042
|
0.343
|
0.587
|
% sand
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
|
|
1
|
− .829**
|
− .902**
|
-0.383
|
0.203
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
|
|
0
|
0
|
0.065
|
0.341
|
% clay
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
.507*
|
0.324
|
-0.145
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0.011
|
0.123
|
0.499
|
% silt
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
0.341
|
-0.202
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0.103
|
0.344
|
Moisture
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
− .759**
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0
|
Bulk density
|
Pearson Corr.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1
|
|
p-value
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed).
|
The result of ANOVA analysis also shows that the mean percentage fraction of clay across the area of investigation is significantly different (p = 0.038*). However, the silt fraction across land use is not significantly different (0.053), although numerically they differ (Table 2). Closed area two recorded the highest clay fraction followed by closed area one, open, and protected area, respectively.
3.2. Soil chemical properties
Among the selected parameters for analysis of soil chemical dynamics, pH (p = 0.022*), soil organic matter (p = 0.005*), and exchangeable calcium (p = 0.000*), and potassium (p = 0.000*) showed significant mean differences across the different land uses of the study area, while electric conductivity, available potassium, available phosphorus, total nitrogen, cation exchange capacity, and exchangeable magnesium were insignificant (Table 3). The mean pH value of the open area (8.04 ± 0.034b) was significantly very higher than that of the enclosed area two (7.94 ± 0.058ab), closed area one (7.79 ± 0.059ab), and protected area (7.75 ± 0.100a). The higher mean value of pH in open area might be related to the relatively higher leaching of nutrients and lower soil organic matter content, which is in line with the findings of Umer and Sinore (2019).
The mean value of soil organic matter is significantly varied across the study area, and it was very high in the closed area one followed by the closed area two, although Tukey's homogeneity test shows there is no mean difference between the two areas. This is the result of several factors, such as vegetation (Yimer, 2007; Finzi et al., 1998), and management (Yang and Wander, 1999). The findings of this research are also complementary to the aforementioned studies. According to the study of Buschiazzo et al. (2004), soil organic matter highly depends on clay and silt content when vegetation is dense and uniform, and the coverage is sparse and heterogeneous. The protected area also has higher soil organic matter than the open area. The reason for this variation may be the result of differences in vegetation diversity and composition, and the intensity of disturbance they face from the external environment, mainly livestock and charcoal burning activity carried out by the local community.
The result of multiple comparisons using Tukey's HSDa and homogeneity test showed that there was no statistically significant mean difference in available soil nutrients across the four study sites. However, there is a slight variation in terms of available soil nutrients in the area. Accordingly, the protected area was characterized by having high available phosphorus (9.70 ± 3.261a) and total nitrogen (0.28 ± 0.064a), while available potassium was very low (1062.29 ± 110.018a) compared to other land uses. Followed by protected area, the closed area revealed a high concentration of phosphorus (5.88 ± 1.374a), potassium (2806.46 ± 1478.592a), and total nitrogen (0.27 ± 0.091a).
Table 3
The mean (+ standard error) value of selected soil chemical parameters across the study area
study sites
|
Soil chemical parameters
|
pH
|
EC
|
SOC
|
Av. P
|
Av. K
|
TN
|
CEC
|
Ex. Ca
|
Ex. Mg
|
Ex. K
|
Closed Area 1
|
7.79 ± 0.059ab
|
494.17 + 87.270a
|
3.153 + 0.185b
|
5.88 + 1.374a
|
2806.46 + 1478.592a
|
0.27 + 0.091a
|
22.50 + 1.647a
|
37.33 + 2.404b
|
5.67 + 0.667a
|
1.77 + 0.159a
|
Closed Area 2
|
7.94 ± 0.058ab
|
357.83 ± 23.913a
|
2.68 ± 0.507b
|
3.87 ± 0.909a
|
1159.69 ± 131.934a
|
0.26 ± 0.051a
|
19.23 ± 1.522a
|
40.50 ± 1.408b
|
4.67 ± 0.615a
|
1.31 ± 0.079a
|
Protected Area
|
7.75 ± 0.100a
|
314.50 ± 13.873a
|
2.41 ± 0.418ab
|
9.70 ± 3.261a
|
1062.29 ± 110.018a
|
0.28 ± 0.064a
|
17.73 ± 2.056a
|
22.83 ± 2.626a
|
4.50 ± 1.176a
|
4.24 ± 0.677b
|
Open area
|
8.04 ± 0.034b
|
484.17 ± 99.993a
|
1.19 ± 0.106a
|
3.07 ± 1.949a
|
1203.02 ± 191.899a
|
0.13 ± 0.070a
|
18.23 ± 1.982a
|
34.83 ± 2.330b
|
3.83 ± 0.654a
|
1.64 ± 0.065a
|
P - value
|
0.022*
|
0.185
|
0.005*
|
0.140
|
0.323
|
0.432
|
0.274
|
0.000*
|
0.472
|
.000*
|
* the mean difference is statistically significant at 0.05 level; Electrical conductivity (EC in µS/cm), Soil Organic Matter (SOM) in %, Available phosphorus (Av. P) in ppm, Available potassium (Av. K) in ppm, Total Nitrogen (TN) in %, Cation exchange capacity (CEC) in meq/100 g, Exchangeable calcium in meq/100 g, exchangeable magnesium (ex. Mg) in meq/100 g and exchangeable potassium (Ex. K) in meq/100 g
|
3.3. Soil Macrofauna Diversity and Biomass distribution
Macrofauna diversity analysis was conducted across the different land uses (protected area, open area, closed area one, and two). The results of the diversity index showed that the closed area one have a higher diversity of soil organisms compared to other land uses, as indicated in Table 4 below. On top of this, the abundance (32.69%) and species richness (30.95%) were also higher in the closed area one followed by closed area two, which have species richness and abundance of 26.19%, and 24.16%, respectively. These were probably the result of the difference in age of establishment of closed area (i.e., 15 and 12 years for closed area one and two, respectively), its management, and low carbon to nitrogen ratio recoded in the area. Furthermore, flooding of their burrows by excessive rainfall during the seasons of data collection. The distribution pattern of soil organisms was also more even (0.74) in the closed area one (Table 4), followed by closed area two and protected areas.
Table 4
The diversity, evenness, abundance and species richness of soil organisms across the different land use.
study area
|
H'
|
Evenness (E)
|
Abundance
|
richness
|
Closed Area one
|
1.90
|
0.74
|
303
|
13
|
Closed Area two
|
1.14
|
0.49
|
187
|
10
|
Protected Area
|
1.30
|
0.54
|
224
|
11
|
Open Land
|
0.89
|
0.43
|
213
|
8
|
Page 11 |
The lowest diversity and species richness of soil organisms was documented in closed area two (0.89) and open area (1.14), which had more species richness and abundance compared to closed area two.
The analysis of the biomass of soil organisms was also performed across the different land uses of the study area. Accordingly, the highest record of biomass per meter square (11.4) of soil organisms was obtained in Open followed by the protected area (6.18).Even though the mean difference of biomass across the land uses was observable from Table 7 below, it was not statistically significant at alpha of 0.05 and 0.01. A possible reason for the higher biomass of soil organisms in protected area than others was the availability of high total nitrogen, low pH (7.75), and low carbon to nitrogen ratio (5.04) relative to the other land uses.
Table 3
Biomass of soil organisms across the different land uses in the study area
Common names of Soil Organisms
|
Biomass of soil organisms in gram/m2
|
PA
|
CA1
|
CA2
|
OA
|
Nairobi fly
|
0.10
|
0.10
|
0.10
|
0.00
|
Ant
|
0.00
|
0.10
|
0.13
|
0.13
|
Beetles
|
0.10
|
0.00
|
0.00
|
0.00
|
Butterfly larvae
|
0.30
|
0.00
|
0.00
|
0.00
|
Centipede
|
0.30
|
0.00
|
0.00
|
0.00
|
Cockroach
|
0.00
|
0.30
|
0.00
|
0.00
|
Earthworm 1
|
0.52
|
0.25
|
0.13
|
0.10
|
Earthworm 2
|
1.00
|
2.58
|
3.78
|
7.70
|
Earthworm 3
|
0.55
|
0.17
|
0.17
|
0.73
|
Insect larvae
|
0.30
|
0.20
|
0.00
|
0.25
|
Millipede
|
0.98
|
0.00
|
0.00
|
0.00
|
Soil bug
|
1.63
|
0.54
|
0.62
|
0.13
|
spider
|
0.20
|
0.10
|
0.00
|
0.10
|
larvae (arthropod)
|
0.00
|
0.10
|
0.20
|
0.00
|
Termite
|
0.10
|
0.00
|
0.00
|
0.00
|
Grasshopper
|
0.00
|
0.00
|
0.00
|
0.30
|
Earthworm 4
|
0.00
|
0.00
|
0.00
|
1.90
|
Unidentified
|
0.10
|
0.30
|
0.10
|
0.10
|
Total biomass
|
6.18
|
4.74
|
5.22
|
11.44
|
Where: PA- protected area CA1 – Closed area one CA2 – Closed area two OA - Open area |
Table 5
Biomass of soil organisms across the different land use in the study area
Common names of Soil Organisms
|
Biomass of soil organisms in gram/m2
|
Total Biomass
|
PA
|
CA1
|
CA2
|
OA
|
Nairobi fly
|
0.10
|
0.10
|
0.10
|
0.00
|
0.30
|
Ant
|
0.00
|
0.10
|
0.13
|
0.13
|
0.36
|
Beetles
|
0.10
|
0.00
|
0.00
|
0.00
|
0.10
|
Butterfly larvae
|
0.30
|
0.00
|
0.00
|
0.00
|
0.30
|
Centipede
|
0.30
|
0.00
|
0.00
|
0.00
|
0.30
|
Cockroach
|
0.00
|
0.30
|
0.00
|
0.00
|
0.30
|
Earthworm 1
|
0.52
|
0.25
|
0.13
|
0.10
|
1.00
|
Earthworm 2
|
1.00
|
2.58
|
3.78
|
7.70
|
15.06
|
Earthworm 3
|
0.55
|
0.17
|
0.17
|
0.73
|
1.62
|
Earthworm 4
|
0.00
|
0.00
|
0.00
|
1.90
|
1.90
|
Insect larvae
|
0.30
|
0.20
|
0.00
|
0.25
|
0.75
|
Millipede
|
0.98
|
0.00
|
0.00
|
0.00
|
0.98
|
Soil bug
|
1.63
|
0.54
|
0.62
|
0.13
|
2.92
|
spider
|
0.20
|
0.10
|
0.00
|
0.10
|
0.40
|
larvae (arthropod)
|
0.00
|
0.10
|
0.20
|
0.00
|
0.30
|
Termite
|
0.10
|
0.00
|
0.00
|
0.00
|
0.10
|
Grasshopper
|
0.00
|
0.00
|
0.00
|
0.30
|
0.30
|
Unidentified
|
0.10
|
0.30
|
0.10
|
0.10
|
0.60
|
Total biomass
|
6.18
|
4.74
|
5.22
|
11.44
|
27.58
|
Where: PA- protected area CA1 – Closed area one CA2 – Closed area two OA - Open area |