Influences of land-use types on soil organic carbon, total nitrogen and related soil properties in semi-arid area, Pretoria D.G. Talore, A. Hassen, Department of Animal and Wildlife Sciences, E. H. Tesfamariam, Department of Plant Production and Soil Science, University of Pretoria
Introduction Grassland soils have a great potential for carbon (C) sequestration. The storage of organic C of grasslands, however, depends on management regimes and previous land-use history. Carbon and nitrogen (N) sequestration potential of different land-use types varies according to management practices, but such information is limited in sub-Saharan Africa.
Aim •
To quantify the soil C and N stock and selected soil properties under various land-use types in the semi-arid agro-ecological zone of South Africa.
Cropland
Cultivated pasture land
Methodology Four different land-use types were considered for this study: Cropland (CL), cultivated pasture land (CPL), Leucaena sp. Plot (LP) and exclosure around Pretoria. Soil samples were collected at two depths (0-15 cm and 15-30 cm) from each land-use type, using four to five transects. The samples were collected using auger and were air dried and pulverized to pass through a 150-µm screen and analyzed for total C and N using a Carlo Erba NA1500 C/N analyzer (Carlo Erba Strumentazione, Milan, Italy) and other parameters following standard procedures. Exclosure
Leucaena plot
Results Figure 2 C and N concentration as affected by land-use types in Pretoria. Cultivated pasture land, CPL; Cropland, CL; Leucaena sp. plots, LP and Exclosure, Excl. Bars represent standard error of mean
Figure 1 Peak season aboveground net primary productivity as affected by land-use type in Pretoria, South Africa.
Cultivated pasture land, CPL; Cropland, CL; Leucaena plot, LP. SEM, standard error mean. Bars represent standard error of mean
Highlights Table 1 Soil organic C and total N stocks, C : N ratios and bulk density (mean ± SEM) for soil samples as affected by land-use type and soil depth in Hatfield, South Africa Fixed effects
C:N
•
Peak season aboveground net primary activity differed significantly between the land-use types.
(g cm-3)
•
All soil parameters considered in this study differed significantly between land-use types
•
The exclosure had higher C, N and C:N ratio, but lower bulk density (BD) and pH than LP, CPL and CL.
•
The major cations (Ca, Mg, K and Na) showed wide variations among land-use types
•
The top soil layer (0-15 cm) demonstrated lower BD and pH, but had higher C, N, Na and CEC than the lower 15-30 cm.
•
There was interaction effects between landuse type and soil depth only for C and N concentration.
•
The top 0-15 cm soil layer had generally higher C and N than the lower 15-30 cm layers, signifying their sensitivity to land-use types and soil depths. When potential C and N stock was estimated, the C sequestration rate was 1.41, 0.73, 0.40 and 0.33 Mg C ha-1 yr-1 in the LP, exclosure, CL and CPL while the corresponding values for N sequestration were 0.11, 0.05, 0.04 and 0.03 Mg N ha-1 yr-1.
SOC
Total N
Bulk density
( kg m-2)
(kg m-2)
CPL
2.03 ± 0.11c
0.16 ± 0.01d
12.65 ± 0.19b
1.47 ± 0.016a
CL
2.40 ± 0.13b
0.25 ± 0.01b
9.81 ± 0.23d
1.49 ± 0.020a
LP
2.26 ± 0.13bc
0.20 ± 0.01c
11.36 ± 0.23c
1.35 ± 0.018b
4.35 ± 0.12a
0.32 ± 0.01a
13.44 ± 0.21a
1.40 ± 0.020b
3.04 ± 0.09a
0.26 ± 0.01a
11.72 ± 0.15
1.40 ± 0.013b
0.09b
0.01b
11.91 ± 0.15
0.013a
Land-use type
Exclosure Soil depth (cm) 0–15 15–30
2.48 ±
0.21 ±
1.45 ±
Table 2 Partial ANOVA table showing degrees of freedom and F-values from restricted estimation of maximum likelihood analysis (at α=0.05) for soil organic carbon, total nitrogen concentration, carbon : nitrogen ratios, bulk density and soil chemical properties across land-use types (LU) and soil depths (SD) in Hatfield, Pretoria, South Africa Effects
parameters DF
SOC
TN
LU
1
102.36*** 66.77***
SD
3
33.53***
LU x SD
3
3.26*
C:N
52.4*** 10.16***
41.92*** 0.76NS
3.74*
BD
6.78**
Ca
Mg
K
Na
CEC
pH
EC
5.79**
9.41*
3.06*
6.28*
4.58*
2.85*
7.42***
1.66*
2.79*
3.27*
0.06NS •
0.00NS 0.25NS 0.15NS
0.18NS 2.71NS 0.33NS 0.13NS 1.45NS 0.15NS 0.29NS
0.52NS 0.08NS
Conclusion Land-use management practices geared towards integration of multipurpose tree species in suitable niches as well as animal exclusion from fragile soils would potentially improve C and N storage in semi-arid areas of South Africa.
Contact Abubeker Hassen, Department of Animal and Wildlife Sciences, university of Pretoria, email:
[email protected] or Eyob Tesfamariam, Department of Plant and Soils Sciences, University of Pretoria, Email:
[email protected]
Acknowledgements The authors gratefully acknowledge funding from the University of Pretoria, National Research Foundation, Dept. of Science and Technology and the European communities, 7th framework programme under the grant agreement No. 266018, ANIMALCHANGE project.
