Changes in soil organic carbon stocks and soil quality: land-use system effects in northern Ethiopia

Figures & data

Figure 1.  Location of the study area.

Table I. Mean soil properties (0–20 cm), standard error of means (SEM) and membership values (Q(Xi) of different land uses. OC: Soil organic carbon; N: total nitrogen; C/N: carbon-nitrogen ratio; Pav: available phosphorus; Kav: available potassium; BD: Bulk density; n: number of samples; CL: cultivated land; GL: grazing land; PA: plantation area (Eucalyptus); AE: area exclosure.

			Particle size distribution
Site	Land uses	Values	Sand (%)	Silt (%)	Clay (%)	Porosity (%)	pH (1:2.5 H2O)	OC %	N %	C/N ratio	Pav mg kg^−1	Kav mg kg^−1	BD g cm^−3
Maileba	CL (n = 5)	Mean	27.0	33.6	40.1	52.1	7.6	1.2	0.1	10.8	12.5	169.6	1.3
		SEM	2.9	1.7	3.3	0.0	0.2	0.1	0.0	1.0	2.4	14.4	0.0
		Q(Xi)					0.3	0.0	0.0	1.0	0.0	0.0	0.3
	GL (n = 4)	Mean	31.9	26.4	41.7	49.9	7.8	1.7	0.2	10.0	30.0	381.8	1.3
		SEM	2.4	2.0	3.2	0.0	0.3	0.2	0.0	1.6	11.5	30.9	0.0
		Q(Xi)					0.0	0.7	0.7	0.4	1.0	0.7	0.0
	PA (n = 3)	Mean	20.7	29.9	40.4	52.8	7.4	1.6	0.2	9.7	20.9	288.2	1.3
		SEM	1.1	1.8	2.7	0.2	0.2	0.3	0.0	1.0	2.1	30.5	0.2
		Q(Xi)					0.6	0.6	0.6	0.2	0.5	0.4	0.4
	AE (n = 3)	Mean	41.6	27.1	31.3	57.7	7.2	1.9	0.2	9.4	24.2	460.3	1.1
		SEM	3.9	1.8	3.1	0.1	0.1	0.2	0.0	0.2	2.6	125.2	0.1
		Q(Xi)					1.0	1.0	1.0	0.0	0.7	1.0	1.0
Gum Selassa	CL (n = 4)	Mean	41.8	27.8	30.3	54.6	7.5	1.0	0.1	10.8	17.1	191.5	1.2
		SEM	12.5	3.8	10.1	0.1	0.4	0.1	0.0	3.2	1.2	40.5	0.1
		Q(Xi)					0.0	0.9	1.0	0.9	1.0	0.0	1.0
	GL (n = 3)	Mean	48.4	37.5	14.1	53.6	8.3	1.0	0.1	11.1	14.1	194.1	1.2
		SEM	1.2	0.7	1.5	0.1	0.5	0.2	0.0	1.9	1.3	48.9	0.1
		Q(Xi)					1.0	1.0	0.0	1.0	0.1	0.0	0.7
	PA (n = 3)	Mean	49.0	29.1	21.9	49.8	7.8	0.8	0.1	9.1	13.7	270.3	1.3
		SEM	6.2	2.7	1.9	0.1	0.6	0.1	0.0	0.4	1.4	97.8	0.1
		Q(Xi)					0.6	0.0	0.0	0.0	0.0	1.0	0.0

Table II. Result of general linear model analysis for major soil properties under four soil depths obtained from different land uses and two sites (p<0.05).

	Land uses		Site		Soil depth
Soil property	F (df=3)	P	F (df=1)	P	F (df=3)	P
OC (%)	1.56	0.204	31.48	0.000*	4.27	0.007*
N (%)	1.07	0.368	6.57	0.012*	1.00	0.399
Pav (mg kg^−1)	4.33	0.007*	3.17	0.078	0.36	0.784
Kav (mg kg^−1)	0.19	0.903	1.00	0.323	2.68	0.056
BD (g cm^−3)	2.66	0.053*	3.95	0.050*	10.29	0.000*
C/N ratio	1.35	0.263	5.11	0.026*	0.11	0.956
^* Indicates significant differences at p<0.05. For abbreviations see Table I.

Table III. Results for Tukey paired wise multiple comparison test of soil properties for different land uses and soil depths (p<0.05).

Soil property	Significant paired wise comparison	p-value
	Land uses
Pav (mg kg^−1)	CL and GL	0.003
BD (g cm^−3)	AE and GL	0.047
	Depths
OC (%)	0–20 cm and 60–80 cm	0.006
BD (g cm^−3)	0–20 cm and 60–80 cm	0.000
	20–40 cm and 60–80 cm	0.000
	40–60 cm and 60–80 cm	0.005
For abbreviations see Table I.

Table IV. Depth- wise distribution of mean (± SEM) of soil properties under different land uses at Maileba and Gum Selassa sites.

		Maileba				Gum Selassa
Soil Property	Depth	AE	CL	GL	PA	CL	GL	PA
OC (%)	0–20	1.9±0.2	1.2±0.1	1.7±0.2	1.6±0.3	1.0±0.1	1.0±0.2	0.8±0.1
	20–40	1.7±0.2	1.2±0.2	1.6±0.1	1.5±0.3	0.8±0.1	0.8±0.2	0.8±0.2
	40–60	1.4±0.4	1.5±0.2	1.0±0.5	0.7±0.1	0.8±0.3	0.8±0.2	0.7±0.2
	60–80	0.5±0.1	1.1±0.3	1.0±0.3	0.7±0.1	0.7±0.2	0.7±0.2	0.8±0.0
N (%)	0–20	0.2±0.0	0.1±0.0	0.2±0.0	0.2±0.0	0.1±0.0	0.1±0.0	0.1±0.0
	20–40	0.2±0.0	0.1±0.0	0.2±0.0	0.2±0.0	0.1±0.0	0.1±0.0	0.1±0.0
	40–60	0.1±0.0	0.1±0.0	0.1±0.3	0.1±0.0	0.1±0.0	0.1±0.0	0.1±0.0
	60–80	0.1±0.0	0.1±0.0	0.1±0.0	0.1±0.0	0.1± 0.0	0.1±0.0	0.1±0.0
C/N ratio	0–20	9.4±0.2	10.8±1.1	10.0±1.6	9.7±1.0	10.8±3.3	11.1±1.9	9.1±0.4
	20–40	9.6±0.4	13.7±1.8	9.8±1.3	9.7±0.6	7.8±0.5	9.5±1.5	7.7±0.3
	40–60	10.7±1.4	11.1±0.6	8.8±3.8	10.5±1.0	7.5±0.4	10.0±1.7	8.8±1.6
	60–80	10.3±2.2	9.9±1.3	15.6±1.2	8.5±0.7	9.6±0.8	10.4±3.0	7.9±0.2
Pav (mg kg^−1)	0–20	24.2±2.6	12.5±2.4	30.0±11.5	20.9±2.1	17.1±1.2	14.1±1.1	13.7±1.2
	20–40	21.6±1.3	8.9±2.8	31.9±19.2	22.8±0.9	16.3±0.6	17.3±1.2	14.4±2.1
	40–60	19.3±3.2	14.8±2.3	28.5±18.8	14.5±1.1	14.2±1.6	17.6±3.6	15.8± 3.0
	60–80	14.6±1.8	11.0±3.1	37.1±26.7	13.8±1.1	13.5±2.6	13.8±2.7	12.5± 0.8
Kav (mg kg^−1)	0–20	460.3±216.8	169.6±42.2	381.8±63.1	288.2±52.8	191.5±40.5	194.1±84.7	270.3±69.4
	20–40	221.0±59.4	130.4±27.0	203.9±30.8	231.7±74.6	139.4±46.0	181.7±87.8	93.1±17.4
	40–60	215.8±79.6	111.1±31.6	331.8±78.2	180.4±46.9	170.1±45.2	179.5±84.1	90.7±23.0
	60–80	89.8±28.0	127.9±56.1	143.2±51.4	163.8±83.3	168.3±39.1	187.6±90.1	190.6±91.2
BD (g cm^−3)	0–20	1.1±0.1	1.1±0.0	1.3±0.0	1.3± 0.2	1.2±0.1	1.2±0.0	1.3±0.0
	20–40	1.2±0.0	1.3±0.1	1.4±0.0	1.3±0.1	1.3±0.1	1.3±0.1	1.4±0.1
	40–60	1.2±0.1	1.3±0.0	1.4±0.0	1.3±0.1	1.5±0.1	1.4±0.1	1.4±0.1
	60–80	1.4±0.1	1.5±0.0	1.53± 0.1	1.4±0.1	1.6±0.1	1.7±0.1	1.5±0.1
For abbreviations see Table I.

Table V. Profile level carbon stocks at different land use types and two sites.

		Maileba			Gum Selassa
Soil depths (cm)	Land uses	Mean SOC pool (Mg ha^−1)	Area (ha)	Total SOC stocks (Mg)	Mean SOC pool (Mg ha^−1)	Area (ha)	Total SOC stocks (Mg)
0–20	AE	43(a)	13.6	585
	PA	36(ab)	50.8	1829	17(a)	18.5	315
	GL	33(ab)	188.0	6204	19(a)	338.7	6435
	CL	26(b)	1083.4	28–168	21(a)	1877.3	39–423
20–40	AE	31(a)	13.6	422
	PA	32(a)	50.8	1626	17(a)	18.5	315
	GL	32(a)	188.0	6016	16(a)	338.7	5419
	CL	29(a)	1083.4	31–419	17(a)	1877.3	31–914
40–60	AE	31(a)	13.6	422
	PA	15(b)	50.8	762	16(a)	18.5	296
	GL	26(a)	188.0	4888	16(a)	338.7	5419
	CL	35(a)	1083.4	37–919	22(a)	1877.3	41–301
60–80	AE	12(b)	13.6	163
	PA	17(ab)	50.8	864	19(a)	18.5	352
	GL	42(a)	188.0	7898	17(a)	338.7	5758
	CL	28(ab)	1083.4	30–335	19(a)	1877.3	35–669
Total carbon stock (Mg C)				159–516			172–615
Values of SOC pool followed by the same letter (in parentheses) on a column under each soil depths are not statistically different at p<0.05. For abbreviations see Table I.

Figure 2.  Weight for soil quality indicators (Wi) and soil quality index (SQI) for different land uses at Maileba (a and b) and at Gum Selassa (c and d), respectively. BD: bulk density; pH: soil pH; P: available P; K: available K; C/N: carbon-nitrogen ratio; N: total nitrogen, OC: soil organic carbon; CL: cultivated land; GL: grazing land; PA: plantation area (Eucalyptus); AE: area exclosure.