Are all three components of conservation agriculture necessary for soil conservation in the Sudan Savanna?

Figures & data

Table 1. Physical properties of the soil from the experimental site.

			Particle size distribution					Volumetric water content
	Depth	Coarse fragment >2 mm	C. Sand 0.2–2	F. Sand 0.02–0.2	Silt 0.002–0.02	Clay < 0.002	Bulk density	pF 1.6	pF 2.0	pF 2.5	pF 3.0	pF 3.2	pF 3.8	PF 4.2
Horizon	(cm)	(% weight)	(% weight of fine earth)				(Mg m^–3)	(%)
Ap	0–5	7.3	31.5	49.8	8.5	10.2	1.6	24.2	19.5	15.9	12.3	10.7	6.9	5.4
A	5–25	16.4	30.5	44.0	6.9	18.6	1.7	23.3	20.3	16.7	14.0	13.0	10.2	8.8
Btw	25–58	23.6	20.5	36.0	9.9	33.7	1.4	28.6	25.2	21.6	18.5	17.5	14.3	12.9
Btwc	58–73	44.1	22.3	39.5	7.2	31.1	1.5	28.4	25.3	21.4	17.5	16.3	13.2	11.8
Bmv	73–95+	–	–	–	–	–	–	–	–	–	–	–	–	–

C: coarse; F: fine. – : Soil sample could not be taken from Bmv horizon because it was consolidated.

Table 2. Chemical properties of the soil from the experimental site.

								Exchangeable bases
					OC	TN		Ca	Mg	K	Na	Al		EBS^b	Bray-1 P
Horizon	Depth (cm)	pH (H2O, 1:5)	pH (KCl, 1:5)	EC (mS m^–1)	(g kg^–1)		C/N^a	(cmolc kg^–1)					CEC	(%)	(mgP kg^–1)
Ap	0–5	5.5	4.3	2.8	4.4	0.5	9.8	1.2	0.4	0.0	0.0	0.0	1.5	100	1.8
A	5–25	5.1	4.1	4.2	2.7	0.3	8.6	1.3	0.4	0.0	0.0	0.2	2.0	92	1.0
Btw	25–58	5.2	4.2	2.5	2.5	0.4	7.1	1.7	0.6	0.0	0.0	0.4	5.0	86	0.5
Btwc	58–73	5.2	4.2	2.9	2.2	0.3	6.9	1.5	0.6	0.1	0.0	0.3	4.6	88	0.7
Bmv	73–95+	–	–	–	–	–	–	–	–	–	–	–	–	–	–

EC: electrical conductivity; OC: organic carbon content; TN: total nitrogen content; CEC: cation exchange capacity; EBS: effective base saturation.

^aRatio of OC to TN; ^bratio of exchangeable (Ca + Mg + K + Na) to exchangeable (Ca + Mg + K + Na + Al) defined in IUSS Working Group WRB (2015). – : Soil sample could not be taken from Bmv horizon because it was consolidated.

Figure 1. Photos of a wolf spider (top) and soil surfaces with the holes made by termites (center) and a wolf spider (bottom).

Bars represent 2 cm.

Table 3. Three-year average of annual soil loss, runoff coefficient, and sediment concentration for each treatment.

	Soil loss	Runoff coefficient	Sediment concentration
	(Mg ha^‒1 yr^‒1)	(%)	(g L^–1)
CNTRL	4.9^a	27.9^a	3.0^a
MT+CRM	2.3^b	18.8^b	2.2^a
CA_VB	2.0^b	17.5^b	2.1^a

Mean values with different letters are significantly different between treatments (P < 0.05).

Figure 2. Temporal distribution of rainfall and cumulative soil losses for 2013–2015.

Arrows represent the sowing date in each year.

Table 4. Biomass of crop residues retained in the field after harvesting.

	MT+CRM	CA_VB
	Sorghum stover (Mg ha^–1)	Sorghum stover	Velvet bean residue (Mg ha^–1)	Total
2012	2.4^a	1.7	1.3	3.0^a
2013	2.0^a	1.8	0.7	2.5^a
2014	2.3^a	2.0	1.0	3.0^a

Mean values with the same superscript letter are not significantly different between treatments (P ≥ 0.05).

Figure 3. Soil permeability of matrix soils in the CNTRL and MT+CRM plots and of soils with holes made by termites and wolf spiders in the MT+CRM plots.

Figure 4.  S in matrix soils of the CNTRL and MT+CRM plots and in soils with wolf spider and termite holes. S is the parameter called sorptivity that governs the early stage of water infiltration – an important parameter for water capture in semi-arid dryland systems.

Error bars indicate standard error. Mean values with different letters are significantly different (P < 0.05).

IUSS Working Group WRB 2015: World Reference Base for Soil Resources 2014, update 2015. World Soil Resources Reports No. 106. FAO, Rome.

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