Function of geophagy as supplementation of micronutrients in Tanzania

Figures & data

Figure 1  Appearance of the edible soil sticks (pemba) in Tanzania. From left to right: Pr1, Pr2, Pr3, Pr4, Pr5, Pw1, Pw2 and Pw3. The coin on the right is 2 cm in diameter.

Table 1 Color and shape of the pemba

Sample		Color	Length (cm)	Width (cm)	Volume (cm^3)	Weight (g)	Density (g cm^−3)	Location^†
Pr1	2.5YR5/6	Bright reddish brown	4.8	1.8	11.4	10.4	0.9	Mpanda
Pr2	5YR5/6	Bright reddish brown	8.0	2.0	25.1	39.0	1.6	Dar es Salaam
Pr3	5YR6/8	Orange	7.4	2.3	30.3	39.8	1.3	Kigoma
Pr4	5YR5/6	Bright reddish brown	6.8	1.1	6.8	13.1	1.9	Kigoma
Pr5	5YR5/8	Bright reddish brown	7.2	2.0	23.0	33.0	1.4	Morogoro
Pw1	5Y8/1	Light gray	4.9	1.4	6.9	7.9	1.1	Mpanda
Pw2	7.5Y8/1	Light gray	4.1	1.4	6.6	7.4	1.1	Dar es Salaam
Pw3	7.5YR8/2	Light gray	5.9	2.1	20.2	25.7	1.3	Kigoma
Average (Pr)			6.8	1.8	19.3	27.1	1.4
Average (Pw)			5.0	1.6	27.1	13.7	1.2
Average (Total)			6.1	1.8	16.3	22.0	1.3
^†Location of the local market where the samples were purchased.

Table 2 Texture and mineralogy of the pemba and soil samples

Sample	Sand (%)	Course sand (%)	Fine sand (%)	Silt (%)	Clay (%)	Textural class	Clay mineralogy
Pemba
Pr1	28	12	16	26	46	Heavy clay	Kt>>It>Qz, He
Pr2	29	12	17	17	54	Heavy clay	Kt>>He
Pr3	31	16	15	32	38	Light clay	Kt>>It, Qz, He, Ge
Pr4	31	14	18	30	39	Light clay	Kt>>It>Qz, He
Pr5	34	15	19	27	39	Light clay	Kt>It>>Qz, He, Ge
Pw1	3	2	1	35	62	Heavy clay	Kt
Pw2	8	6	2	32	60	Heavy clay	Kt
Pw3	11	8	2	43	46	Heavy clay	Kt>>It, Qz
Average (Pr)	31	14	17	26	43	Light clay
Average (Pw)	7	5	2	37	56	Heavy clay
Average (Total)	22	11	11	30	48	Heavy clay
Soil
Average	56	41	15	10	33	Sandy clay	Kt>>It, Vt, He, Ge
Maximum	91	72	30	24	69	Heavy clay
Minimum	16	11	5	2	6	Loamy Sand
CV (%)	46	52	55	66	66
CV, coefficients of variation; Ge, goethite; He, hematite; It, illite; Kt, kaolinite. Qz, quartz; Vt, vermiculite.

Table 3 Chemical characteristics of the pemba and soil samples

Sample	pH	EC (µS cm^−1)	Total C (g kg^−1)	Exchangeable bases				CEC
				Ca	Mg	Na	K
				(cmolc kg^−1)
Pemba
Pr1	5.0	89	3.8	1.04	1.33	0.23	0.28	12.6
Pr2	5.4	54	0.6	3.70	1.58	0.16	0.11	9.5
Pr3	4.9	41	2.0	0.92	2.52	0.09	0.19	13.1
Pr4	4.8	124	5.0	1.23	3.76	0.84	0.27	13.8
Pr5	4.7	200	0.2	1.23	2.33	0.83	0.29	13.5
Pw1	5.4	78	3.3	6.01	4.41	0.33	0.20	10.5
Pw2	4.8	58	2.9	2.99	1.71	0.10	0.13	8.0
Pw3	4.1	230	2.4	2.28	1.46	0.13	0.13	7.6
Average (Pr)	5.0	102	2.3	1.63	2.30	0.43	0.23	12.5
Average (Pw)	4.8	122	2.8	3.76	2.52	0.19	0.15	8.7
Average (Total)	4.9	109	2.5	2.43	2.39	0.34	0.20	11.1
Soil
Average	5.2	80	8.1	2.46	1.80	0.03	0.79	13.3
Maximum	5.4	210	35.9	11.57	11.68	0.10	2.71	33.5
Minimum	5.0	26	2.1	0.07	0.12	0.01	0.00	2.1
CV (%)	2	72	107	140	163	81	136	72
CEC, cation exchange capacity; CV, coefficients of variation; EC, electrical conductivity.

Table 4 Total concentration of eight nutrients in the pemba

Sample	Fe	Mg	Mn	Ca	Zn	Cu	Co	Ni
	(g kg^−1)		(mg kg^−1)
Pemba
Pr1	127	2.9	683	332	64	95.3	39.8	20
Pr2	98	0.5	135	774	56	26.2	16.4	40
Pr3	147	4.0	994	345	78	118.2	62.9	23
Pr4	151	4.9	1107	429	89	84.0	64.5	23
Pr5	153	4.1	1097	400	80	70.2	65.0	21
Pw1	15	0.7	173	684	54	101.8	46.1	80
Pw2	17	0.4	90	662	20	82.3	30.9	33
Pw3	24	0.5	57	513	242	41.5	16.4	98
Average (Pr)	135	3.3	803	456	73	79	50	26
Average (Pw)	19	0.6	106	620	105	75	31	70
Average (Total)	92	2.3	542	517	85	77	43	42

Table 5 Concentration of the available fraction of eight nutrients in the pemba

Sample	Fe	Mg	Mn	Ca	Zn	Cu	Co	Ni
	(mg kg^−1)
Without reductant
Pr2	5.1	148	11	846	1.1	0.7	0.9	0.1
Pr3	7.2	275	27	106	2.0	4.3	5.3	1.0
Pr4	7.1	413	33	169	3.0	3.2	4.9	0.7
Pr5	7.2	260	20	283	2.7	2.7	2.8	0.5
Pw2	6.9	165	9	603	1.1	16.8	1.5	1.8
Pw3	5.3	142	3	338	1.5	1.6	1.2	2.6
Average (Pr)	6.7	274	23	351	2.2	2.7	3.5	0.6
Average (Pw)	6.1	153	6	471	1.3	9.2	1.4	2.2
Average (Total)	6.5	234	17	391	1.9	4.9	2.8	1.1
A/T (Pr)^†	0.00	8.4	2.8	76.9	3.0	3.5	7.0	2.2
A/T (Pw)^†	0.03	27.6	5.6	76.0	1.2	12.3	4.4	3.1
A/T (Total)^†	0.01	10.4	3.2	75.6	2.2	6.3	6.5	2.6
With reductant
Pr2	56.2	238	29	1294	1.4	0.9	2.8	0.0
Pr3	121.6	393	185	134	2.2	5.4	13.7	0.9
Pr4	72.5	551	103	209	3.5	3.7	10.9	0.4
Pr5	68.2	305	146	272	3.5	3.7	4.8	0.6
Pw2	34.2	195	30	581	0.9	15.4	3.7	2.0
Pw3	17.1	156	3	335	1.0	2.2	1.4	2.7
Average (Pr)	79.6	372	116	477	2.7	3.4	8.0	0.4
Average (Pw)	25.7	176	17	458	0.9	8.8	2.6	2.3
Average (Total)	61.6	306	83	471	2.1	5.2	6.2	1.1
A/T (Pr)^†	0.06	11.3	14.4	104.7	3.6	4.4	16.2	1.7
A/T (Pw)^†	0.14	31.6	15.6	73.9	0.9	11.7	8.2	3.3
A/T (Total)^†	0.07	13.6	15.2	91.0	2.4	6.7	14.6	2.5
^†Relative ratio of the available fraction to the total. Note: samples Pr1 and Pw1 could not be investigated because of their limited amounts.

Table 6 Relationship between the daily intake of available nutrients through pemba or corn flour and the daily requirement

	Fe	Mg	Mn	Ca	Zn	Cu	Co	Ni
	mg day^−1 (%)^‡‡
Intake-A (Pr)^†	0.33 (2)	13.7 (5)	1.1 (33)	17.5 (3)	0.11 (2)	0.14 (23)	0.17	0.03
Intake-B (Pr)^‡	3.98 (24)	18.6 (7)	5.8 (165)	23.9 (3)	0.13 (2)	0.17 (29)	0.40	0.02
Intake-A (Pw)^†	0.30 (2)	7.7 (3)	0.3 (8)	23.5 (3)	0.06 (1)	0.46 (77)	0.07	0.11
Intake-B (Pw)^‡	1.28 (8)	8.8 (3)	0.8 (24)	22.9 (3)	0.05 (1)	0.44 (73)	0.13	0.12
Intake-C (corn)^§	3.17 (19)	124 (48)	0.8 (22)	5.9 (1)	2.30 (38)	0.78 (130)	0.00	0.09
Daily requirement X^¶	16.5^§§	260^§§	3.5^¶¶	700^¶¶	6^§§	0.6^§§
Daily requirement Y^††	9.0^§§	230^§§	3.5^¶¶	700^¶¶	6^§§	0.5^§§
^†Intake (50 g day^−1) based on extraction without reductant.
^‡Intake (50 g day^−1) based on extraction with reductant.
^§Intake (300 g day^−1).
^¶Daily requirement by pregnant women.
^††Daily requirement by non-pregnant women.
^‡‡Relative percentage to the daily requirement by pregnant women (daily requirement A).
^§§Estimated average requirements.
^¶¶Adequate intake.

Figure 2  Relationship between the clay content and the cation exchange capacity (CEC) for the pemba (Pr; •), pemba (Pw; ▴) and the soil (□) samples.