Assessing Soil Nutrients Variability and Adequacy for the Cultivation of Maize, Cassava, and Sorghum in Selected Agroecological Zones of Cameroon

Table 7

Critical values of nutrients and soil properties.

Soil chemical properties	Critical level
	Very low	Low	Medium	High	Very high	Reference
Organic matter (%)	0–0.3	0.4–1.2	1.3–2.2	2.3–3.2	3.3+	[44]
Estimated N release (lbs acre^−1)	0–26	27–37	38–47	48–57	58+	[44]
Total exchangeable cation (meq/100 g)	0–4	5–11	12–24	25–40	41+	[49]
P (mm kg^−1)	0–12	13–22	23–35	36–68	69+	[50]
Ca (mm kg^−1)	0–307	308–503	504–700	701–895	896+	[50]
Mg (mm kg^−1)	0–22	23–41	42–71	72–147	148+	[50]
K (mm kg^−1)	0–20	21–40	41–72	73–138	139+	[50]
S (mm kg^−1)	0–10	11–20	21–30	31–40	41+	[59]
B (mm kg^−1)	–	<0.70	0.71–1.00	>1.00	—	[60]
Fe (mm kg^−1)	–	<60	60–420	>420	—	[60]
Mn (mm kg^−1)	–	<30	30.1–200	>200	—	[60]
Cu (mm kg^−1)	–	<1.6	1.6–4.5	>4.5	—	[60]
Zn (mm kg^−1)	–	<2.2	2.21–5.0	>5.0	—	[60]