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Table 1 Recommended soil chemical test values for upland crops interpretation.

From: A chemical and multivariate statistical approach to assess the spatial variability of soil quality for environment around the Tamabil coal stockpile, Sylhet

Chemical parameters Very low Low Medium Optimum High Very high Critical limit
pH < 4.5 < 5.5 5.5–6 6.5 > 7.5 > 8 5
Total nitrogen (%) ≤ 0.09 0.091–0.18 0.181–0.27 0.271–0.36 0.361–0.45 > 0.45 0.12
OM < 1 1.0–1.7 1.8–2.6 2.7–3.4 3.5–5.5 > 5.5 1.2
P, (μg/g) ≤ 5.25 5.251–10.5 10.51–15.75 15.76–21.0 21.1–26.25 > 26.25 7.0
K, (meq/100 g) ≤ 0.09 0.091–0.18 0.181–0.27 0.271–0.36 0.361–0.45 > 0.45 0.12
S, (μg/g) ≤ 7.5 7.51–15.0 15.1–22.5 22.51–30.0 30.1–37.5 > 37.5 10.00
Fe, (μg/g) ≤ 3 3.1–6.0 6.1–9.0 9.1–12.0 12.1–15.0 > 15.0 4.00