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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, (ÎĽg/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, (ÎĽg/g)

≤ 7.5

7.51–15.0

15.1–22.5

22.51–30.0

30.1–37.5

> 37.5

10.00

Fe, (ÎĽg/g)

≤ 3

3.1–6.0

6.1–9.0

9.1–12.0

12.1–15.0

> 15.0

4.00