SOIL FERTILITY CLASSES/CRITICAL LEVELS


SOIL REACTION (pH)

Soil pH was grouped as per the 11 classes and frequency distribution of soil pH classes worked out

SOIL pH CLASSES AND LIME RECOMMENDATION

Class Nomenclature pH range Lime recommendation (kg CaCO3 ha-1)
1 Ultra acid < 3.5 1000
2 Extremely acid 3.5 - 4.4 850
3 Very strongly acid 4.5 - 5.0 600
4 Strongly acid 5.1 - 5.5 350
5 Moderately acid 5.6 - 6.0 250
6 Slightly acid 6.1 - 6.5 100
7 Neutral 6.6 - 7.3 -
8 Slightly alkaline 7.4 - 7.8 -
9 Moderately alkaline 7.9 - 8.4 -
10 Strongly alkaline 8.5 - 9.0 -
11 Very strongly alkaline > 9.0 -

FREQUENCY DISTRIBUTION OF OC, AVAILABLE P AND K


Soil analysis data of organic carbon, available P and K were grouped as low, medium or high as per the soil fertility rating followed in the Soil Testing Laboratories under the Department of Agriculture. Based on the above rating, frequency distribution of OC, P and K and nutrient index worked out.

SOIL FERTILITY RATING FOR MAJOR NUTRIENTS


Soil parameters Low Medium High
Organic carbon (%) ≤ 0.7 > 0.7 - ≤1.5 > 1.5
Available phosphorus (kg ha-1) < 11 ≥ 11 - ≤24 > 24
Available potassium (kg ha-1) < 116 ≥ 116 - ≤ 275 > 275

Nutrient Index (Parker et al., 1951)
The concept of nutrient index has been used for area wise fertilizer recommendation and comparison of soil fertility levels of different panchayats. The nutrient index is calculated giving weightage to number of samples falling low (Nl), medium (Nm) and high (Nh) fertility classes as indicated below.


Nutrient index = (Nl x 1 + Nm x 2 + Nh x 3) ÷ Nt

Where, Nt = Total number of samples analyzed


Nutrient Index


Low Medium High
Less than 1.5 1.5 to 2.5 Greater than 2.5

FREQUENCY DISTRIBUTION OF SECONDARY NUTRIENTS


Soil analysis data of secondary nutrients (calcium, magnesium and sulphur) were grouped as adequate /deficient based on the critical levels and recommendations as suggested by the Kerala Agricultural University and frequency distribution worked out

CRITICAL LEVELS OF SECONDARY NUTRIENTS AND RECOMMENDATION


Nutrients Deficiency Adequate Recommendation
Calcium ≤ 300 mg kg-1 > 300 mg kg-1 As per lime requirement
Magnesium ≤ 120 mg kg-1 > 120 mg kg-1 MgSO4 @ 80 kg ha-1
Sulphur < 5 mg kg-1 ≥ 5 mg kg-1 Sulphur @ 25 kg ha-1

FREQUENCY DISTRIBUTION OF MICRO NUTRIENTS


Soil analysis data of micro nutrients (copper, zinc and boron) were grouped as adequate /deficient based on the critical levels and recommendations as suggested by the Kerala Agricultural University and frequency distribution worked out

CRITICAL LEVELS OF MICRO NUTRIENTS AND RECOMMENDATION


Nutrients Deficiency Adequate Recommendation
Copper* < 1.0 mg kg-1 ≥ 1.0 mg kg-1 CuSO4 @ 2 kg ha-1
Zinc* < 1.0 mg kg-1 ≥ 1.0 mg kg-1 ZnSO4 @ 20 kg ha-1 or foliar spray (0.5 %)
Boron** < 0.5 mg kg-1 ≥ 0.5 mg kg-1 Borax @ 10 kg ha-1 or foliar spray (0.5 %)

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