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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