Agricultural Soil Science
1.Classification of Soil Particle Size
| Classification | Diameter (mm) (AgriExam.Com) | |
| IISS | USDA | |
| Gravel | >2.0 | >2.0 |
| Coarse Sand | 0.2 – 2.0 | 0.5 – 1.0 |
| Fine Sand | 0.02 – 0.2 | 0.1 – 0.25 |
| Silt | 0.002 – 0.02 | 0.002 – 0.05 |
| Clay | <0.002 | <0.002 |
2.Soil Classification Based on pH
| Soil type (AgriExam.Com) | pH range |
| Extremely acidic | <4.5 |
| Moderately acidic | 4.5-5.5 |
| Slightly acidic | 5.5-6.5 |
| Neutral | 6.5-7.5 |
| Slightly alkaline | 7.5-8.5 |
| Moderately alkaline | 8.5-9.5 |
| Extremely alkaline | >9.5 |
Agricultural Soil Science Important Points
3.Density of Different Soil
| Soil | Particle density (cm/cc) | Bulk density (cm/cc) |
| Normal Soil | 2.65 | 1-1.6 |
| Sandy Soil | 2.6 | 1.6 |
| Silty Soil | 2.7 | 1.3 |
| Clay Soil | 2.8 | 1.1 |
4.Total pore space of soil
AgriExam.com
| Soil | Pore space |
| Sandy | 20-30% |
| Loamy | 30-50% |
| Clay | 50-60% |
5.Specific heat
| Material | Specific heat (Cal./gm) |
| Water | 1 |
| Organic matter | 0.462 |
| Clay soil | 0.22 |
| Air | 24 |
| Humus | 0.4 |
| Ice | 0.5 |
6.Heat Capacity
| Material | Heat Capacity (Cal./cm3) |
| Organic matter | 0.60 |
| Water | 1 |
| Air | 0.003 |
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7.Cation Exchange Capacity (CEC) of Soils
| Soil texture | CEC (meq/100 gm) |
| Sand (light colour) | 3-5 |
| Sand (dark colour) | 10-20 |
| Loam | 10-15 |
| Silt loam | 15-25 |
| Clay and clay loam | 20-50 |
| Organic soil | 50-100 |
8.Conversion factors
| Conversion factors (AgriExam.Com) | |
| N | No3 x 0.22 |
| No3 | N x 4.54 |
| P | P2O5 x 0.44 |
| P2O5 | P x 2.27 |
| K | K2O x 0.83 |
| K2O | K x 1.20 |
| Ca | CaO x 0.71 |
| CaO | Ca x 1.40 |
| Mg | MgO x 0.61 |
| MgO | Mg x 1.63 |
| OM | OC x 1.724 |
| OC | OM x 0.58 |
OM= Organic matter
OC = Organic carbon
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9.Soil Test Rating Chart for Available Nutrients
| Nutrient | Low level | Medium level | High level |
| N | <250 kg/ha | 250-500 kg/ha | >500 kg/ha |
| P | <20 kg/ha | 20-50 kg/ha | >50 kg/ha |
| K | <125 kg/ha | 125-300 kg/ha | >300 kg/ha |
| Zn/Cu | <0.5 ppm | 0.5-1.0 ppm | >1.0 ppm |
| Mn | <1.0 ppm | 1.0-3.0 ppm | >3.0 ppm |
| B | <0.33 ppm | 0.33-0.67 ppm | >0.67 ppm |
| OC | <0.5% | 0.5-0.75% | >0.75% |
Agricultural Soil Science Important Points
10.Soil colour
It is found out by using Munsell Colour Chart. Three variable are used to denote soil colour.
| Component of Soil Colour (AgriExam.Com) | |
| HUE | Denotes the dominant spectral colour (Yellow, red blue, brown etc.) |
| VALUE | Denotes the lightness and darkness of colour |
| CHROMA | Denotes purity of colour |
11.Antagonistic Effect
| Excess of nutrient (AgriExam.Com) | Causes deficiency |
| Ca | P |
| Ca, Mg | K |
| K, NH4 | Mg |
| Fe, SO4 | Mo |
| P | Zn |
| N, P, K | Cu |
| NO3 | Fe |
| Zn, Al | Cu |
| N, K, Ca | B |
12.Different nutrient test method in soil
| Nutrient Determination | Analyzing Process |
| Total Nitrogen in soil | Kzeldahl Process |
| Available N | Alkaline Permanganate method |
| Phosphursus in acid condition | Bray No.1 |
| Phosphursus in neutral and alkaline condition | Olsen’s Method |
| K & Na | Flame photometer |
| Sulphate sulphure (SO4) | Terbimatric Method |
| Organic carbon | a)Walke & Black method b)Rapid Oxidation process (KMnO4) c)Morgan’s method |
| Available K (Potash) | Ammonium Acetate |
| Important Table – 1 | Cl;ick |
| Important Table – 2 | Cl;ick |
| One Liner | Cl;ick |
| Fertilizers classification | Cl;ick |
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