Soil Fertility and Nutrient Management

1. Soil fertility = ability to supply essential nutrients to crops.
2. Soil productivity = capacity to produce crops under management.
3. Essential nutrients = 17 elements required for plant growth.
4. Macronutrients: N, P, K, Ca, Mg, S.
5. Micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl, Ni.
6. Liebig’s Law of Minimum — the scarcest nutrient limits yield.
7. Law of Diminishing Returns — beyond optimum, yield increase is small.
8. Nutrient mobility determines where deficiency symptoms appear.
9. Nitrogen promotes leaf growth and protein synthesis.
10. Phosphorus supports root growth and energy transfer (ATP).
11. Potassium improves water regulation and disease resistance.
12. Sulphur aids in amino acid and chlorophyll synthesis.
13. Calcium strengthens cell walls and root tips.
14. Magnesium is part of chlorophyll molecule.
15. Iron, manganese, and zinc are essential enzyme activators.
16. Boron aids sugar transport and flowering.

Problem Soils

1. Acid Soils

1. Acid soils have pH < 6.5.
2. High rainfall and leaching increase soil acidity.
3. Exchangeable Al³⁺ and H⁺ cause toxicity in acidic soils.
4. Lime (CaCO₃) neutralizes acidity and improves fertility.
5. Dolomite (CaMg(CO₃)₂) corrects both acidity and Mg deficiency.
6. Gypsum does not correct acid soils; it’s for sodic soils.
7. Acid soils reduce availability of P, Mo, and N.

2. Alkaline and Sodic Soils

1. Alkaline soils have high pH (> 8.5) and low soluble salts.
2. Sodic soils have ESP > 15% and high exchangeable sodium.
3. Sodium causes soil dispersion and poor structure.
4. Gypsum (CaSO₄·2H₂O) replaces Na⁺ with Ca²⁺ in sodic soils.
5. Leaching with good-quality water removes excess salts.
6. Sulfur application helps oxidize sodium in sodic soils.
7. Sodic soils reduce water infiltration and root growth.

3. Saline Soils

1. Saline soils have EC > 4 dS/m, pH < 8.5.
2. Excess soluble salts reduce osmotic potential, causing plant stress.
3. Leaching with adequate drainage removes salts.
4. Salinity is common in arid and semi-arid regions.
5. Crop tolerance to salinity varies; halophytes survive better.
6. Mulching and improved irrigation reduce salt accumulation.

4. Waterlogged Soils

1. Poor drainage leads to waterlogging and anaerobic conditions.
2. Waterlogging causes root suffocation and reduced microbial activity.
3. Raised beds, proper drainage, and aeration help reclaim waterlogged soils.
4. Anaerobic conditions favor formation of reduced Fe and Mn compounds.

5. Problem Soil Management Summary

1. Leaching + gypsum = sodic soil reclamation.
2. Lime = acidic soil correction.
3. Drainage + crop selection = waterlogged soil management.
4. Salt-tolerant crops improve productivity in saline soils.
5. Mulching, organic matter, and irrigation management prevent secondary salinization.

Remediation Techniques

1. Bioremediation – using microbes to degrade pollutants.
2. Phytoremediation – using plants to absorb or stabilize contaminants.
3. Soil washing – physical removal of pollutants.
4. Organic amendments improve microbial degradation of pollutants.
5. Proper waste management prevents further soil contamination.