Soil Fertility, Productivity, Indicators & Soil Management

Soil Fertility

• Definition: Soil fertility is the inherent capacity of soil to supply essential plant nutrients in available form, in proper amount, and in balanced proportion for plant growth without producing toxic substances.

Types of Soil Fertility

• Natural fertility – inherent nutrient status of soil (undepleted condition).
• Acquired fertility – achieved through external inputs (fertilizers, manures, amendments).
• Apparent fertility – fertility reflected in crop performance under field conditions.

Factors Affecting Fertility

• Parent material
• Organic matter content
• Soil texture & structure
• pH, EC, CEC
• Microbial activity
• Cropping intensity & nutrient mining

Soil Productivity

• Definition: Soil productivity is the capacity of soil to produce a specific crop or sequence of crops under a specific management system.
• It is an economic concept (yield per unit area).

Relation between Fertility & Productivity

• All productive soils are fertile, but not all fertile soils are productive. Example: A fertile soil with good nutrients but waterlogged or saline may not be productive.
• Productivity depends not only on fertility but also on climate, management, crop variety, irrigation, etc.

Indicators of Soil Fertility & Productivity

Physical Indicators

• Texture: Sandy → low fertility; Clay loam → high fertility.
• Structure: Good aggregation improves aeration, water, and nutrient retention.
• Bulk Density (BD): Optimum = 1.2–1.4 g/cm³. Higher BD → compaction.
• Porosity & WHC (Water Holding Capacity): Higher WHC → better fertility.
• Colour: Dark colour → higher organic matter and fertility.

Chemical Indicators

• pH: Optimum 6.5–7.5.
  • Acid soils (<6) → Al, Fe, Mn toxicity.
  • Alkaline soils (>8.5) → CaCO₃, sodicity issues.
• Electrical Conductivity (EC): <4 dS/m → non-saline.
• CEC (Cation Exchange Capacity): Higher CEC = higher nutrient-holding capacity.
• Base Saturation: % of exchange sites occupied by Ca²⁺, Mg²⁺, K⁺, Na⁺. (>50% = good).
• Organic Carbon: >0.75% = high fertility.
• Available Nutrients: N, P, K, S, micronutrients.

Biological Indicators

• Soil microbial biomass C & N.
• Enzyme activity: Dehydrogenase, phosphatase → reflect microbial activity.
• Earthworm population: Natural indicator of soil health.
• Nitrogen-fixing and P-solubilizing microbes.

Features of Good Soil Management

A well-managed soil ensures sustained fertility, high productivity, and environmental safety.

Nutrient Management

• Balanced use of N, P, K + secondary + micronutrients.
• Integrated Nutrient Management (INM): combination of inorganic fertilizers, organic manures, biofertilizers.
• Avoid overuse of chemical fertilizers.

Organic Matter Maintenance

• Regular addition of FYM, compost, green manure, crop residues, biochar.
• Mulching to reduce evaporation & improve soil structure.

Soil pH & Salinity Management

• Acid soils: Apply lime.
• Saline soils: Improve drainage, apply gypsum, grow salt-tolerant crops.
• Sodic soils: Gypsum application + leaching.

Soil Moisture Management

• Irrigation scheduling according to crop stage.
• Rainwater harvesting, mulching, conservation tillage.
• Proper drainage to avoid waterlogging.

Erosion & Degradation Control

• Mechanical measures: Terracing, bunding, contour farming.
• Biological measures: Cover crops, agroforestry, grass strips.
• Avoid overgrazing, deforestation.

Soil Biological Health

• Encourage biofertilizers (Rhizobium, Azotobacter, PSB, mycorrhiza).
• Reduce dependence on chemical pesticides.
• Crop rotation & inclusion of legumes.

Sustainable Practices

• Conservation agriculture (minimum tillage, residue retention).
• Precision farming (site-specific nutrient management).
• Use of nano-fertilizers, fortified fertilizers.

5. Key Differences: Fertility vs Productivity

Exam Pointers 

• Fertility = nutrient supplying capacity; Productivity = yield producing capacity.
• Indicators: Physical (texture, BD), Chemical (pH, EC, CEC), Biological (microbial biomass, enzyme activity).
• Good soil management = balanced fertilization + organic matter + erosion control + moisture + biological activity.