Give account of soil fertility evaluation techniques. Enlist the points to be considered along with soil test values for fertiliser dose recommendation.

Soil Fertility Evaluation Techniques

Soil fertility evaluation involves assessing the availability of essential plant nutrients and other factors influencing plant growth. Techniques can be broadly categorized into physical, chemical, and biological methods.

Physical Methods

• Soil Texture Determination: Affects water holding capacity, aeration, and nutrient availability. Methods include feel method, ribbon method, and hydrometer method.
• Soil Colour: Can indicate organic matter content (darker soil generally indicates higher organic matter) and drainage conditions.
• Bulk Density & Water Holding Capacity: These parameters influence root growth and water availability.

Chemical Methods (Soil Testing)

Chemical methods, particularly soil testing, are the most widely used and reliable. They involve laboratory analysis to determine the levels of plant nutrients.

• pH Measurement: Indicates acidity or alkalinity, which affects nutrient availability.
• Electrical Conductivity (EC): Indicates the concentration of soluble salts. High EC can inhibit plant growth.
• Nutrient Analysis: Determines the levels of macronutrients (N, P, K) and micronutrients (Fe, Mn, Zn, Cu, B, Mo). Common methods include:
• Nitrogen: Kjeldahl's method, Dumas method.
• Phosphorus: Olsen's method, Double 418 method.
• Potassium: Flame Photometry, Atomic Absorption Spectrophotometry.
• Organic Carbon: Walkley-Black method, Loss on Ignition (LOI).

Biological Methods

• Microbial Biomass: Indicates the activity of soil microorganisms, which play a crucial role in nutrient cycling.
• Enzyme Activity: Measures the activity of enzymes involved in nutrient transformations (e.g., phosphatase for phosphorus mineralization).
• Earthworm Count: Earthworms improve soil structure and nutrient availability.

Points to Consider for Fertilizer Dose Recommendation

Fertilizer recommendations are not solely based on soil test values. A holistic approach is crucial.

• Crop Requirement: Different crops have different nutrient requirements.
• Soil Test Values: These are the primary basis for recommendations.
• Yield Target: Higher yield targets require higher nutrient inputs.
• Soil pH: Affects nutrient availability; adjustments may be needed.
• Organic Matter Content: High organic matter reduces the need for synthetic fertilizers.
• Previous Cropping History: Residual nutrients from previous crops need to be considered.
• Farmer's Economic Status: Recommendations should be economically feasible for the farmer.

Soil Test Values & Fertilizer Recommendations (Illustrative)

Nutrient	Low (ppm)	Medium (ppm)	High (ppm)	Recommendation (N-P-K kg/ha) – Illustrative
Available Nitrogen (kg/ha)	< 250	250-500	> 500	120-160-40
Available Phosphorus (ppm)	< 15	15-30	> 30	80-40-0
Available Potassium (ppm)	< 100	100-200	> 200	0-40-80

Note: These are indicative values and recommendations vary based on crop, region, and soil type. Consult local agricultural extension services for specific recommendations.

The Soil Health Card Scheme (SHC)

Launched in 2015, the SHC scheme aims to provide farmers with soil health cards containing information on the nutrient status of their soil and recommendations for fertilizer application. This promotes balanced fertilization and reduces input costs.

Case Study: SHC Implementation in Maharashtra – The Maharashtra government has actively promoted SHC distribution and awareness campaigns. Farmers have reported increased yields and reduced fertilizer costs after adopting the recommended practices. However, challenges remain in ensuring timely soil testing and providing adequate training to extension workers. Q: Why is soil pH important for nutrient availability? A: Soil pH affects the solubility and availability of nutrients. For example, phosphorus availability is optimal in a slightly acidic to neutral pH range (6.0-7.0). Extreme pH values can lock up nutrients, making them unavailable to plants. Nutrient Availability: The fraction of total nutrient in the soil that is in a form accessible to plants for uptake. It is influenced by soil pH, organic matter content, and microbial activity. According to the Indian Council of Agricultural Research (ICAR), approximately 30-40% of agricultural produce is lost due to nutrient deficiencies in soils. (Based on knowledge cutoff – 2023) Pradhan Mantri Kisan Sampada Yojana (PMKSY): This scheme includes components that support soil testing and promote balanced fertilization, contributing to improved soil health and farmer income. Soil Health: The soil's capacity to sustain plant and animal life, including its physical, chemical, and biological properties. The average organic carbon content in Indian soils is around 0.5%, which is significantly lower than the global average of 1.5% (Based on knowledge cutoff – 2023). Integrated Nutrient Management (INM): Combining organic manures (compost, vermicompost), biofertilizers, and chemical fertilizers in a balanced manner to improve soil health and nutrient use efficiency.