7.3 Fertilizers and soil amendments

Fertilizers are crucial for boosting crop yields and soil health. From inorganic to organic, simple to compound, they come in various forms to meet specific plant needs. Understanding types and calculating application rates are key skills for effective nutrient management.

Applying fertilizers correctly is just as important as choosing the right type. Methods like broadcasting and banding have pros and cons. Soil amendments complement fertilizers by improving soil properties, enhancing overall fertility and plant growth.

Types and Calculations of Fertilizers

Types of fertilizers

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• Inorganic fertilizers synthesized through chemical processes boost crop yields rapidly (ammonium nitrate, urea, superphosphate)
• Organic fertilizers derived from plant or animal sources improve soil structure and microbial activity (compost, manure, bone meal)
• Simple fertilizers contain a single primary nutrient N, P, or K enhancing targeted plant nutrition
• Compound fertilizers contain two or more primary nutrients addressing multiple plant needs simultaneously
• Complete fertilizers contain all three primary nutrients N, P, K providing balanced plant nutrition
• Slow-release fertilizers gradually release nutrients over time reducing nutrient loss and improving efficiency
• Liquid fertilizers applied in solution form allow for quick absorption and precise application
• Granular fertilizers applied as solid particles offer ease of handling and storage

Fertilizer application rates

• Determine crop nutrient requirements based on expected yield and crop type (corn, wheat, soybeans)
• Interpret soil test results to assess nutrient levels present in the soil (pH, organic matter, macronutrients)
• Calculate nutrient deficiency by subtracting soil nutrient content from crop requirement
• Convert nutrient requirement to fertilizer amount using fertilizer grade (N-P-K ratio)
• Adjust for fertilizer efficiency accounting for nutrient losses and availability (leaching, volatilization)
• Calculate application rate by dividing fertilizer amount by area
• Formula for fertilizer application rate: $Rate (lbs/acre) = (Nutrient needed (lbs/acre) × 100) ÷ (Fertilizer grade percentage)$

Application Methods and Soil Amendments

Methods of fertilizer application

• Broadcasting spreads fertilizer uniformly over soil surface quickly but may lead to nutrient loss
• Banding places fertilizer in concentrated strips near plant roots reducing fixation but requires specialized equipment
• Foliar application sprays nutrients directly on leaves for rapid uptake but limited amounts can be applied
• Fertigation applies fertilizer through irrigation systems allowing precise application but may cause clogging
• Side-dressing applies fertilizer near growing plants reducing early-season losses but weather-dependent

Soil amendments for fertility

• Soil amendments improve physical or chemical properties of soil enhancing overall fertility
• Organic amendments (compost, peat moss, biochar) increase organic matter content and improve soil structure
• Inorganic amendments (lime, gypsum, sand) adjust pH and improve soil texture
• Soil amendments adjust pH, improve soil structure, enhance water retention, and increase nutrient availability
• Benefits include improved root growth, enhanced microbial activity, and increased cation exchange capacity (CEC)
• Consider soil type, existing conditions, and crop requirements when selecting amendments
• Apply amendments by incorporating into topsoil, top-dressing, or mixing with other soil media