Agronomy: Soil Composition and Properties

• Agronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation
• It encompasses plant genetics, physiology, meteorology, and soil science

Soil Composition

• Soil comprises mineral matter, organic matter, water, and air
• Mineral matter is derived from rock weathering and varies in size (sand, silt, clay)
• Organic matter consists of decomposed plant and animal residues, improving soil structure, fertility, and water-holding capacity
• Water in the soil dissolves nutrients for plant uptake, while air provides oxygen for root respiration

Soil Properties

• Soil texture refers to the proportion of sand, silt, and clay, influencing water retention, drainage, and aeration
• Soil structure describes the arrangement of soil particles into aggregates, affecting water infiltration, root penetration, and erosion
• Soil pH measures acidity or alkalinity, impacting nutrient availability; most plants prefer a slightly acidic to neutral pH (6.0-7.0)
• Cation exchange capacity (CEC) is the soil's ability to hold positively charged nutrients (e.g., calcium, potassium), preventing leaching

Soil Fertility

• Essential plant nutrients include macronutrients (nitrogen, phosphorus, potassium) and micronutrients (iron, manganese, zinc)
• Nitrogen is vital for leaf and stem growth
• Phosphorus is essential for root development
• Potassium is important for disease resistance
• Nutrient deficiencies can cause stunted growth, chlorosis (yellowing), or necrosis (tissue death)

Soil Management Practices

• Tillage prepares the soil for planting, controls weeds, and incorporates crop residues; conservation tillage minimizes soil disturbance
• Crop rotation involves planting different crops in sequence to improve soil health, reduce pests, and balance nutrient use
• Cover cropping uses plants grown primarily to protect the soil from erosion, suppress weeds, and improve soil fertility
• Irrigation provides water to crops in dry conditions, increasing yields
• Drainage removes excess water from waterlogged soils, improving aeration
• Fertilization supplies essential nutrients to plants, either through synthetic fertilizers or organic amendments (compost, manure)
• Liming raises soil pH in acidic soils, improving nutrient availability and plant growth

Soil Erosion

• Soil erosion is the detachment and movement of soil by wind or water, degrading soil quality and polluting water resources
• Water erosion includes sheet erosion (uniform removal), rill erosion (small channels), and gully erosion (large channels)
• Wind erosion is common in dry areas with sparse vegetation
• Erosion control practices include terracing, contour plowing, strip cropping, and windbreaks

Soil Conservation

• Conservation tillage reduces erosion by leaving crop residues on the soil surface
• Cover crops protect the soil from erosion during fallow periods
• Terraces slow water flow and reduce erosion on sloping land
• Windbreaks reduce wind speed and erosion in windy areas
• Proper grazing management prevents overgrazing and soil degradation

Soil Health

• Soil health is the soil's capacity to function as a living ecosystem that sustains plants, animals, and humans
• Healthy soils have good structure, drainage, and nutrient availability
• They support a diverse community of soil organisms
• Soil health can be improved through practices like no-till farming, cover cropping, and organic amendments
• Soil testing assesses fertility and guides nutrient management decisions