Soil fertility

**Soil Horizons and Fertility Properties:**
– Soil horizons: O, A, B, C, E, R
– Major horizons in most soils: A, B, C
– Organic horizon: O, can be buried
– Eluviation in subsurface horizons: E
– Properties contributing to soil fertility: sufficient depth, good drainage, organic topsoil, optimal pH, adequate nutrients, presence of microorganisms

**Soil Fertilization and Nutrient Cycling:**
– Bioavailable elements: phosphorus, nitrogen, potassium
– Commercial fertilizer analysis: nitrogen, phosphorus, potassium
– Inorganic fertilizers: cost-effective
– Slow-release fertilizers: reduce leaching
– Constant cycling of nutrients between organic and inorganic forms

**Soil Conditioners, Depletion, and Challenges:**
– Peak phosphorus concern
– Materials improving soil quality
– Food waste compost vs. manure
– Soil depletion leading to poor yields
– Rapid land-use changes affecting fertility

**Light, CO2 Limitations, and Soil Impact:**
– Photosynthesis requirements: light, CO2
– Increasing CO2 benefits plant growth
– Soil depletion impact on plant life and production
– Challenges from droughts and soil degradation in certain regions

**Irrigation Effects and Global Distribution:**
– Quality of irrigation water crucial
– Effects of high alkaline, low pH, high salinity water on soil fertility
– Alkali soils prone to erosion
– Global distribution of soil types using USDA taxonomy system
– Mollisols in major grain-producing areas like North American Prairie States, Pampa, Gran Chaco, Ukraine-to-Central Asia Black Earth belt.