Nutrient Cycling

Soil Science

Nutrient Cycling

  • Importance of soil in ecosystems

  • Role of soil in nutrient cycling is crucial for plant growth and agriculture

Functions of Soil

  • Medium for Plant Growth

    • Physical support

    • Aeration

    • Moisture supply and storage

    • Moderation of root-zone temperature

    • Moderation of phytotoxins

    • Provides 14 of the 17 essential nutrients

Essential Elements for Plant Growth

Macronutrients (>0.1% dry weight)

  • Calcium (Ca2+)

  • Magnesium (Mg2+)

  • Potassium (K+)

  • Nitrogen (NH4+ and NO3-)

  • Sulphur (SO4^2-)

  • Phosphorus (H2PO4-, HPO4^2-)

Micronutrients (<0.1% dry weight)

  • Copper (Cu2+)

  • Iron (Fe2+)

  • Manganese (Mn2+)

  • Nickel (Ni2+)

  • Zinc (Zn2+)

  • Boron (H3BO3-; H4BO4-)

  • Chlorine (Cl-)

  • Molybdenum (MoO4^2-)

Basic Macronutrients (90-95% of dry weight)

  • Carbon (CO2)

  • Hydrogen (H2O)

  • Oxygen (O2, H2O)

Nutrient Function Examples

  • Nitrogen (N): Amino acids, nucleic acids, chlorophyll

  • Phosphorus (P): Photosynthesis; ATP; cell walls

  • Potassium (K): Water regulation, chemical transport

  • Calcium (Ca): Cell walls

  • Magnesium (Mg): Chlorophyll; nucleic acids

  • Sulphur (S): Amino acids; chlorophyll

  • Important roles of micronutrients include enzyme activation and plant growth.

Soil Nutrient Availability

Soil Components

  • Soil Solution: Readily available nutrients and stored nutrients

  • Soil Organic Matter: Involved in nutrient storage and availability

  • Soil Minerals: Involved in nutrient exchange and cycling

Mineralization and Immobilization

  • Processes affecting nutrient availability include weathering, cation/anion exchange, and leaching.

Soil Fertility

  • Definition: Soil's ability to hold and make nutrients available for plant growth

  • Native Fertility: Determined by parent material and organic matter content

  • Managed Fertility: Enhanced by fertilizers, pH adjustments, amendments, and cover crops

Nitrogen Cycle

  • Limiting nutrient in terrestrial ecosystems

  • Present in the atmosphere as inert gas (N2)

  • Major sources: microbial fixation, lightning, industrial fixation (Haber-Bosch process)

  • Fertilizer nitrogen forms: urea, ammonia

Environmental Concerns

  • Excess nitrogen may lead to eutrophication and groundwater contamination.

Phosphorus and Sulphur

Phosphorus

  • Essential for ATP, DNA, and cell membranes

  • Often limiting nutrient due to low bioavailability

Sulphur

  • Involved in amino acids and proteins

  • Symptoms of deficiency: chlorotic leaves

Micronutrient Management

  • Micronutrients are present in soil primarily as metallic cations, required in small amounts.

  • Chelating agents increase their availability and prevent nutrient loss via leaching.

Conclusion

  • The relationship between soil science, agriculture, and environmental management is critical for sustainable agriculture.

  • Effective nutrient management is essential to optimize plant health and minimize environmental impacts.