Chapter 37

Chapter 37: Plant Nutrition

Importance of Minerals

• Plants require minerals from the soil for growth and development.

• Key minerals include Nitrogen, Phosphorus, Potassium (N-P-K), and others.

  • Nitrogen: Essential for the synthesis of:

    • DNA and RNA

    • Proteins

    • Chlorophyll

  • Phosphorus: Critical for:

    • DNA and RNA

    • ATP synthesis in mitochondria

    • Phospholipids in cell membranes

  • Potassium: A cofactor for enzymes, important for turgor maintenance.

Soil Ecosystem

• Soil is a complex ecosystem housing various organisms.

• Plants largely depend on the upper soil layers for water and minerals.

• Soil properties:

  • Texture: Affected by rock breakdown. Sizes range from sand (0.02-2 mm) to clay (<0.002 mm).

  • Composition: Mixture of minerals, organic materials, and living organisms affecting plant life.

Soil Horizons

• Soil is layered into different horizons:

  • A Horizon (Topsoil): Rich in minerals, organisms, and humus.

  • B Horizon: Contains less organic material.

  • C Horizon: Comprises partially weathered rock.

Soil and Plant Growth

• Topsoil is crucial for plant growth; loams are ideal due to balanced texture of sand, silt, and clay.

• Sandy soils drain too quickly; clay soils retain excess water, limiting air for roots.

• Soil amendments (e.g., peat moss, compost) can enhance soil properties.

Soil Composition

• Topsoil made of inorganic and organic components.

• Inorganic Components:

  • Negatively charged particles (anions) dominate in healthy soils, but many essential nutrients are anions that do not bind to soil.

  • Cations (K+, Ca2+, Mg2+) adhere to soil particles and are important for plant nutrition.

Cation Exchange

• During cation exchange:

  • Cations displaced from soil particles can be taken up by plant roots.

  • Soil with more clay and organic matter has greater cation exchange capacity.

Organic Components

• Humus improves soil structure, retention of water, and enhances nutrient availability by interacting with other soil components.

Soil Life

• Diversity of Organisms: Includes bacteria, fungi, earthworms, insects, and more; they affect soil properties and fertility.

• For example, earthworms improve soil aeration and retention of moisture through their activity.

Agriculture and Soil Management

• Continuous cropping depletes soil nutrients; Fertilization can mitigate this.

• Overuse of agricultural land leads to nutrient depletion and erosion (e.g., the Dust Bowl). 30% of global farmland has reduced productivity due to mismanagement.

Sustainable Agriculture Practices

• Emphasis on conservation-minded, environmentally safe methods is crucial.

• Irrigation: Major water consumer, particularly in arid regions; leads to issues such as salinization.

• Effective use of drip irrigation minimizes water waste and salinization.

Fertilizers

• Commercial fertilizers supply essential nutrients (N-P-K) quickly but may not be retained in soil long-term.

• Organic fertilizers release nutrients gradually and improve soil quality.

Soil pH

• Influences nutrient availability; cations are more available in slightly acidic conditions due to H+ ions displacing other cations.

• Toxic elements like aluminum can increase in acidic soils, harming plant growth.

Erosion Control

• Preventing soil erosion through techniques such as planting trees as windbreaks, terracing, and contour farming.

Phytoremediation

• Plants can clean contaminated soils by accumulating pollutants in their tissues, supporting ecological restoration.

Essential Elements for Plants

• Of over 50 elements in plants, 17 are essential for completion of life cycle.

• They include macronutrients (e.g., nitrogen, phosphorus) and micronutrients (e.g., iron, zinc).

Nutrient Deficiencies

• Deficiencies manifest in poor growth or specific symptoms based on mineral role in the plant.

• Mobile nutrients typically affect older parts; less mobile affect younger parts more.

Global Climate Change and Nutrition

• Rising CO2 may enhance food production in specific areas, yet nutritional quality declines in some crops due to inadequate nutrient uptake.

Mutualistic Relationships

• Plants engage in mutualistic relationships with soil fungi and bacteria, enhancing nutrient uptake and growth.

  • Mycorrhizae: Fungi associated with roots that increase water and nutrient absorption.

• Nitrogen-fixing bacteria in legumes provide essential nitrogen through symbiotic relationships.

Fungi and Mycorrhizal Associations

• Mycorrhizae are crucial for plant nutrient uptake; these partnerships evolved to help early land plants thrive in nutrient-poor soils.

Unusual Nutritional Adaptations

• Epiphytes: Obtain water/minerals from rain without damaging the host.

• Parasitic plants: Extract nutrients from host plants.

• Carnivorous plants: Capture and digest insects for nitrogen.