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.