In-Depth Notes on Plant Nutrition

Plant nutrition encompasses:
- Absorption of raw materials vital for biochemical processes
- Distribution within the plant
- Utilization in metabolism and growth

Definition: Chemical elements crucial for normal plant growth and development.
Criteria for essentiality:
- Element must be necessary for the plant to complete its life cycle (e.g., produce viable seeds).
- Element must be part of larger compounds essential for the plant (e.g., $Mg$ in chlorophyll, $N$ in proteins).
- Deficiency symptoms must be evident when the element is absent.
At least 17 essential elements identified for plants.

Macronutrients: Required in large amounts (> 1000 mg/kg dry weight).
Micronutrients (trace elements): Required in trace amounts (< 100 mg/kg dry weight).
Most nutrients are absorbed as inorganic ions from the soil. Some non-essential and toxic elements can also be absorbed.

Macronutrients (from soil and water):
- Nitrogen ($N$): 1.5%
- Potassium ($K$): 1%
- Calcium ($Ca$): 0.5%
- Magnesium ($Mg$): 0.2%
- Phosphorus ($P$) and Sulfur ($S$): 0.1% each
Micronutrients:
- Iron ($Fe$): 100 ppm
- Boron ($B$): 20 ppm
- Manganese ($Mn$): 50 ppm
- Other critical micronutrients include Copper ($Cu$), Nickel ($Ni$), and Molybdenum ($Mo$).

Definition: Elements that are essential for specific plant groups or environmental conditions, often needed in small amounts; may be toxic in large amounts.
Examples:
- Aluminum: Beneficial in small amounts for plants like Camellia sinensis.
- Cobalt: Essential for legumes, aiding symbiotic bacteria.
- Silicon: Found in Equisetum spp., supports the plant and deters herbivores.
- Sulfur: Accumulates in mustard family plants for sharp-tasting mustard oils.

Knowledge of essential functions can help identify deficiencies.
Symptoms include:
- Necrosis: Localized cell death.
- Chlorosis: Yellowing of leaves due to chlorophyll loss.
Mobility impacts symptoms:
- Phloem-mobile nutrients (e.g., Mg, P, K, N) show symptoms in older leaves.
- Phloem-immobile nutrients (e.g., B, Fe) show symptoms in younger leaves.

Soil provides physical support, nutrients, and water.
Types of soil textures:
- Clay: Small particles with high water retention.
- Silt: Intermediate particle size.
- Sand: Coarse particles enhancing drainage.
Soil horizons include:
- A (topsoil): Rich in organic material, high biological activity.
- B (subsoil): Accumulation layer with less organic matter.
- C (parent material): Mainly composed of larger rocks and minerals.

Water availability for plants influenced by soil texture and structure:
- Field Capacity: Maximum water retained against gravity.
- Wilting Point: Water levels when plants can no longer absorb enough water.
Pore space influences water retention properties, varying between coarse and fine-textured soils.

Overview of nitrogen sources and transformations:
- Ammonification: Organic N decomposes to ammonia ($NH_4^+$).
- Nitrification: Ammonia oxidized to nitrate ($NO_3^-$), which is plant-available.
- Denitrification: Nitrate reduced to gaseous forms, escaping the soil.
Nitrogen fixation converts atmospheric nitrogen ($N2$) into a usable form ($NH4^+$) facilitated by nitrogen-fixing bacteria (e.g., Rhizobia).

Hyperaccumulators: Plants that accumulate higher concentrations of certain elements than found in soil.
Phytoremediation: Use of plants to clean contaminated soils; involved in absorption, stabilization, or degradation of pollutants.
Only a small percentage of species are considered hyperaccumulators, often belonging to specific plant families like Brassicaceae.

Understanding plant nutrition is critical for successful gardening, agriculture, and ecosystem management. This includes knowledge of essential and beneficial elements, their effects on plant health, soil properties, and interactions within the nitrogen cycle.