Legumes and the Nitrogen Cycle

Includes both herbs and trees.
Leaves:
- Usually pinnately or palmately compound.
- Some species have simple leaves.
Flowers:
- Typically consist of five petals.
- Display bilateral symmetry.
Fruits:
- The fruit type is a pod, commonly referred to as a legume.
- Contains a single row of seeds that are rich in oil and protein.
Seeds:
- Characterized by two prominent cotyledons.

Importance of Nitrogen:
- Nitrogen is an essential element for all organisms.
N₂ Fixation:
- Nitrogen gas (N₂) is non-usable by most organisms.
- Cyanobacteria play a key role in the fixation of N₂.
Components of the Nitrogen Cycle:
- NH₄⁺ (Ammonium): Produced from nitrogen fixation and decomposition processes.
- NO₂⁻ (Nitrite): Produced by nitrite-producing bacteria.
- NO₃⁻ (Nitrate): Formed through further oxidation of nitrites.
- Dead organisms and animal waste contribute to the nitrogen cycle by providing nitrogen in various forms.
- Denitrification occurs via specialized bacteria, converting nitrates back into nitrogen gas (N₂).

Key Pollutants:
- Volatile Organic Compounds (VOCs) and Nitrogen Oxides (NO₂).
- Ozone Formation:
- Ground-level ozone, considered harmful, forms from chemical reactions of NOx and VOCs in the presence of heat and sunlight.
Fertilizer Run-off:
- Leads to algal blooms in water bodies.
- NO₂ from fertilizers contributes to climate change.
Fossil Fuel Combustion:
- Emits nitrogen oxides (NOx) as pollutants.
Potential Solutions:
- Introduction of biofertilizers that include nitrogen-fixing bacteria.
- Utilizing genetic engineering for crops that enhance nitrogen-fixation in root microbiomes.

Beans:
- Oldest and most common legume types.
- Exhibit a variety of shapes, colors, and sizes.
- Protein content ranges from 17% to 31%, with an average of 25%.
- Beans are typically warm-season annuals requiring moderate rainfall.
Major Varieties:
- Adzuki Beans (Vigna angularis): Popular in Japan for desserts.
- Anasazi Beans (Phaseolus vulgaris): Heirloom variety notable for color.
- Black-eyed Peas (Vigna unguiculata): A traditional Southern dish.
- Lentils (Lens culinaris): An important crop in India, used in soups.
- Chickpeas (Cicer arietinum): Common in Mediterranean dishes.
- Kidney Beans (Phaseolus vulgaris): Frequently used in chili.
- Peas (Pisum sativum): Smaller, rounder than beans and suited for cooler climates.

Scientific Name: Arachis hypogea.
Origin: South America; recognized as a tetraploid from the hybridization of A. ipaensis and A. duranensis.
Adaptation: Best grown in warm climates and sandy soils.
Nutritional Value:
- Contains 26% protein, 16% carbohydrates, and 49% lipids; of which:
- 2% is saturated fats.
- 50% is monounsaturated.
- 32% is polyunsaturated.
Uses: Consumed raw, boiled, roasted; processed into peanut oil and peanut butter.
Cultural Significance: Introduced to Southern agriculture by George Washington Carver after the Civil War.

Scientific Name: Glycine max.
Historical Notes: One of the five sacred crops in China with domestication dating back at least 3,000 years.
Uses: Includes soy sauce, soy nuts, soy milk, tofu, edamame, miso, and tempeh.
Nutritional Content:
- Composed of 25% oil and between 30-50% protein; additionally includes lecithin and phytoestrogens.
Preparation Note: Cannot be eaten raw due to the presence of trypsin inhibitors; can serve as a meat substitute.

Plant Uses:
- Carob (Ceratonia siliqua): A chocolate substitute.
- Indigo (Indigofera tinctoria): Source of dye.
- Licorice (Glycyrrhiza glabra): Extract used for flavoring.
- Tamarind (Tamarindus indica): Used as a seasoning.
Unique Legumes:
- Jicama (Pachyrhizus erosus): Cultivated as a root crop, high in protein.
- Groundnut (Apios americana): Provides pods and tubers with a protein content of 12-13%.
- Winged Bean (Psophocarpus tetragonolobus): Edible parts with seeds containing 37% protein and 20% oil.
- Lead Tree (Leucaena spp.): A fast-growing tropical tree providing edible protein-rich seeds.
- Alfalfa (Medicago sativa): Oldest forage crop, essential for livestock feed.