Soil and Plant Nutrition

A collection of vocabulary flashcards covering soil composition, plant nutrition, essential elements, and symbiotic relationships from Concept 37.1 to 37.3.

Sand

Coarse soil particles ranging from $0.02-2\,mm$ in diameter.

Silt

Soil particles ranging from $0.002-0.02\,mm$ in diameter.

Clay

Microscopic soil particles less than $0.002\,mm$ in diameter.

Humus

The remains of dead organisms and other organic matter that, along with mineral particles released by weathering, forms topsoil.

Soil Horizons

The layers of soil, including the A horizon (topsoil), B horizon (less organic matter), and C horizon (partially broken-down rock).

Loams

The most fertile topsoils, composed of roughly equal amounts of sand, silt, and clay.

Soil Solution

The water and dissolved minerals in the pores between soil particles that nourish plants.

Cation Exchange

A process in which mineral cations are displaced from soil particles by other cations, particularly $H^+$, making them available for root absorption.

Leaching

The loss of nutrients from soil due to the percolation of water, which primarily affects negatively charged anions like $NO_3^-$, $H_2PO_4^-$, and $SO_4^{2-}$.

Sustainable Agriculture

A commitment to farming practices that are conservation-minded, environmentally safe, and profitable.

Aquifers

Underground water reserves that serve as a primary source of irrigation water.

Land Subsidence

The gradual settling or sudden sinking of the ground surface, often caused by the depletion of aquifers.

Soil Salinization

The accumulation of salts in the soil as water evaporates, which reduces the water potential of soil solution and diminishes water uptake by roots.

Drip Irrigation

A technology involving the slow release of water from perforated plastic tubing placed directly at the root zone to reduce water waste and salinization.

N-P-K Ratio

A three-number code on fertilizers (e.g., 15-10-5) representing the percentage of nitrogen, phosphorus, and potassium.

No-till Agriculture

A plowing technique that uses a special plow to create narrow furrows for seeds and fertilizer, minimizing soil disturbance and erosion.

Phytoremediation

A nondestructive biotechnology that uses plants to extract soil pollutants and concentrate them in harvestable portions for safe disposal.

Essential Element

A chemical element required for a plant to complete its life cycle and reproduce.

Hydroponic Culture

A research method where plants are grown in mineral solutions instead of soil to identify essential elements.

Macronutrients

The nine essential elements required by plants in relatively large amounts: carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium.

Micronutrients

Essential elements needed by plants in tiny quantities, mainly acting as enzyme cofactors: chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum.

Chlorosis

The yellowing of leaves, often a symptom of magnesium or iron deficiency.

Rhizobacteria

Bacteria that live in close association with plant roots or in the rhizosphere.

Rhizosphere

The soil layer closely surrounding plant roots.

Endophytes

Rhizobacteria that live between cells within the plant.

Nitrogen Cycle

The series of natural processes by which nitrogen-containing substances from air and soil are made available to living things and returned to the environment.

Nitrification

A two-step process in which nitrifying bacteria oxidize ammonia ($NH_3$) to nitrite ($NO_2^-$) and then to nitrate ($NO_3^-$).

Nitrogen Fixation

The multistep conversion of atmospheric $N_2$ to $NH_3$, summarized by the equation $N_2 + 8e^- + 8H^+ + 16\,ATP \rightarrow 2NH_3 + H_2 + 16\,ADP + 16\,P_i$.

Nodules

Swellings along legume roots composed of plant cells containing nitrogen-fixing Rhizobium bacteria.

Bacteroids

The form Rhizobium bacteria assume inside root nodules, where they are contained within vesicles.

Leghemoglobin

An iron-containing protein in root nodules that binds reversibly to oxygen, providing an anaerobic environment for nitrogenase.

Mycorrhizae

Mutualistic associations of roots and fungi where the fungus increases surface area for nutrient uptake and the plant provides sugar.

Ectomycorrhizae

A type of mycorrhiza where fungal hyphae form a mantle over the root surface and grow into the apoplast of the root cortex without penetrating cells.

Arbuscular Mycorrhizae

A type of mycorrhiza where hyphae penetrate root cell walls and form branching structures called arbuscules within the cortex.

Epiphyte

A plant that grows on another plant but gathers its own nutrients from rain and air, such as staghorn ferns or orchids.

Haustoria

Nutrient-absorbing projections used by parasitic plants to tap into the vascular tissue of a host plant.

Carnivorous Plants

Photosynthetic plants that supplement their mineral diet, particularly nitrogen, by capturing and digesting insects and small animals.