Soil Fertility, Conservation and Management – Key Vocabulary

Vocabulary flashcards covering major terms, concepts, elements, processes, and practices related to soil fertility, plant nutrition, fertilizer management, soil erosion, and conservation measures. Designed for comprehensive exam preparation.

Early agronomist (1809) who proposed the humus theory, considering humus as the chief plant nutrient.

Albrecht Thaer

German chemist (1803-1873), father of agricultural chemistry; popularized the mineral theory and the Law of Minimum.

Justus von Liebig

Plant growth is limited by the nutrient present in the lowest relative amount, regardless of the abundance of other nutrients.

Law of Minimum

Soil’s capacity to supply essential nutrients in adequate amounts and proportions for plant growth.

Soil Fertility

Soil’s capability to produce plants under a specific management system; always requires fertility.

Soil Productivity

Supply and absorption of chemical elements or compounds required by plants for normal growth.

Plant Nutrition

Chemical elements or compounds required by plants and taken up mostly as ions in soil solution.

Nutrients (Plant)

Mechanisms converting elements to cellular materials or energy, driving biochemical reactions.

Metabolic Processes (Plants)

Element is essential if: plant can’t complete life cycle without it, function is irreplaceable, and it is directly involved in metabolism.

Essential Element Criteria (Arnon & Stout)

Element required in >100 mg kg⁻¹ (dry weight); includes C, H, O, N, P, K, Ca, Mg, S.

Macronutrient

Element required in <100 mg kg⁻¹; includes Zn, Cu, Fe, Mn, B, Cl, Mo, Ni.

Micronutrient

Element not essential to all plants but confers stress tolerance or other benefits; e.g., Na, Si, Co, Al, Se.

Beneficial Element

Major component of organic compounds in plants.

Carbon (C)

Major component of organic compounds; obtained from water.

Hydrogen (H)

Major component of organic compounds and cellular respiration.

Oxygen (O)

Component of amino acids, proteins, nucleic acids, chlorophyll; promotes vegetative growth and dark green color.

Nitrogen (N)

Component of DNA, RNA, ATP; vital for energy transfer, flowering, root development, and N fixation.

Phosphorus (P)

Enzyme activator; regulates osmotic pressure, stomatal movement, and enhances disease resistance.

Potassium (K)

Required for cell elongation, division, nitrate uptake; forms calcium pectate in cell walls.

Calcium (Ca)

Central atom in chlorophyll; part of ribosomes; involved in ATP-related energy transfer.

Magnesium (Mg)

Needed for sulfur-containing amino acids and vitamins; aids chlorophyll synthesis and flavor compounds.

Sulfur (S)

Participates in chlorophyll synthesis and electron-transfer enzymes.

Iron (Fe)

Catalyst in respiration; component of several enzymes.

Copper (Cu)

Cofactor in many enzymes regulating plant metabolism.

Zinc (Zn)

Controls oxidation-reduction systems; involved in O₂ evolution during photosynthesis.

Manganese (Mn)

Important in sugar translocation and carbohydrate metabolism.

Boron (B)

Component of nitrogenase and nitrate reductase; essential for N fixation.

Molybdenum (Mo)

Activates photosystem for O₂ production; involved in osmotic and ionic balance.

Chlorine (Cl)

Component of urease and hydrogenase; aids N compound mobilization.

Nickel (Ni)

Series of transformations: mineralization, nitrification, immobilization, denitrification, fixation, volatilization, plant uptake.

Nitrogen Cycle

Microbial conversion of organic N to ammonium (NH₄⁺).

Ammonification

Aerobic oxidation of NH₄⁺ to NO₃⁻ by bacteria; sensitive to pH, O₂, temperature.

Nitrification

Anaerobic reduction of NO₃⁻ to N₂, NO, N₂O gases, causing N loss.

Denitrification

Conversion of atmospheric N₂ to ammonium by symbiotic (Rhizobium) or free-living organisms.

Nitrogen Fixation

Loss of N as NH₃ gas, especially when ammonium fertilizers are surface-applied to high-pH soils.

Volatilization (N)

Nutrient supply mechanism where growing roots physically contact nutrient-bearing colloids (1–2 % soil volume).

Root Interception

Movement of nutrients to roots with transpiration water; main path for NO₃⁻ and Ca²⁺.

Mass Flow

Nutrient movement along concentration gradients toward roots; dominant for P, K, many cations.

Diffusion (Soil)

Model wherein metabolically energized carriers transport ions across root membranes (active uptake).

Carrier Theory

Non-selective ion entry via diffusion/ion exchange until Casparian strip; no metabolic energy required.

Passive Uptake

Energy-dependent, selective transport of ions against electrochemical gradients into root cells.

Active Uptake

Plant growth response showing rapid increase, diminishing returns, and plateau as nutrient supply rises.

Sigmoid Yield Curve

Zone where plants absorb nutrients above the level required for maximum yield without yield increase.

Luxury Consumption

Growth relationship: DY/DX = (A − Y) c; describes diminishing yield increments as input increases.

Mitscherlich’s Equation

15–40 °C optimal range; affects photosynthesis, respiration, water and nutrient absorption.

Growth Factor: Temperature

Water needed for photosynthesis and transport; deficits or excesses impair nutrient uptake.

Growth Factor: Moisture Supply

Drives photosynthesis; shading reduces growth unless species is shade tolerant.

Growth Factor: Solar Energy

Physical, chemical, biological attributes influencing nutrient availability and root growth.

Growth Factor: Soil Properties

Organic matter, soil minerals, adsorbed ions on colloids, and external additions (rainfall, fertilizers).

Sources of Soil Nutrients

Estimating native/residual nutrients and fertilizer needs for profitable crop production.

Soil Fertility Evaluation

Growing plants in soil (pot/field) to assess fertility through growth and yield comparisons.

Biological Test (Soil)

Observable plant disorder (chlorosis, necrosis, stunting) indicating lack of a specific nutrient.

Nutrient Deficiency Symptom

Laboratory determination of nutrient concentrations in plant samples to infer soil fertility.

Plant Tissue Analysis

Laboratory testing of soil samples for nutrient content, pH, CEC, salinity, etc.

Soil Analysis

N, P, K, Mg, Zn; deficiency symptoms appear in older leaves due to internal redistribution.

Mobile Elements in Plants

Ca, S, B, Fe, Cu, Mn; deficiencies show first in new growth.

Immobile Elements in Plants

Any material applied to soil or plants to supply essential nutrients.

Fertilizer (General)

Decomposed plant/animal material supplying nutrients; may be pure or fortified.

Organic Fertilizer

Mineral or synthetic product supplying nutrients, often as single or multi-nutrient formulations.

Inorganic (Chemical) Fertilizer

Supplies one primary nutrient, e.g., urea (46-0-0).

Single (Straight) Fertilizer

Contains two or three primary nutrients; e.g., ammonium phosphate.

Multinutrient Fertilizer

Provides all three primary nutrients N-P₂O₅-K₂O.

Complete Fertilizer

Guaranteed percentage analysis of N, P₂O₅, K₂O in the product.

Fertilizer Grade

Relative proportion of N:P₂O₅:K₂O in a fertilizer (e.g., 14-14-14 → 1:1:1).

Fertilizer Ratio

46 % N solid fertilizer; hygroscopic, fully soluble.

Urea

Gas fertilizer with 82 % N, injected under pressure into soil.

Anhydrous Ammonia

20-0-0 fertilizer containing ~24 % S; good for S-deficient soils.

Ammonium Sulfate

20 % P₂O₅ fertilizer, contains water-soluble P and minor nutrients.

Ordinary Superphosphate

Highly concentrated P fertilizer (monocalcium phosphate).

Triple Superphosphate

Potassium chloride (KCl); common K fertilizer, highly soluble.

Muriate of Potash

Even spreading of fertilizer on soil surface; common in closely spaced crops like rice.

Broadcast Application

Fertilizer placed in rows or bands near seeds or roots to increase efficiency.

Band Placement

Spraying nutrient solutions on leaves for quick correction, especially micronutrients.

Foliar Application

Applying dissolved fertilizers through irrigation water.

Fertigation

Addition of liming materials to raise acidic soil pH, enhancing nutrient availability and microbial activity.

Lime Application

Detachment and transport of soil particles by water, wind, or gravity to a new location.

Soil Erosion

Soil particle detachment caused by impact of falling raindrops on bare soil.

Splash (Raindrop) Erosion

Uniform removal of soil in a thin layer by surface runoff.

Sheet Erosion

Formation of small channels (rills) a few centimeters deep on slopes.

Rill Erosion

Advanced rill erosion creating large channels too big for normal tillage tools.

Gully Erosion

Erosion occurring along river or stream banks due to flowing water.

Streambank Erosion

Intrinsic susceptibility of soil to erosion, influenced by texture, structure, organic matter.

Soil Erodibility

Potential of rainfall to cause erosion, dependent on intensity and kinetic energy.

Rainfall Erosivity

A = 0.224 R K L S C P; predicts annual soil loss combining rainfall, soil, slope, cover, and practice factors.

Universal Soil Loss Equation (USLE)

Rainfall erosivity index reflecting intensity and kinetic energy of storms.

USLE R-factor

Soil erodibility factor measuring inherent soil susceptibility to erosion.

USLE K-factor

Cropping and management factor comparing soil loss under specific cover to bare soil.

USLE C-factor

Maximum erosion rate that allows sustainable, economical crop productivity.

Tolerable Soil Loss (T)

Mechanical conservation practice building level steps across slopes to slow runoff.

Terracing

Vegetated channel designed to convey runoff without causing erosion.

Grassed Waterway

Covering soil with residues to reduce splash, runoff, and conserve moisture.

Mulching (Conservation)

Planting dense grasses/legumes to protect soil, add organic matter, and suppress weeds.

Cover Cropping

Alternating erosion-permitting and conserving crops in strips along contours.

Strip Cropping

Growing crops in alleys between pruned rows of tree/shrub legumes for mulch and fertility.

Alley Cropping

Tillage systems leaving ≥30 % residue cover after planting to reduce erosion.

Conservation Tillage

Plowing and planting across slope lines to slow water flow and reduce erosion.

Contour Cultivation

Restricts soil disturbance to necessary operations, leaving interrow areas untilled.

Minimum Tillage

Deep ripping to break hardpan layers, improving infiltration and reducing runoff.

Subsoiling

Horizontal distance from the origin of overland flow to the point where runoff enters a defined channel; longer slopes increase erosion risk.

Slope Length

Uptake of nutrients beyond amounts needed for maximum growth without yield benefit.

Luxury Consumption (Nutrients)