Soil Fertility, Plant Nutrition, Fertilizers & Conservation

Vocabulary flashcards summarizing key terms and definitions from the lecture notes on soil fertility, plant nutrition, fertilizer management, and soil conservation.

C/N Ratio After Composting

Reduced to about 14–20:1 in mature compost.

Thermophilic Stage

50–75 °C phase in composting that destroys pathogenic organisms but not heavy metals.

Cellulose

One of the most abundant forms of organic matter in nature; decomposed by specific microbes.

Cellulose-Decomposing Fungi

Genera include Aspergillus, Chaetomium, Curvularia, Fusarium, Memnoniella, Phoma, Thielavia, Trichoderma.

Cellulose-Decomposing Bacteria

Genera include Bacillus, Cellulomonas, Clostridium, Corynebacterium, Cytophaga, Polyangium, Sporocytophaga, Vibrio.

Bacillus (Soil Context)

Aerobic, spore-forming, Gram-positive rods capable of digesting cellulose.

Cellulomonas

Short Gram-negative rods producing yellow water-insoluble pigments; digests cellulose.

Clostridium (Cellulolytic)

Anaerobic, non-motile, Gram-negative rods that digest cellulose and produce yellow pigment.

Cytophaga

Aerobic, long flexuous rods abundant in straw- or manure-amended soils; digest cellulose.

Soil Fertility

Soil’s capability to supply nutrients in the right amounts and proportions for crop needs.

Soil Productivity

Ability of soil to support or produce a desired quantity of yield; always implies fertility.

Plant Nutrition

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

Essential Element

Chemical element required for plants to complete their life cycle; cannot be substituted.

Macronutrient (Plant)

Essential element absorbed in large amounts (e.g., N, P, K, Ca, Mg, S).

Micronutrient (Plant)

Essential element required in trace amounts (e.g., Fe, Mn, Zn, Cu, B, Mo, Cl, Ni, Co).

Mobile Nutrient

Element whose deficiency symptoms appear first on older leaves (e.g., N, P, K, Mg, Zn).

Immobile Nutrient

Element whose deficiency symptoms appear first on younger leaves (e.g., Ca, S, Fe, Cu, Mn, B).

Metabolic Process (Plant)

Mechanism converting elements to cellular materials or energy sources.

Carbon (C)

Major component of plant organic compounds; taken as CO₂.

Hydrogen (H)

Major component of plant organics; supplied mainly from water.

Oxygen (O)

Major component of organics; absorbed as O₂ or H₂O.

Nitrogen (N) Function

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

Phosphorus (P) Function

Key in ATP/ADP energy transfer, nucleic acid structure, seed formation, early maturity, root growth.

Potassium (K) Function

Enzyme activator; regulates osmotic and turgor pressure; strengthens straw; enhances disease resistance.

Calcium (Ca) Function

Required for cell elongation, cell wall pectate formation, and regulates cation uptake.

Magnesium (Mg) Function

Central atom in chlorophyll; part of ribosomes; involved in energy transfer reactions.

Sulfur (S) Function

Needed for sulfur amino acids, coenzymes, chlorophyll synthesis, characteristic flavors of onion/mustard, oil formation.

Iron (Fe) Function

Involved in chlorophyll synthesis and electron-transfer enzymes.

Copper (Cu) Function

Catalyst in respiration; component of enzymes.

Zinc (Zn) Function

Part of enzyme systems regulating metabolic activities.

Manganese (Mn) Function

Controls oxidation-reduction systems; involved in O₂ formation in photosynthesis.

Boron (B) Function

Important in sugar translocation and carbohydrate metabolism.

Molybdenum (Mo) Function

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

Chlorine (Cl) Function

Activates system for O₂ production in photosynthesis.

Nickel (Ni) Function

Component of urease and hydrogenase; involved in N compound mobilization.

Cobalt (Co) Function

Essential for symbiotic nitrogen fixation in legumes.

Mass Flow

Movement of nutrients with water toward roots during uptake; major for Ca, Mg, Zn, Cu, B, Fe.

Diffusion (Soil Nutrients)

Movement of ions from high to low concentration; supplies mainly P and K to roots.

Contact Exchange (Interception)

Direct ion exchange between root surfaces and soil colloids when in contact.

Passive Uptake

Non-selective ion absorption by diffusion/ion exchange; requires no metabolic energy.

Active Uptake

Energy-requiring transport of ions against electrochemical gradient via carriers; selective.

Carrier Theory

Model where metabolically energized carriers transport ions from outer to inner root spaces.

Nitrate Uptake

Active absorption; increases at low pH; occurs against electrochemical gradient.

Ammonium Uptake

Optimal at neutral pH; decreases as pH drops; can be toxic as NH₃ gas.

Phosphorus Uptake

Active, pH-dependent with higher uptake at low pH; rapidly assimilated and translocated.

Potassium Uptake

Active high-rate uptake; only essential cation transported against electrochemical gradient; luxury consumption possible.

Calcium Uptake

Primarily passive; largely immobile once deposited; moves to shoot apex.

Magnesium Uptake

Competitive with NH₄⁺, K⁺, Ca²⁺, Mn²⁺; mobile in phloem; passive in transpiration stream.

Sulfur Uptake

Active absorption as SO₄²⁻; mainly upward translocation; foliage may absorb atmospheric H₂S.

Liebig’s Law of Minimum

Plant growth is limited by the nutrient in least supply relative to need.

Mitscherlich Equation

Describes diminishing yield increases as limiting nutrient is added; DY/DX = C(A−Y).

Sigmoid Growth Curve

Yield response curve showing rapid, then slowing, then leveling growth with increasing nutrient supply.

Luxury Consumption (Plants)

Nutrient uptake beyond that needed for maximum yield, without yield increase.

Growth Factors (Environmental)

Temperature, moisture, solar energy, and soil properties affecting plant growth.

Soil Analysis

Chemical extraction procedure estimating available nutrient supply in soils.

Soil Sampling

Process of collecting representative 0.5 kg soil sample; critical to accurate soil testing.

Shallow-Rooted Crop Sampling Depth

Surface 20–30 cm layer.

Deep-Rooted Crop Sampling Depth

Includes subsoil to match rooting depth.

Plant Tissue Analysis

Laboratory determination of nutrient content in plant tissues to assess soil fertility.

Fertilizer Field Trial

On-farm experiment assessing fertilizer effects under actual conditions.

Pot Experiment

Controlled comparison of fertilizer treatments in containers; preliminary and artificial.

Fertilizer (Definition)

Substance applied to soil or plants to supply essential nutrients.

Organic Fertilizer

Decomposed plant/animal product supplying nutrients; e.g., compost, manure.

Pure Organic Fertilizer

Organic fertilizer with no added chemicals to raise nutrient content.

Fortified Organic Fertilizer

Organic fertilizer enriched with inoculants, hormones, or chemical additives.

Inorganic Fertilizer

Mineral or synthetic fertilizer supplying nutrients as chemical compounds.

Single Nutrient (Straight) Fertilizer

Supplies one primary nutrient, e.g., urea, ammonium sulfate.

Multi-Nutrient Fertilizer

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

Complete Fertilizer

Supplies all three primary nutrients N-P-K.

Fertilizer Grade

Weight percent of N, P₂O₅, K₂O stated on label.

Fertilizer Ratio

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

Broadcast Application

Evenly spreading fertilizer over soil surface; typical for rice.

Band Placement

Applying fertilizer in a band below or beside seeds; common for corn and fruit trees.

Foliar Application

Spraying nutrients onto leaves for rapid correction, especially micronutrients.

Ring Application

Placing fertilizer in a circular band around a tree base.

Hole Application

Dropping fertilizer into holes around trees.

Spot Application

Small fertilizer amounts placed beside each plant or hill.

Basal Application

First fertilizer dose applied at planting.

Topdressing

Fertilizer application after crop emergence.

Fertigation

Applying dissolved fertilizer through irrigation water.

Urea

46 % N solid fertilizer; hygroscopic, fully soluble.

Anhydrous Ammonia

82 % N gas fertilizer injected into soil under pressure.

Ammonium Sulfate

20 % N fertilizer also supplying ~24 % S; hygroscopic.

Ordinary Superphosphate (OSP)

20 % P₂O₅ fertilizer; about 85 % water-soluble P.

Triple Superphosphate (TSP)

Concentrated monocalcium phosphate fertilizer high in P.

Muriate of Potash

Potassium chloride fertilizer; highly soluble source of K₂O.

Soil Erosion

Detachment and transport of soil by water, wind, or gravity.

Raindrop Erosion

Soil particle detachment by impact of raindrops.

Sheet Erosion

Uniform removal of thin soil layer by rainfall and runoff.

Rill Erosion

Formation of small channels several centimeters deep by runoff.

Gully Erosion

Enlarged rills forming channels too large for machinery crossing.

Stream Erosion

Removal of soil from sides and bed of streams.

Geologic Erosion

Natural background rate of soil removal matched by formation (~1 mm yr⁻¹).

Accelerated Erosion

Human-induced soil loss faster than soil formation (~10 mm yr⁻¹).

USLE

Universal Soil Loss Equation A=0.224 RKLSCP estimating annual soil loss.

Rainfall Erosivity Factor (R)

USLE factor representing climatic impact based on rain intensity and energy.

Soil Erodibility Factor (K)

USLE factor expressing inherent susceptibility of soil to erosion.

Slope Length Factor (L)

USLE factor adjusting for influence of slope length.

Slope Gradient Factor (S)

USLE factor adjusting for influence of slope steepness.

Cover-Management Factor (C)

USLE ratio of soil loss under given crop/cover to that under bare soil.