UPMSP Intermediate Agricultural Chemistry key terms

The capacity of a soil to supply essential plant nutrients in adequate amounts and correct proportions, supported by suitable physical conditions, so that crops can complete their life cycle and yield well.

The actual yield a soil delivers under a given management system, combining inherent fertility with climate, crop variety, water supply and farming practices; it is measured in output, not nutrient supply alone.

The fraction of a nutrient in soil that a growing plant can absorb during its life cycle, usually the soil solution plus easily exchangeable forms; it is what soil tests try to estimate.

The soil test value below which a profitable crop response to added fertilizer is expected; above it, added nutrient rarely pays. It converts a laboratory number into a practical recommendation.

The numerical result a laboratory reports for a nutrient extracted from a soil sample by a specified method; it is meaningful only with the method and calibration used to obtain it.

The total quantity of exchangeable cations a soil can hold on clay and humus surfaces, expressed in centimoles of charge per kilogram; it governs retention of calcium, magnesium, potassium and ammonium against leaching.

The percentage of the cation exchange capacity occupied by basic cations such as calcium, magnesium, potassium and sodium rather than by hydrogen and aluminium; higher values generally indicate a less acidic, more fertile soil.

The proportion of the cation exchange capacity occupied by sodium ions, expressed as a percentage; high values indicate sodic soil with poor structure and restricted water movement.

The negative logarithm of hydrogen ion activity in the soil solution, measured in water or dilute salt suspension; it indicates acidity or alkalinity and strongly controls nutrient availability and microbial activity.

The resistance of a soil to change in pH when acid or alkali is added, arising mainly from clay and organic matter; highly buffered soils need much more lime or gypsum to shift pH.

The quantity of agricultural lime needed to raise the pH of a plough-layer soil to a target value suited to the crop, determined by exchangeable acidity or by buffer-pH tests.

The amount of gypsum needed to replace exchangeable sodium in a sodic soil with calcium and so restore structure and permeability; it is estimated from the exchangeable sodium to be removed.

A nutrient that a plant cannot complete its life cycle without, whose function cannot be replaced by another element and which acts directly in plant metabolism. Seventeen are recognised for higher plants.

An essential element required by plants in relatively large amounts, conventionally nitrogen, phosphorus, potassium, calcium, magnesium and sulphur; each is expressed as a percentage of dry matter.

An essential element needed by plants in very small amounts, namely iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel; deficiency and toxicity can both occur within narrow ranges.

The principle that crop growth is limited by whichever essential factor is in shortest supply relative to need, so adding other nutrients cannot raise yield until that limiting factor is corrected.

The principle that each additional unit of a growth factor produces a smaller yield increase than the previous unit once other factors are fixed, so fertilizer response curves flatten at higher rates.

Applying nutrients in proportions that match crop requirement and soil supply, so that no single nutrient is over- or under-applied; it usually improves nutrient use efficiency and reduces waste.

The guaranteed nutrient content of a fertilizer, conventionally stated as the percentages of nitrogen, available phosphorus expressed as phosphorus pentoxide, and water-soluble potassium expressed as potassium oxide.

A fertilizer material that supplies predominantly one nutrient, such as urea for nitrogen or muriate of potash for potassium, though it may carry other elements incidentally.

A fertilizer produced chemically so that each granule contains two or more nutrients in a fixed ratio, for example diammonium phosphate; the nutrients cannot be separated physically.

Physical mixing of dry granular fertilizers, without chemical reaction, to obtain a desired nutrient ratio; the blend can segregate during handling and store poorly if components are incompatible.

The proportion of applied nitrogen recovered in the harvested crop or removed from the soil-plant system; it falls with excessive rates, poor timing, volatilization, leaching and denitrification losses.

Loss of nitrogen as ammonia gas from the soil surface, especially when urea or ammonium fertilizers are applied to warm, moist, alkaline or high-lime soils without incorporation.

Downward movement of soluble nutrients, chiefly nitrate and sulphate, below the root zone with percolating water; it wastes fertilizer and can pollute groundwater.

The microbial oxidation of ammonium to nitrite and then nitrate in aerobic soil, carried out by specialised bacteria; it acidifies soil and produces nitrate that is easily leached or denitrified.

A chemical added to ammonium or urea fertilizers that slows bacterial conversion of ammonium to nitrate, reducing leaching and denitrification losses and sometimes improving nitrogen use efficiency.

Material of plant or animal origin, such as farmyard manure, compost or green manure, added to soil mainly to supply organic matter and nutrients slowly while improving physical and biological properties.

Stabilised, humus-rich material produced by controlled aerobic decomposition of organic residues, used as a soil amendment and slow nutrient source; maturity matters because immature compost can harm roots.

A crop grown specifically to be incorporated into the soil while still succulent, adding organic matter and nitrogen, especially when the species is a legume fixing atmospheric nitrogen.

The ratio of carbon mass to nitrogen mass in an organic material; low ratios favour rapid net release of nitrogen, high ratios cause microbes to immobilise nitrogen temporarily during decomposition.

Temporary uptake of available mineral nitrogen by soil microorganisms as they decompose carbon-rich residues, reducing nitrogen supply to the crop until decomposition and microbial turnover release it again.

Conversion of organic nitrogen or other organically bound nutrients into inorganic forms by microbial decomposition, making them available for plant uptake and for loss processes.

The dark, relatively stable fraction of soil organic matter remaining after decomposition, contributing to cation exchange, water retention, aggregation and buffering of soil pH.

Combining mineral fertilizers with organic manures, biofertilizers and appropriate crop practices to sustain yields while maintaining soil fertility and limiting nutrient losses to the environment.

A preparation containing live microorganisms, such as rhizobia, azotobacters or phosphate-solubilising bacteria, that improves nutrient supply to plants through biological activity rather than through added nutrient mass.

The prepared commercial product in which an active ingredient is combined with carriers, solvents, surfactants or adjuvants to make it safe, stable and convenient to dilute and apply.

The biologically effective chemical component of a pesticide product, stated as a percentage or mass per litre; dose calculations and residue limits refer to it, not to the formulated product.

A liquid formulation in which the active ingredient and emulsifier dissolve in an organic solvent and form an emulsion on dilution with water; it is easy to measure but uses flammable solvents and can damage sensitive crops.

A powder formulation in which the active ingredient is mixed with inert filler and wetting agents so that it disperses in water as a suspension for spraying; it needs agitation and leaves visible residue.

The minimum number of days permitted between the last pesticide application and harvest, set so that residues in the harvested produce fall below the maximum residue limit.

The legally permitted concentration of a pesticide residue in or on food or feed, based on good agricultural practice and toxicological assessment; it is not a safety threshold for long-term exposure.

Any trace of a pesticide, its metabolites or degradation products remaining in or on produce, soil or water after application; persistence depends on the compound, dose, formulation and environment.

Progressive build-up of a persistent substance such as an organochlorine pesticide in the tissues of organisms, increasing in concentration along a food chain and raising exposure for predators and humans.

Increase in the concentration of a persistent substance at each successive trophic level of a food chain, so top predators carry far higher tissue concentrations than the environment or their prey.

Nutrient enrichment of water bodies, mainly by nitrate and phosphate from fertilizers, manure and sewage, causing excessive algal growth, oxygen depletion and harm to aquatic life.

Accumulation in soil of harmful substances such as heavy metals, excess salts, pesticide residues or industrial wastes at concentrations that impair soil function, crop quality or food safety.

Use of living organisms, chiefly microorganisms and plants, to degrade, transform or remove contaminants from soil or water; it is usually slower than excavation but cheaper and less destructive.

Use of plants to extract, stabilise or degrade soil contaminants; hyperaccumulator species can remove heavy metals, and harvested biomass must then be safely disposed of.

A bulk soil sample made by mixing several small cores taken from one uniform area, from which a reduced subsample is sent to the laboratory to represent the field.

A sample collected so that it reflects the average composition of the whole lot or field being assessed; sampling error usually exceeds laboratory analytical error when it is done poorly.

A volumetric procedure in which a solution of known concentration is added from a burette until a reaction endpoint is reached, allowing the amount of an unknown substance to be calculated.

A solution whose concentration is accurately known, prepared from a primary standard or standardized against one, and used to calibrate instruments or to titrate unknowns.

A soluble complex in which an organic ligand binds a metal ion at two or more points, keeping micronutrients such as iron or zinc available to plants instead of precipitating in soil.