NSSCAS Agricultural Science 8222 key terms

The relative proportions of sand, silt and clay particles in a soil. It controls water holding capacity, drainage, aeration and how easily the soil can be cultivated.

The way individual soil particles bind together into aggregates, creating pores. Good structure allows roots, air and water to move freely and resists erosion and compaction.

A measure of the acidity or alkalinity of soil on a scale from 0 to 14. It strongly affects the availability of plant nutrients and the activity of soil organisms.

The ability of a soil, mainly through clay and organic matter, to hold positively charged nutrient ions such as calcium, magnesium and potassium and release them to plant roots.

The amount of water a soil retains after excess water has drained away by gravity. It represents the upper limit of water readily available to plants between irrigations or rains.

The soil moisture level below which plants can no longer extract water and wilt permanently. Soil water between field capacity and this point is plant-available water.

The downward movement of water through soil carrying dissolved nutrients and salts below the root zone. It can waste fertiliser and pollute groundwater, especially on sandy soils.

The detachment and removal of topsoil by wind or water. It reduces fertility, soil depth and yield, and is controlled by cover crops, contour farming, terracing and windbreaks.

The squeezing together of soil particles so that pore space is reduced. It restricts root growth, water infiltration and drainage, and is often caused by heavy machinery or overgrazing.

The build-up of soluble salts in the root zone to levels that harm crops. It results from poor drainage, excessive irrigation and high evaporation, and is a serious risk in dry Namibian irrigation schemes.

The quantity of agricultural lime needed to raise soil pH to a target level for a chosen crop. It is determined from soil tests of acidity and soil texture.

Collecting representative soil from a field, usually as a composite of several cores, for laboratory analysis. Correct sampling depth and pattern are essential for reliable fertiliser recommendations.

Covering the soil surface with organic or inorganic material to reduce evaporation, suppress weeds, moderate temperature and protect against erosion. It also adds organic matter when it decomposes.

Any tillage system that leaves crop residue on the soil surface and disturbs soil minimally. It reduces erosion, conserves moisture and protects soil structure compared with repeated ploughing.

Ploughing and planting along the contour lines of a slope rather than up and down it. The ridges slow runoff and trap water and soil, reducing water erosion.

Growing different crops in a planned sequence on the same land over successive seasons. It interrupts pest and disease cycles, manages soil fertility and reduces reliance on a single crop.

Growing two or more crops together in the same field at the same time. It can improve land use, spread risk and improve soil cover, but requires careful spacing and nutrient management.

Leaving a field uncultivated for one or more seasons to allow moisture and nutrients to recover. In dry areas it is mainly used to store soil water for the next crop.

The number of plants of a crop per unit area, determined by row spacing and within-row spacing. It affects competition for light, water and nutrients and therefore final yield.

The resumption of growth by a seed, ending with the emergence of the radicle and shoot. It requires adequate moisture, suitable temperature and, for some species, light or darkness.

The proportion of seeds in a lot that are alive and capable of germinating under favourable conditions. It is checked by a germination test before planting to set sowing rates.

A rate and type of fertiliser advised for a specific crop and field, based on soil test results, crop requirement and expected yield. It balances nutrient supply against cost and environmental risk.

A pest control approach that combines monitoring, cultural, biological and chemical methods, using pesticides only when economic thresholds are exceeded. It reduces cost, resistance and environmental harm.

The pest population level at which the value of crop loss it causes exceeds the cost of controlling it. It guides farmers on when spraying is justified.

The inherited ability of a pest population to survive a pesticide dose that would normally kill it. It develops through repeated use of the same chemical and is managed by rotating active ingredients.

The minimum time that must pass between the last application of a veterinary drug or pesticide and the sale of milk, eggs, meat or crop produce. It protects consumers from harmful residues.

Administering a vaccine to stimulate an animal's immune system and protect it against a specific disease. It is a core part of herd health programmes and must follow the cold chain.

A disease that must by law be reported to veterinary authorities when suspected. Rapid reporting allows movement control and containment, protecting animal health and trade.

The isolation of newly arriving or sick animals to prevent the spread of disease to the rest of the herd or flock. It is also applied to restrict movement during disease outbreaks.

An organism such as a roundworm, tapeworm or fluke that lives inside an animal's body and feeds at its expense. Control relies on strategic deworming, grazing management and faecal monitoring.

An organism such as a tick, mite, louse or flea that lives on the outside of an animal and feeds on blood or skin. Ticks also transmit serious diseases such as heartwater.

A chemical used to kill ticks and mites on livestock. Correct concentration, application method and rotation of chemical groups are needed to avoid resistance and residues.

The ability of internal parasites to survive doses of deworming drugs that would normally kill them. It is managed by correct dosing, rotating drug groups and reducing unnecessary treatment.

The number of animals of a given class kept on a unit of land, usually expressed as hectares per large stock unit. It must match available grazing to prevent overgrazing.

The maximum number of animals an area of land can support sustainably without degradation of vegetation and soil. It varies with rainfall, season and grazing management.

Moving livestock between separate paddocks in a planned cycle so that each area rests and regrows. It improves pasture recovery and reduces selective overgrazing and parasite build-up.

A standard measure of livestock feed requirement, based on a mature cow of about 450 kilograms gaining weight on good pasture. It allows different species and classes to be compared.

The total feed given to an animal over 24 hours. A balanced ration supplies energy, protein, minerals, vitamins and water in the proportions needed for the animal's production stage.

The kilograms of feed consumed divided by the kilograms of liveweight gain or product produced. A lower ratio means more efficient feed use and better profitability.

Gross income from an enterprise minus its variable costs. It measures the profitability of an enterprise and helps farmers compare options and plan rotations.

A cost that changes with the level of production, such as seed, fertiliser, fuel and casual labour. Variable costs are subtracted from gross income to calculate gross margin.

A cost that does not change with the level of production in the short term, such as land rent, insurance or depreciation on machinery. Fixed costs must be covered for a farm to be profitable.

The level of output or price at which total income equals total costs, so the enterprise makes neither profit nor loss. It is used to judge the risk of a production plan.

The gradual loss in value of machinery, equipment or buildings through use, age and obsolescence. It is treated as a farm cost and used to plan replacement.

The difference between the price the consumer pays and the price the farmer receives for the same product. It covers transport, processing, storage and trader profit.

Processing or packaging a raw farm product to increase its market value, such as milling grain or grading meat. It can raise income but requires investment and market access.

Deciding when and how much water to apply to a crop, using soil moisture, crop demand or weather data. Good scheduling saves water, prevents leaching and supports yield.

Applying water slowly and directly to the root zone through small emitters in pipes. It uses water efficiently and limits evaporation and weed growth but needs filtration and maintenance.

Adjusting and checking equipment such as sprayers, seeders or fertiliser spreaders so they deliver the intended rate evenly. Correct calibration prevents waste, crop damage and environmental contamination.

Adjusting farming practices to reduce the harm expected from changing climate conditions, such as drought-tolerant crops, early planting, water harvesting and diversified enterprises.

Actions taken to reduce the impact of drought, including water harvesting, mulching, fodder storage, reduced stocking and choosing early maturing varieties. It aims to protect income and resources.

Collecting and storing rainfall runoff for later crop or livestock use, for example in earth dams, tanks or micro-catchments. It reduces risk in dry areas with erratic rainfall.