BGCSE Agricultural Science 1517 key terms

The relative proportions of sand, silt and clay particles in a soil sample, determined after the larger gravel and stones are removed. It controls water holding, drainage, aeration and how easily roots can grow.

The way individual soil particles clump together into crumbs or aggregates, creating pores between them. Good structure allows air, water and roots to move freely, while poor structure causes compaction, crusting or waterlogging.

Dark, fully decomposed organic matter that remains in soil after plant and animal residues have broken down. It holds nutrients and water, buffers pH changes, improves structure and gives topsoil its dark colour.

A measure of how acidic or alkaline a soil is, expressed on a scale from 0 to 14 where 7 is neutral. Values below 7 are acidic, above 7 alkaline; pH strongly affects nutrient availability and crop choice.

The downward movement of dissolved nutrients and other soluble substances through the soil profile with percolating water. Heavy rain or over-irrigation can leach nitrogen and other mobile nutrients below the root zone.

Ploughing and planting along the contour lines of a slope rather than up and down the slope. Each furrow forms a small barrier that slows runoff, reducing soil erosion and improving water infiltration.

The planned sequence of different crops grown on the same plot over successive seasons. Rotating crops with different nutrient needs and pest susceptibilities interrupts pest cycles and helps maintain soil fertility.

Growing two or more crop species together in the same field at the same time. The mixture may use light, water and nutrients more efficiently and can reduce pest and disease spread, but complicates harvesting and spraying.

The process in which a seed absorbs water, its embryo resumes growth and a young shoot and root emerge from the seed coat, provided temperature, moisture and oxygen are suitable.

Moving young plants that were raised in a nursery bed or seed tray into the main field. It is done when seedlings are strong enough to survive, and needs careful handling, watering and correct spacing.

Any mechanical working of the soil, such as digging, ploughing or harrowing, carried out to prepare a seedbed, control weeds and incorporate residues. Excessive tillage damages soil structure and increases erosion risk.

Covering the soil surface with a layer of material such as dry grass, straw, plastic or crop residues. Mulch conserves moisture, suppresses weeds, moderates soil temperature and protects the surface from erosion.

A grazing animal such as a cow, goat or sheep that has a multi-chambered stomach and can digest fibrous plant material by fermentation with microbes in the rumen. Ruminants regurgitate food to chew it again.

The length of time between conception and birth in a pregnant animal. Knowing the gestation period lets a farmer calculate the expected calving, lambing or kidding date and prepare for it.

The thick, yellowish first milk produced in the days right after an animal gives birth. It is rich in antibodies and must be fed to the newborn soon after birth to give protection against disease.

The stage at which a young animal is gradually or abruptly stopped from suckling its mother and must eat solid feed instead. Timing affects growth, stress and the mother's return to breeding condition.

Removing animals from the herd or flock on purpose, usually because of poor productivity, infertility, disease or age. Culling improves the average quality of the breeding stock and controls numbers.

The number of animals kept on a given area of land over a period, usually expressed as animals or livestock units per hectare. It must match the available feed to avoid overgrazing.

Giving an animal a preparation that stimulates its immune system to develop protection against a specific disease without causing the illness. A planned vaccination programme prevents outbreaks and reduces losses.

Keeping newly bought or returning animals separate from the main herd or flock for a set period to observe them and prevent disease spread. It also applies to imported plants and plant products.

A serious contagious disease that a farmer or veterinarian must report immediately to the national veterinary authority when it is suspected, so control measures can be started quickly.

A strategy that combines several pest controls, including resistant varieties, cultivation, biological control and monitoring, and uses pesticides only when justified, so pests stay below damaging levels with minimum chemical use.

The pest population level at which the value of the crop being lost exceeds the cost of the control measure, so the farmer should act. Below it, spraying would waste money.

Using living organisms such as predators, parasites or pathogens to reduce pest populations. It can be a lasting, low-chemical approach but requires careful introduction and takes time to work.

The inherited ability of a pest population to survive doses of a pesticide that would normally kill it, developing after repeated exposure. Resistance makes sprays ineffective, so control must be varied.

A shaft on a tractor that uses the engine's power to drive attached implements and machines, such as rotary mowers, pumps or sprayers. The shaft must always be fitted with a guard.

Measuring and adjusting a sprayer so it applies the intended volume of spray per hectare or per plant evenly. Correct calibration prevents under-dosing, wasted chemical, crop damage and contamination of the environment.

The income from an enterprise minus the variable costs of that enterprise, calculated for one season or year. It does not subtract fixed costs, so comparisons between enterprises are more meaningful.

Farm expenses that do not change, or change very little, with the level of production, such as land rent, insurance, permanent labour and machinery depreciation. They must be met however small the harvest.

The level of output or price at which the total income of a farm enterprise equals its total costs, so there is neither profit nor loss. Knowing it helps planning.

Deliberately growing trees or shrubs together with crops or livestock on the same land. The trees supply timber, fruit, fodder and shade, and their roots and litter help conserve soil and water.

Enrichment of a water body with nutrients, usually nitrates and phosphates washed from fertilised fields, which causes excessive algae growth and later oxygen depletion that kills fish.

The variety of living organisms, including plants, animals and microorganisms, found in an area, together with the genetic variety within each species. It supports natural pest control, pollination and soil health.

A group of cultivated plants within a species that has been selected and bred for uniform, heritable characteristics such as yield, maturity period or disease resistance, and is given a distinct name.

The improved growth, size or yield shown by the first-generation offspring of a cross between two genetically different parent lines. The advantage usually falls off in later generations of seed.

Cutting away selected shoots, branches or roots of a plant to shape its growth, remove damaged or diseased wood, improve light penetration and air movement, or balance vegetative growth with fruiting.

Joining a piece of stem or bud from one plant, the scion, onto the root system of another, the rootstock, so they grow as one plant. It combines fruit quality with strong roots and disease tolerance.

The number of seeds in a sample that produce normal seedlings, expressed as a percentage of the total number sown. It tells the farmer how densely to sow to get the desired plant stand.

A square frame of known area placed at random in a field or pasture to count plants, pests or ground cover within it. Repeating this at several places gives an estimate for the whole area.