NCEA Level 3 Ag & Hort Science key terms

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

The way soil particles clump together into aggregates, creating pore spaces. Good structure allows air, water and roots to move freely, while poor structure restricts drainage and root growth.

The ability of a soil, mainly through clay and organic matter, to hold positively charged nutrient ions and release them to plant roots. Higher capacity generally means greater nutrient retention.

The downward movement of soluble nutrients and other substances through soil with draining water. It removes mobile nutrients such as nitrate from the root zone and can pollute groundwater.

A measure of soil acidity or alkalinity on a scale from 0 to 14. It strongly affects which nutrients stay available to plants and which soil organisms can thrive.

Ground limestone or related material applied to soil to raise pH and reduce acidity. It also supplies calcium and can improve the availability of several nutrients.

An element that plants need in relatively large amounts, such as nitrogen, phosphorus, potassium, sulfur, calcium and magnesium. Deficiencies usually limit growth quickly.

An element plants need only in very small amounts, such as iron, zinc, copper, manganese, boron and molybdenum. Shortages still cause distinct deficiency symptoms.

The extent to which nutrients in soil exist in forms plant roots can take up. It depends on factors such as pH, moisture, organic matter and soil texture.

A material applied to supply nutrients to plants. Fertilisers may be mineral or organic, and are described by their nitrogen, phosphorus and potassium content.

The enrichment of water with nutrients, often nitrate and phosphate from farmland runoff. It causes excessive algae growth, oxygen depletion and harm to aquatic life.

A vegetated buffer zone along a stream, river or drain. It traps sediment and nutrients, stabilises banks and shades waterways, reducing farm impacts on water quality.

The wearing away and movement of soil by water, wind or gravity. It removes fertile topsoil, reduces productivity and can damage waterways and infrastructure.

A line on the land connecting points of equal elevation. Cultivating or planting along contours slows water flow and reduces soil erosion on sloping ground.

Mechanical working of the soil, as in ploughing or cultivating. It prepares a seedbed and controls weeds but can damage structure and increase erosion and organic matter loss.

The squeezing together of soil particles so pore space is reduced. It restricts water infiltration, air movement and root penetration, often caused by heavy machinery or stock.

Material in soil derived from living things, including plant residues, roots and soil organisms in various stages of decay. It improves structure, water holding and nutrient supply.

The dark, stable, fully decomposed portion of soil organic matter. It holds moisture and nutrients and gives soil its crumbly, friable character.

The conversion of atmospheric nitrogen gas into forms plants can use. Legumes do this through bacteria in root nodules, and some free-living soil microbes also fix nitrogen.

A plant of the pea and bean family that forms a partnership with nitrogen-fixing bacteria in root nodules. Legumes are used in pastures and rotations to add nitrogen to soil.

Growing different crops in a planned sequence on the same land. It helps control pests and diseases, balances nutrient use and can improve soil condition.

Growing a single crop species over a large area or for successive seasons. It can be efficient but tends to increase pest, disease and soil fertility problems.

A strategy that combines monitoring, biological control, cultural practices and carefully targeted chemicals to keep pests below damaging levels. It aims to reduce reliance on pesticides.

Using living organisms such as predators, parasites or pathogens to reduce pest populations. It is a key tool in integrated pest management and can reduce chemical use.

The pest population level at which the cost of control is justified by the value of crop saved. It guides decisions about when to act against a pest.

The inherited ability of a pest population to survive doses of a pesticide that would normally kill it. It develops through selection pressure and can make products ineffective.

A substance used to kill or inhibit fungi that cause plant diseases. Repeated use can lead to resistance, so it is normally combined with other disease management methods.

The process by which green plants use light energy to convert carbon dioxide and water into sugars, releasing oxygen. It is the basis of crop growth and yield.

The breakdown of sugars to release energy for plant processes, using oxygen and producing carbon dioxide and water. It continues day and night and consumes some of the products of photosynthesis.

The loss of water vapour from plant leaves through small pores called stomata. It draws water and nutrients up from the roots and cools the plant.

The drooping of leaves and stems when water loss exceeds uptake, so plant cells lose their firmness. It signals water stress and can reduce growth and yield.

Supplying water to crops artificially when rainfall is insufficient. Good scheduling matches water supply to crop demand while avoiding waste and leaching.

The mass of plant material remaining after all water has been removed. It is used to measure growth, feed value and crop yield without the variation caused by moisture content.

The total leaf area of a crop above a unit area of ground, expressed as a ratio. It indicates how much light the canopy can intercept and therefore potential growth.

Managed grassland grazed by livestock. Its quality and quantity depend on species mix, season, fertiliser use and grazing management, and it is the main feed on many farms.

The number of animals carried on a given area of land over a period. Matching it to feed supply helps avoid overgrazing and maintains pasture performance.

Meeting present needs for food and fibre without reducing the ability of future generations to do the same. It balances economic, environmental and social considerations in farming.