NCEA L1 Ag & Hort flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cation exchange capacity

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

Soil texture

The relative proportions of sand, silt and clay particles in a soil. It affects water holding, drainage and aeration and cannot be changed easily by management.

Soil structure

The arrangement of soil particles into aggregates or peds. Good structure gives pore space for air, water and roots, and can be improved by adding organic matter.

Soil pH

A measure of soil acidity or alkalinity on a scale of 0 to 14. Most crop nutrients are most available between about pH 5.8 and 6.8.

Macronutrients

Elements needed by plants in large amounts: nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. Nitrogen, phosphorus and potassium are the main fertiliser inputs.

Nitrogen role in plants

Nitrogen is used to build proteins, chlorophyll and nucleic acids. Deficiency shows as pale or yellow older leaves and reduced leaf and stem growth.

Phosphorus role in plants

Phosphorus is used in energy transfer molecules such as ATP and in root development. Deficiency often shows as stunted growth and purplish leaves.

Potassium role in plants

Potassium regulates water movement, stomatal opening and enzyme activity. It improves fruit quality, drought tolerance and resistance to some diseases.

Photosynthesis equation

Six carbon dioxide molecules plus six water molecules plus light energy produce one glucose molecule and six oxygen molecules inside chloroplasts containing chlorophyll.

Respiration in plants

The breakdown of glucose to release energy for growth and maintenance, using oxygen and producing carbon dioxide and water. It happens day and night.

Transpiration

Loss of water vapour from leaves through stomata. It draws water and dissolved minerals up the xylem and cools the leaf but increases water demand.

Stomata

Pores on leaf surfaces controlled by guard cells. They open for carbon dioxide uptake and close under water stress, reducing both transpiration and photosynthesis.

Limiting factor

The input in shortest supply that caps production. Adding other inputs while one factor, such as water, remains limiting gives little or no yield increase.

Rumen fermentation

Microbes in the rumen break down plant fibre into volatile fatty acids that the ruminant absorbs as its main energy source, and build microbial protein.

Ruminant stomach order

Rumen, reticulum, omasum, abomasum. The abomasum is the true stomach where acid digestion of protein begins after rumen fermentation.

Ruminant methane production

Methane is produced by methanogens in the rumen as a by-product of fibre digestion. It is a greenhouse gas and represents lost dietary energy.

Feed conversion ratio

The amount of feed consumed divided by the liveweight gain produced. A lower ratio means the animal converts feed to body weight more efficiently.

Pasture residual

The amount of pasture dry matter left after grazing, commonly around 1,500 kg DM per hectare, which allows rapid regrowth of remaining leaf area.

Three-leaf grazing rule

Pasture should be grazed before it reaches about three to four leaves per tiller, because older leaves die and pasture quality declines.

Stocking rate

The number of animals carried per hectare. It drives pasture demand, and mismatching it to pasture growth causes overgrazing or wasted feed.

Dry matter

Feed weight after all water is removed. It allows fair comparison of feeds such as pasture, silage and grain with very different water contents.

Silage making

Preserving pasture or crop by anaerobic fermentation, where lactic acid bacteria lower pH and prevent spoilage. Air exclusion and rapid wilting are critical.

Hay making

Preserving forage by drying it to low moisture, usually below about 15 to 20 percent, so microbial growth and heating are prevented during storage.

Integrated pest management

A tiered approach using monitoring, biological control, cultural and physical methods before chemicals, which are applied only above an economic threshold.

Economic threshold

The pest population level at which the value of crop loss avoided exceeds the cost of control, triggering a control action.

Biological control

Using natural enemies such as predators, parasitoids or pathogens to reduce pest numbers. It requires knowledge of the pest life cycle and predator survival.

Crop rotation

Growing different crop species in sequence on the same land to interrupt pest and disease cycles, vary nutrient use and maintain soil structure.

Monoculture risk

Growing one species repeatedly increases build-up of host-specific pests, diseases and weeds and depletes specific nutrients, raising reliance on chemical inputs.

Eutrophication

Nutrient enrichment of waterways, mainly by nitrogen and phosphorus runoff, causing algal blooms, oxygen depletion and harm to aquatic life.

Riparian planting

Planting vegetation along stream banks to trap sediment and nutrients from runoff, stabilise banks and shade water, improving waterway health.

Nutrient budget

An account of nutrients entering and leaving a farm system. It shows whether nitrogen and phosphorus are accumulating or being lost to the environment.

Marginal analysis

Comparing the extra revenue from a management change with the extra cost it creates. The change is justified only when marginal revenue exceeds marginal cost.