RBSE SS Voc Micro-Irrigation Tec key terms

The amount of water a soil holds after excess water has drained away by gravity, usually one to three days after rain or irrigation. It is the upper limit of water easily available to plants.

The soil moisture level at which plants can no longer extract water and wilt permanently, because the remaining water is held too tightly by soil particles. Irrigating before this point is essential.

The water held in soil between field capacity and permanent wilting point, expressed as depth of water per depth of soil. It depends mainly on soil texture and organic matter content.

The portion of available water that a crop can take up without stress, often 40 to 60 percent of available water capacity. It sets the allowable depletion used to schedule irrigation.

The water loss by evaporation and transpiration from a standard well-watered grass surface, calculated from weather data such as temperature, humidity, wind and solar radiation. Crop water use is estimated by multiplying it by a crop coefficient.

A dimensionless factor that adjusts reference evapotranspiration to a specific crop at a specific growth stage. Values rise from establishment through peak canopy and decline near maturity.

Deciding when and how much to irrigate, based on crop water demand, soil moisture status and system capacity. Good scheduling avoids both under-watering and wasteful deep percolation.

The percentage of water delivered by a system that is stored in the crop root zone and usable by the crop. Losses come from evaporation, runoff, deep percolation and wind drift.

A measure of how evenly water is applied across a field or between emitters. It is calculated by comparing the lowest quarter of measured application depths with the average depth.

A small device fitted on or inside a drip lateral that releases water at a controlled low rate, typically 1 to 8 litres per hour. Emitters may be inline, online, pressure-compensating or non-compensating.

An emitter that maintains a nearly constant discharge over a wide range of inlet pressures, typically 0.5 to 4 bar. It allows longer laterals and more level-independent uniform application.

The thin flexible pipe, usually 12 to 20 mm diameter, carrying water to emitters along a crop row. Laterals connect to submain through a grommet, barb or connector and end with a flush valve.

A pipe that distributes water from the mainline to a group of drip laterals or sprinkler lines. It is usually laid along the headland and sized to keep friction loss within design limits.

The primary pipeline carrying water from the pumping or filtration point to the submains. It is sized for the full design flow with acceptable friction loss and pressure rating.

The assembly at the water source that includes the pump, filters, valves, pressure gauge, flow meter and often the fertigation injector. It conditions water before it enters the distribution network.

Removing suspended particles from irrigation water using sand media filters, screen filters, disc filters or combinations. Correct selection depends on source water quality and emitter sensitivity to clogging.

Blockage of emitter passages by mineral precipitates, algae, silt or organic matter, which reduces flow and uniformity. Prevention relies on filtration, chemical treatment and regular flushing.

Opening the ends of laterals, submains or mains to release accumulated sediment and debris at higher velocity. Routine flushing is a core maintenance task that protects emitters from clogging.

Injecting soluble fertiliser into the irrigation stream so nutrients are delivered with water directly to the root zone. It requires a backflow prevention device and careful control of concentration and timing.

A fertiliser injection device that uses a pressure difference to draw concentrate into the water line. It is simple and pump-independent but creates a pressure loss and needs a minimum flow.

A device or arrangement that stops irrigation water, fertiliser or chemicals from flowing back into the water source or public supply. It is a mandatory safety requirement in fertigation systems.

Adding chlorine, usually as sodium hypochlorite, to irrigation water to control algae, bacteria and slime that clog emitters. Dosage and contact time must be controlled to avoid crop damage.

A pressure surge caused by sudden changes in water velocity, such as rapid valve closure or pump stop. It can burst pipes and fittings, so air valves and slow-closing valves are used.

A valve that releases trapped air from pipelines during filling and admits air during draining to prevent vacuum collapse. It protects pipes from air locks and water hammer damage.

The total pressure a pump must develop, equal to the sum of static lift, discharge elevation, friction losses and required operating pressure at the outlet. It determines pump selection.

A graph showing the relationship between flow rate and head produced by a pump at a given speed. The duty point is where the pump curve meets the system curve.

The pressure at which a system is designed to run, measured at the emitter, sprinkler or reference point. Deviations change flow rate and reduce uniformity.

A device that holds downstream pressure at a set value despite upstream variation. It protects drip laterals and sprinkler blocks from excess pressure and improves emission uniformity.

A measure of how evenly emitters discharge water across a drip system, accounting for manufacturing variation and pressure differences. Values above about 85 percent are generally considered good.

The distance between sprinklers along a lateral and between laterals, chosen to match wetted diameter and wind conditions. Correct spacing ensures overlapping patterns and uniform application.

The depth of water a sprinkler system delivers per unit time, usually in millimetres per hour. It must not exceed the soil infiltration rate to avoid runoff and ponding.

A classic index of sprinkler application uniformity calculated from catch-can depths. It expresses average depth as a percentage of the mean, with higher values indicating more even distribution.

Pressure lost as water flows through pipes and fittings due to resistance. It increases with flow rate, pipe length and roughness, and must be added when sizing pumps and pipelines.

The extra fraction of irrigation water needed to push accumulated salts below the root zone. It is higher when irrigation water is saline and drainage is poor.

A measure of the water's ability to conduct electricity, used as an indicator of dissolved salt concentration. High values warn of salinity risk to crops and emitters.

Laboratory or field analysis of irrigation water for pH, hardness, salinity, suspended solids, iron, manganese and biological content. Results guide filter choice and chemical treatment.

The flow and head at which a pump actually operates, found where the pump curve crosses the system curve. Operating far from the design duty point wastes energy and can damage the pump.

Workplace practices that protect installers and operators from hazards such as electrical shock, chemical exposure, trench collapse and machinery injury. It includes use of PPE and safe procedures.

Gear worn to reduce exposure to workplace hazards, such as gloves, goggles, boots, helmets and respirators. It is the last line of defence after eliminating or controlling the hazard.

A procedure for isolating and tagging energy sources, such as pumps and electrical panels, before maintenance. It prevents accidental start-up or release of stored energy while work is in progress.