RBSE SS Voc Micro-Irrigation Tec flashcards

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

Available water capacity

The water held between field capacity and permanent wilting point in the root zone. Calculated as field capacity minus permanent wilting point, expressed in mm per metre of soil depth.

Management allowed depletion

The fraction of available water a crop may use before irrigation is scheduled. Commonly 0.5 for field crops and 0.25 to 0.4 for sensitive horticultural crops.

Crop evapotranspiration

Water lost from the field through soil evaporation and plant transpiration. Estimated as the crop coefficient Kc multiplied by reference evapotranspiration ETo.

Basic infiltration rate

The steady rate at which a soil accepts water. Application rate of any irrigation system must stay below this value to prevent runoff and ponding.

Pressure-compensating emitter

An emitter that maintains a nearly constant rated flow over a wide pressure range, typically 0.5 to 4 bar, allowing long laterals and uneven terrain.

Fertilizer injection point

The location in the head works where fertilizer is introduced. It must be upstream of the filters and downstream of a check valve to prevent backflow.

Flush valve

A valve or removable end cap at the end of a lateral or sub-main that allows sediment and debris to be discharged periodically, protecting emitters from clogging.

Inline versus online emitters

Inline emitters are built into the tubing at fixed factory spacing; online emitters are punched into a plain lateral at any chosen spacing during installation.

Emission uniformity

A measure of how evenly emitters discharge water, calculated from manufacturer's coefficient of variation and number of emitters per plant. Target is 90 percent or higher.

Distribution uniformity

The ratio of the average flow of the lowest quarter of emitters to the mean emitter flow, multiplied by 100. It reflects real field performance.

Wetted percentage

The proportion of the field surface wetted by the drip system, calculated from wetted width and lateral spacing. Typically 30 to 60 percent for row crops.

Allowable pressure variation

The permitted difference in pressure along a lateral, commonly plus or minus 10 percent of nominal emitter pressure, which limits maximum lateral length.

Sprinkler application rate

Sprinkler discharge in litres per hour divided by the product of sprinkler spacing and lateral spacing in square metres. It must not exceed soil infiltration rate.

Christiansen uniformity coefficient

A sprinkler uniformity measure based on the sum of absolute deviations from mean catch depth. Values of 84 percent or above are generally acceptable for field crops.

Wetted diameter rule

Sprinkler spacing along the lateral should not exceed 60 percent of wetted diameter, and lateral spacing should not exceed 65 percent, for acceptable uniformity.

Wind effect on sprinklers

Wind above about 3 metres per second distorts the sprinkler pattern, reduces uniformity and increases drift loss. Night irrigation and closer spacing reduce the effect.

Pump duty point

The flow and head at which the pump curve intersects the system curve. It must match the design flow and pressure for uniform irrigation.

Cavitation

Formation and collapse of vapour bubbles when available net positive suction head falls below the pump requirement, causing noise, vibration, reduced flow and impeller damage.

Sand media filter

A pressure vessel containing graded sand that removes organic and inorganic particles down to roughly 40 to 50 microns. Cleaned by backwashing when pressure differential rises.

Venturi injector

A fertigation device that uses a pressure difference to draw fertilizer solution into the irrigation line. Simple and inexpensive, but causes a head loss.

Fertigation flushing rule

Inject fertilizer during the middle third of the irrigation cycle, then flush the lines with clean water for at least 10 to 15 minutes to prevent clogging.

Filter pressure differential

The difference in pressure across a filter. A rise of about 0.5 bar above the clean-filter baseline indicates the filter needs backwashing or cleaning.

Chlorination for clogging

Injection of chlorine to maintain 1 to 2 ppm free residual at the lateral end for 30 to 60 minutes to control organic and bacterial clogging, followed by flushing.

Acid treatment for scaling

Injection of dilute acid to bring irrigation water pH to about 4 to 5, dissolving calcium carbonate scale in emitters and laterals, followed by thorough flushing.

Leaching requirement

The fraction of irrigation water that must pass below the root zone to control salinity, estimated as ECw divided by five times ECe minus ECw.

Iron and manganese in water

Concentrations above about 0.5 ppm iron and 0.1 ppm manganese promote bacterial slime and precipitation, requiring oxidation or aeration before drip irrigation.

Electrical conductivity of water

A measure of dissolved salts. Values above about 1 dS/m may stress sensitive crops and require leaching, crop selection or blending with better water.

Payback period

Total investment divided by annual net benefit from yield gain, water and energy savings minus maintenance. It shows how many years the system takes to repay itself.

PMKSY Per Drop More Crop

The Indian government micro-irrigation subsidy component that shares system cost between centre and state, with higher support for small and marginal farmers.

Benefit-cost ratio

The present value of benefits divided by the present value of costs. A ratio above one indicates the micro-irrigation investment is economically viable.

Acid dilution safety rule

Always add acid slowly to water, never water to acid, because the reaction is strongly exothermic and can cause violent spattering and burns.

Lockout before pump service

Isolate electrical power, close valves and release residual pressure before servicing a pump, filter or valve to prevent electric shock and sudden water release.

Emitter flow field check

Collect water from a known number of emitters for a measured time at the head, middle and tail of a lateral and convert to litres per hour to detect clogging.