Answer: A. Timing and water amount. Irrigation scheduling determines when water should be applied and how much to apply.
When should irrigation begin to prevent water stress?
A When runoff begins
B Only after leaves dry
C Before critical soil-water depletion
D After final harvest
Answer: C. Before critical soil-water depletion. Irrigation is generally timed before root-zone depletion reduces crop evapotranspiration below its potential.
Which processes together make crop evapotranspiration?
A Drainage plus leaching
B Photosynthesis plus pollination
C Infiltration plus runoff
D Transpiration plus evaporation
Answer: D. Transpiration plus evaporation. Crop evapotranspiration combines water transpired by plants with evaporation from soil and plant surfaces.
FAO estimates crop evapotranspiration by combining reference ET with what?
A A seed purity score
B A crop coefficient
C A soil color index
D A harvest price
Answer: B. A crop coefficient. In the FAO approach, crop evapotranspiration is estimated from reference evapotranspiration multiplied by a crop coefficient.
When effective rainfall meets the crop’s full water need, what is irrigation need?
A A fixed monthly amount
B Zero
C One full irrigation
D Twice the rainfall
Answer: B. Zero. If effective rainfall supplies the full crop water need, no additional irrigation is required.
What makes rainfall effective for crop water supply?
A Water stored and available
B Water that runs off
C Rain falling outside fields
D Rain measured at a station
Answer: A. Water stored and available. Effective rainfall is the portion of precipitation that infiltrates and can be used by the crop.
Rainwater that flows off the soil surface is called what?
A Capillary rise
B Surface runoff
C Deep percolation
D Transpiration
Answer: B. Surface runoff. Runoff is water flowing over the soil surface instead of entering the soil.
What does field capacity describe?
A Permanent crop wilting
B Soil completely saturated
C Water below the root zone
D Water remaining after free drainage
Answer: D. Water remaining after free drainage. Field capacity is the water content remaining after excess gravitational water has drained away.
Which condition defines the permanent wilting point?
A Roots begin to branch
B Water enters dry seed
C Plants cannot recover turgor
D Soil is fully saturated
Answer: C. Plants cannot recover turgor. At the permanent wilting point, plants cannot regain turgidity even when placed in a humid environment.
Plant-available water lies between which soil-water limits?
A Saturation and runoff
B Field capacity and wilting point
C Rainfall and evaporation
D Infiltration and drainage
Answer: B. Field capacity and wilting point. Available water is generally the difference between water content at field capacity and at the permanent wilting point.
For a given soil, what can a deeper root zone increase?
A Emitter pressure
B Rainfall intensity
C Conveyance losses
D Potential water storage
Answer: D. Potential water storage. A deeper effective root zone can access a greater volume of soil water, if roots can explore that soil.
Which instrument indicates soil-water tension?
A Tensiometer
B Anemometer
C Hydrometer
D Rain gauge
Answer: A. Tensiometer. A tensiometer measures soil-water tension within its operating range.
What does gravimetric soil-moisture analysis compare?
A Rainfall and runoff
B Crop yield and price
C Seed weight and purity
D Wet soil and dry soil
Answer: D. Wet soil and dry soil. The gravimetric method determines water content from the mass difference before and after drying a soil sample.
Why can a fixed irrigation calendar over-irrigate?
A Soil texture stays unknown
B Crop roots never change
C Weather and field conditions vary
D Rainfall is always zero
Answer: C. Weather and field conditions vary. Crop demand and soil moisture change with weather and growth, so a rigid schedule may apply too much or too little water.
Where does drip irrigation place water through emitters?
A Near the root zone
B Only at field edges
C Below every drainage pipe
D Across the whole canopy
Answer: A. Near the root zone. Drip irrigation delivers water locally near plants through emitters.
How does sprinkler irrigation apply water?
A Flows through open furrows
B Sprays water like rainfall
C Fills a level basin
D Moves only below ground
Answer: B. Sprays water like rainfall. Sprinklers distribute water through the air so it reaches the field in droplets.
Surface irrigation generally moves water across land using what?
A Capillary action alone
B Gravity
C Compressed air
D Plant transpiration
Answer: B. Gravity. Surface methods use gravity to move water over the soil surface.
Furrow irrigation carries water through channels placed where?
A Between crop rows
B Along the canopy
C Under storage floors
D Inside seed containers
Answer: A. Between crop rows. Furrows are small channels that convey water between rows of crops.
Which irrigation method suits a level plot enclosed by small bunds?
A Drip irrigation
B Center-pivot irrigation
C Basin irrigation
D Subsurface drainage
Answer: C. Basin irrigation. Basin irrigation retains water within a level enclosed area.
Which factors should guide irrigation method selection?
A Harvest date alone
B Seed color, label, price
C Farm name and road
D Soil, slope, crop, water
Answer: D. Soil, slope, crop, water. Method choice depends on local soil, slope, crop, water availability, labor, technology, and cost.
Why are filters installed in drip systems?
A Prevent emitter clogging
B Measure rainfall directly
C Raise soil temperature
D Increase crop salinity
Answer: A. Prevent emitter clogging. Filters remove particles that could block small emitter openings.
What does a clogged emitter most directly cause?
A Higher seed purity
B Local under-watering
C Faster crop maturity
D More uniform wetting
Answer: B. Local under-watering. A clogged emitter reduces local discharge and can leave nearby plants short of water.
Uneven pipeline pressure can cause what?
A Automatic salt removal
B More effective rainfall
C Uniform root growth
D Uneven water application
Answer: D. Uneven water application. Pressure differences can alter discharge and reduce distribution uniformity.
Strong wind during sprinkler irrigation can cause what?
A Higher field capacity
B Less evaporation always
C Drift and uneven coverage
D Deeper seed placement
Answer: C. Drift and uneven coverage. Wind can move sprinkler droplets away from their intended pattern and make application uneven.
How is application efficiency calculated?
A Diverted water ÷ rainfall
B Runoff ÷ crop yield
C Root-zone water stored ÷ applied
D Water applied ÷ soil depth
Answer: C. Root-zone water stored ÷ applied. Application efficiency compares water stored in the root zone for crop use with the water applied.
Conveyance efficiency compares which amounts?
A Delivered water and diverted water
B Runoff and evaporation
C Stored water and crop yield
D Rainfall and root depth
Answer: A. Delivered water and diverted water. Conveyance efficiency is delivered water divided by the amount diverted or pumped into the conveyance system.
Why assess distribution uniformity separately from efficiency?
A Uniformity measures seed purity
B Some areas may be under-watered
C Both always mean the same
D Efficiency identifies every crop
Answer: B. Some areas may be under-watered. A system may store much of the applied water yet distribute it unevenly across the field.
Why are young seedlings often irrigated in small, frequent amounts?
A They have no transpiration
B Their soil is always saturated
C They need no oxygen
D Their roots are shallow
Answer: D. Their roots are shallow. Young plants have shallow roots and low water use, so smaller, more frequent applications may suit early growth.
As roots deepen and crop water use rises, what adjustment may be suitable?
A Water only after harvest
B Smaller, more frequent amounts
C No irrigation for the season
D Larger, less frequent applications
Answer: D. Larger, less frequent applications. FAO guidance describes larger and less frequent applications during stages with greater evapotranspiration and deeper roots.
After rainfall, what should be checked before irrigating again?
A Soil moisture and effective rain
B Farm boundary length
C Harvest market price
D Seed tag color
Answer: A. Soil moisture and effective rain. Effective rainfall and current soil moisture help determine whether more irrigation is needed.
Deep percolation describes water moving where?
A Across the soil surface
B Into the leaf canopy
C Below the crop root zone
D Back into the atmosphere
Answer: C. Below the crop root zone. Deep percolation is water moving beneath the effective crop root zone.
Excess irrigation runoff wastes water and can cause what?
A Improved uniformity
B Soil erosion
C Seed dormancy
D Higher germination
Answer: B. Soil erosion. Runoff wastes applied water and can carry soil and nutrients away.
How can prolonged waterlogging harm crop roots?
A It removes all soil salts
B It restricts oxygen supply
C It prevents all weeds
D It increases root respiration
Answer: B. It restricts oxygen supply. Saturated soil has limited air-filled pore space, restricting oxygen available to roots.
What is the main purpose of field drainage?
A Increase irrigation depth
B Raise seed moisture
C Remove excess water
D Prevent all evaporation
Answer: C. Remove excess water. Drainage removes excess surface or subsurface water from the root zone.
Why might additional water be used on saline soil?
A Flush salts below roots
B Seal the soil surface
C Increase salt concentration
D Stop all infiltration
Answer: A. Flush salts below roots. Leaching moves soluble salts below the root zone when suitable drainage can carry them away.
What must accompany leaching to avoid salt accumulation?
A More surface runoff
B Higher fertilizer rates
C Continuous flooding
D Adequate drainage
Answer: D. Adequate drainage. Without drainage, leached salts may remain in or return to the root zone.
On slowly infiltrating clay soil, which application approach helps limit runoff?
A Apply water faster
B Keep soil permanently flooded
C Use a lower application rate
D Ignore field slope
Answer: C. Use a lower application rate. Applying water no faster than the soil can absorb it helps limit ponding and runoff.
Crop water need is 6 mm and effective rainfall is 2 mm. Ignoring other contributions, what irrigation remains?
A 8 mm
B 4 mm
C 2 mm
D 6 mm
Answer: B. 4 mm. Simplified irrigation need equals crop water need minus effective rainfall: 6 mm minus 2 mm is 4 mm.
What does deficit irrigation deliberately do?
A Irrigates only after harvest
B Replaces crop rotation
C Supplies excess water daily
D Applies less than full need
Answer: D. Applies less than full need. Deficit irrigation intentionally supplies less than the full crop water requirement, often prioritizing selected stages.
If 100 mm is applied and 75 mm is stored in the root zone, what is application efficiency?
A 75 percent
B 25 percent
C 50 percent
D 100 percent
Answer: A. 75 percent. Application efficiency is stored root-zone water divided by applied water: 75 ÷ 100 = 75 percent.
Why protect water supply near flowering in sensitive crops?
A It supports reproductive development
B It changes soil texture
C It increases seed dormancy
D It prevents all lodging
Answer: A. It supports reproductive development. Water stress around flowering can impair reproductive processes and reduce grain or fruit set in sensitive crops.
What advantage comes from using soil readings with crop stage?
A It guarantees maximum yield
B It replaces drainage
C Timing reflects current conditions
D It removes all irrigation losses
Answer: C. Timing reflects current conditions. Soil-water measurements combined with crop stage make irrigation decisions responsive to actual field needs.
How can surface mulch influence irrigation demand?
A It increases wind drift
B It reduces soil evaporation
C It raises runoff speed
D It removes crop roots
Answer: B. It reduces soil evaporation. Mulch can reduce direct evaporation from the soil surface and conserve moisture.
Why level a field before surface irrigation?
A Remove the need for scheduling
B Increase emitter pressure
C Change seed variety
D Improve water distribution
Answer: D. Improve water distribution. A better leveled field can support more even water advance and distribution in surface systems.
As soil dries, what generally happens to soil-water tension?
A It changes into rainfall
B Tension magnitude increases
C It measures crop yield
D It always becomes zero
Answer: B. Tension magnitude increases. As soil water becomes harder for roots to extract, measured tension generally increases within the instrument’s range.
What can measuring flow from drip emitters reveal?
A Seed genetic purity
B Crop harvest date
C Rainfall effectiveness
D Uneven emitter delivery
Answer: D. Uneven emitter delivery. Comparing emitter discharge can reveal clogging, pressure problems, or uneven system performance.
Excessive irrigation may leach which nutrients below roots?
A Mobile nutrients such as nitrate
B All soil organic matter
C Atmospheric nitrogen only
D Seed-coat minerals
Answer: A. Mobile nutrients such as nitrate. Excess water can move mobile nutrients such as nitrate below the root zone.
At 10 liters per minute for 30 minutes, what volume is delivered?
A 100 liters
B 3,000 liters
C 300 liters
D 30 liters
Answer: C. 300 liters. Volume equals flow rate multiplied by time: 10 liters per minute × 30 minutes = 300 liters.
Why keep records of irrigation amounts and crop response?
A Change crop seed genetics
B Eliminate weather variation
C Improve future scheduling decisions
D Replace water measurement
Answer: C. Improve future scheduling decisions. Records allow farmers to compare applied water and crop response when refining future schedules.
What does irrigation water productivity relate?
A Crop output per water used
B Drainage per soil color
C Rainfall per farm worker
D Water pressure per seed
Answer: A. Crop output per water used. Water productivity relates agricultural output to the water consumed or applied, depending on the stated measure.