CCA Irrigation Management and Water Use 2 — Questions and Answers
Question 1: Irrigation water with an Electrical Conductivity (ECw) greater than 3.0 dS/m is classified as:
- Low salinity — suitable for most crops
- Medium salinity — requires moderate leaching
- High salinity — requires good drainage and salt-tolerant crops (Correct answer)
- Very high salinity — generally unsuitable for irrigation
Correct answer: High salinity — requires good drainage and salt-tolerant crops
Water with ECw of 3.0–6.0 dS/m is classified as high salinity and can be used only with good drainage management and salt-tolerant crops, as it poses significant osmotic stress risk.
Question 2: The leaching fraction in saline soil management is defined as the:
- Ratio of soil EC to irrigation water EC
- Fraction of applied irrigation water that drains below the root zone (Correct answer)
- Percentage of irrigation water lost to evaporation
- Proportion of rainfall that recharges the water table
Correct answer: Fraction of applied irrigation water that drains below the root zone
The leaching fraction is the portion of applied water that percolates below the root zone, carrying accumulated salts out of the crop root zone to prevent toxic buildup.
Question 3: Sodium Adsorption Ratio (SAR) of irrigation water is used to assess the risk of:
- Heavy metal toxicity to crops
- Soil structure degradation due to sodium-induced clay dispersion (Correct answer)
- Boron toxicity in sensitive crops
- Increased weed pressure from waterlogged soils
Correct answer: Soil structure degradation due to sodium-induced clay dispersion
High SAR causes sodium to displace calcium and magnesium on cation exchange sites, leading to clay dispersion, reduced infiltration, surface crusting, and loss of soil structure.
Question 4: Subsurface tile drainage is primarily installed to:
- Increase irrigation water storage in the root zone
- Remove excess water from saturated soils to improve aeration and trafficability (Correct answer)
- Prevent lateral movement of nutrients to field edges
- Reduce evapotranspiration demand on irrigated crops
Correct answer: Remove excess water from saturated soils to improve aeration and trafficability
Tile drainage removes gravitational water from saturated soils, improving soil aeration for root development, trafficability for field operations, and reducing waterlogging stress on crops.
Question 5: A center-pivot irrigation system with a flow rate of 800 gpm covering 125 acres has an application rate calculated to be 0.5 in/hr. The primary concern at this application rate is:
- Underapplication causing crop water stress
- Application rate exceeding soil infiltration rate causing runoff (Correct answer)
- Excessive deep percolation and nutrient leaching
- Freezing of water in the lateral pipes during night operation
Correct answer: Application rate exceeding soil infiltration rate causing runoff
When application rate exceeds the soil's infiltration rate, water ponds on the surface and runs off, reducing irrigation efficiency, causing erosion, and potentially carrying nutrients off-field.
Question 6: Regulated deficit irrigation (RDI) is a strategy where:
- Crops are irrigated to 100% ET replacement throughout the season
- Irrigation is intentionally withheld during drought-tolerant growth stages to save water without significant yield loss (Correct answer)
- Water is applied only through subsurface drip systems
- Fields are irrigated based solely on calendar date rather than crop need
Correct answer: Irrigation is intentionally withheld during drought-tolerant growth stages to save water without significant yield loss
RDI deliberately applies less water than full ET replacement during growth stages when crops are relatively tolerant to mild water stress, reducing total water use while minimizing yield impact.
Question 7: The primary advantage of using NDVI-based remote sensing imagery for irrigation management is:
- It directly measures soil water matric potential across a field
- It identifies spatial variability in crop water stress and canopy health to guide variable-rate irrigation (Correct answer)
- It replaces the need for weather station ET data entirely
- It measures the quantity of water applied by sprinkler systems
Correct answer: It identifies spatial variability in crop water stress and canopy health to guide variable-rate irrigation
NDVI imagery detects variations in crop vigor and canopy stress across a field, allowing crop advisors to identify under- or over-irrigated zones and prescribe variable-rate irrigation applications.
CCA Irrigation Management and Water Use 2
Irrigation water with an Electrical Conductivity (ECw) greater than 3.0 dS/m is classified as: