Irrigation Management and Water Use Flashcards

Irrigation water with an Electrical Conductivity (ECw) greater than 3.0 dS/m is classified as:

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.

The leaching fraction in saline soil management is defined as the:

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.

Sodium Adsorption Ratio (SAR) of irrigation water is used to assess the risk of:

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.

Subsurface tile drainage is primarily installed to:

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.

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:

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.

Regulated deficit irrigation (RDI) is a strategy where:

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.

The primary advantage of using NDVI-based remote sensing imagery for irrigation management is:

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.