Agronomy Irrigation and Water Management 2 — Questions and Answers
Question 1: What is the most critical growth period for corn when water stress causes the greatest yield loss?
- Germination and emergence
- V6 to V10 vegetative stage
- Silking through early grain fill (R1-R3) (Correct answer)
- Grain dry-down period
Correct answer: Silking through early grain fill (R1-R3)
Water stress at silking and early grain fill (R1-R3) can cause poor pollination, kernel abortion, and the greatest proportional yield loss in corn.
Question 2: What is the primary cause of soil salinity buildup in irrigated fields in arid regions?
- Excessive use of manure fertilizers
- Salt accumulation from irrigation water combined with inadequate leaching (Correct answer)
- High rainfall dissolving rock minerals
- Organic matter decomposition releasing salts
Correct answer: Salt accumulation from irrigation water combined with inadequate leaching
Irrigation water carries dissolved salts that accumulate in the root zone as water evaporates or is transpired, especially in arid climates with insufficient rainfall to leach salts.
Question 3: What is leaching requirement in irrigated agriculture?
- Amount of fertilizer needed per irrigation cycle
- Additional irrigation water needed to flush excess salts below the root zone (Correct answer)
- Volume of water needed to reach field capacity
- Drainage coefficient for tile drainage design
Correct answer: Additional irrigation water needed to flush excess salts below the root zone
Leaching requirement is the fraction of applied irrigation water that must pass through and below the root zone to prevent salt accumulation to damaging levels.
Question 4: Which irrigation scheduling method uses crop canopy temperature to detect plant water stress?
- Neutron probe monitoring
- Infrared thermometry (crop water stress index) (Correct answer)
- Electrical resistance blocks
- Gravimetric soil sampling
Correct answer: Infrared thermometry (crop water stress index)
The crop water stress index (CWSI) uses infrared thermometers to measure canopy temperature, since stressed plants close stomata and become warmer than well-watered plants.
Question 5: What is the primary benefit of subsurface tile drainage in humid regions?
- Reduces crop yield by lowering water table
- Removes excess water from root zone, allowing earlier field operations and better aeration (Correct answer)
- Increases irrigation water efficiency
- Prevents leaching of applied nutrients
Correct answer: Removes excess water from root zone, allowing earlier field operations and better aeration
Tile drainage removes excess soil water, improving soil aeration for root growth, allowing earlier spring field access, and reducing denitrification losses.
Question 6: Which management practice helps conserve soil moisture in dryland farming systems?
- Frequent tillage to break surface crust
- Leaving crop residue on the soil surface and minimizing tillage (Correct answer)
- Planting crops earlier in spring
- Applying gypsum to soil surface
Correct answer: Leaving crop residue on the soil surface and minimizing tillage
Crop residue mulch on the surface shades the soil, reduces evaporation, and improves water infiltration in dryland systems where stored moisture is critical.
Agronomy Irrigation and Water Management 2
What is the most critical growth period for corn when water stress causes the greatest yield loss?