USA · Irrigation Association · professional
100 MCQs, 3 hours.
For irrigation managers and specialists rather than designers.
Official source: https://www.irrigation.org/IA/FileUploads/IA/Certification/CertificationCandidateHandbook.pdf
Original questions written to this exam's published syllabus and pattern. Not past papers.
1. A drip designer has a clay loam field and a loamy sand field. For the same emitter discharge, in which field should emitter spacing along the lateral generally be closer to give a continuous wetted strip?
B. The loamy sand, because water spreads less laterally and moves more vertically
In coarse soils gravity dominates over capillarity, so the wetted bulb is narrow and deep and emitters must be closer. Fine soils spread water further sideways. Lateral spread depends on soil as well as discharge, and the reason given in the bulk-density option is wrong.
Soil Science for Engineers · Soil texture and structure
2. If irrigation water is limited to a single application for an irrigated wheat crop in north-west India, textbook recommendations favour applying it at which stage?
B. Crown root initiation, about three weeks after sowing
Crown root initiation (commonly about 20–25 days after sowing in Indian conditions) is cited as the most critical stage for the first irrigation in wheat; stress then reduces tillering and root growth. Water at physiological maturity is too late to add yield; dough stage is late grain filling, of less benefit than CRI; a pre-sowing irrigation alone leaves the crop dry at its first critical stage.
Crop Production & Protection for Engineers · Crop classification and seasons
3. A clay loam has volumetric field capacity 0.32 and wilting point 0.14. With a 1.2 m root zone and a management allowed depletion of 50 %, what is the readily available water?
D. 108 mm
TAW = 1000 × (0.32 − 0.14) × 1.2 = 216 mm. RAW = 0.5 × 216 = 108 mm. 216 mm is TAW, not RAW; 192 mm applies MAD to field capacity alone; 84 mm applies it to the wilting point water, which is unavailable.
Irrigation Engineering (Soil-Water-Plant, Conveyance, Surface Methods) · Soil-water-plant relations: field capacity, wilting point and MAD
4. On a centre pivot with sprinklers at equal spacing along the lateral, how must the discharge of each sprinkler vary with its distance r from the pivot to apply a uniform depth?
A. In proportion to r
Each sprinkler at radius r with spacing s serves an annulus of area about 2πr·s per revolution, so for equal depth its discharge must be proportional to r. Discharge proportional to r² would be the case only if the ring area grew with r², which it does not for a fixed spacing.
Sprinkler & Micro-Irrigation Systems · Sprinkler types and components
5. A rainfall of 30 mm percolates to a shallow water table in a soil of drainable porosity 0.06. By how much does the water table rise?
B. 0.50 m
Rise = recharge / drainable porosity = 0.030 m / 0.06 = 0.50 m. Multiplying (30 x 0.06 = 1.8 mm) is the common error; 0.05 m and 5 m are decimal slips. Small drainable porosity means a small recharge causes a large rise.
Agricultural Drainage Engineering · Drainage coefficient
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