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Irrigation Association Certified Agricultural Irrigation Specialist Agricultural Drainage Engineering: practice questions

Irrigation Association Certified Agricultural Irrigation Specialist (CAIS) · USA · Irrigation Association

Original practice questions written to the published syllabus · not past papers
10worked here, free
18written to this exam in this subject
4syllabus units

About Irrigation Association Certified Agricultural Irrigation Specialist

Irrigation Association Certified Agricultural Irrigation Specialist (CAIS) is a professional certification run by Irrigation Association, for candidates in USA. 100 MCQs, 3 hours.

Source: irrigation.org.

Checked against the exam body's published information. Formats and fees change; confirm the current edition there before you book.

Agricultural Drainage Engineering in Irrigation Association Certified Agricultural Irrigation Specialist

Removing excess water and salt: surface and subsurface drain design, and reclaiming saline and sodic land.

Our 18 Irrigation Association Certified Agricultural Irrigation Specialist questions in this subject: 5 easy, 11 medium, 2 hard, across 4 units.

10 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

These 10 were written to Irrigation Association Certified Agricultural Irrigation Specialist and are not shown on any other exam's page.

Question 1 · medium

Using Rhoades's formula (FAO 29), LR = ECw/(5ECe - ECw), find the leaching requirement for water of ECw = 1.5 dS/m and a crop threshold ECe of 4.0 dS/m.

  1. 37.5 %
  2. 7.5 %
  3. 8.1 %
  4. 7.0 %
Answer and working

C. 8.1 %

LR = 1.5 / (5 x 4.0 - 1.5) = 1.5 / 18.5 = 0.081 = 8.1 %. 37.5 % is ECw/ECe; 7.5 % drops the minus ECw; 7.0 % adds it instead of subtracting.

Question 2 · hard

A field receives 800 mm of irrigation water of EC 1.5 dS/m in a season. Using TDS (mg/L) = 640 x EC (dS/m), how much salt is added per hectare?

  1. 0.77 t
  2. 77 t
  3. 12 t
  4. 7.7 t
Answer and working

D. 7.7 t

Volume = 0.8 m x 10,000 m2 = 8,000 m3. TDS = 640 x 1.5 = 960 mg/L = 0.96 kg/m3. Salt = 8,000 x 0.96 = 7,680 kg = 7.7 t/ha. The 0.77 and 76.8 options are factor-of-ten slips in depth or area. The 640 factor varies roughly 550-700 with ionic composition. 12 t uses 1,000 mg/L per dS/m instead of 640 (8,000 m3 x 1.5 kg/m3).

Question 3 · medium

A crop has salt-tolerance threshold 6.0 dS/m and slope 7.1 % per dS/m (Maas-Hoffman). What relative yield is expected at ECe = 9.0 dS/m?

  1. 36.1 %
  2. 21.3 %
  3. 57.4 %
  4. 78.7 %
Answer and working

D. 78.7 %

Y = 100 - b(ECe - a) = 100 - 7.1 x (9.0 - 6.0) = 78.7 %. 36.1 % ignores the threshold; 21.3 % is the loss, not the yield; 57.4 % subtracts the threshold instead of the excess.

Question 4 · easy

The sodium adsorption ratio of an irrigation water is:

  1. Na / (Ca + Mg), with all concentrations in mg/L
  2. (Ca + Mg) / Na, in mmol/L
  3. Na / sqrt(Ca + Mg + K), in mg/L
  4. Na / sqrt((Ca + Mg)/2), with all concentrations in meq/L
Answer and working

D. Na / sqrt((Ca + Mg)/2), with all concentrations in meq/L

SAR = Na / sqrt((Ca + Mg)/2) in meq/L. Using mg/L or omitting the square root and the factor 2 gives wrong values.

Question 5 · medium

Irrigation water contains Na 18 meq/L, Ca 5 meq/L and Mg 3 meq/L. What is its SAR?

  1. 6.36
  2. 2.25
  3. 4.5
  4. 9.0
Answer and working

D. 9.0

SAR = 18 / sqrt((5 + 3)/2) = 18 / sqrt(4) = 9.0. 6.36 forgets to halve (Ca + Mg); 2.25 omits the square root and the halving; 4.5 halves but forgets the square root.

Question 6 · hard

A water analysis reports Na 414 mg/L, Ca 100 mg/L and Mg 36.45 mg/L. What is the SAR? (Equivalent weights: Na 23, Ca 20.04, Mg 12.15.)

  1. 50.1
  2. 9.0
  3. 12.7
  4. 6.37
Answer and working

B. 9.0

Convert: Na = 414/23 = 18.0 meq/L; Ca = 100/20.04 = 4.99; Mg = 36.45/12.15 = 3.00. SAR = 18.0 / sqrt((4.99 + 3.00)/2) = 9.0. Using mg/L directly gives 50.1; using mmol/L for Ca and Mg gives 12.7; forgetting the /2 gives 6.37.

Question 7 · medium

Water has CO3 1.0, HCO3 5.5, Ca 2.0 and Mg 1.5 meq/L. What is its RSC and its class under the widely used USDA limits?

  1. 3.0 meq/L, unsuitable
  2. 3.0 meq/L, safe
  3. 2.0 meq/L, marginal
  4. 10.0 meq/L, unsuitable
Answer and working

A. 3.0 meq/L, unsuitable

RSC = (CO3 + HCO3) - (Ca + Mg) = 6.5 - 3.5 = 3.0 meq/L, above 2.5, so unsuitable. 2.0 omits carbonate; 10.0 adds instead of subtracting. Limits: < 1.25 safe, 1.25-2.5 marginal, > 2.5 unsuitable; some countries use their own limits.

Question 8 · medium

Using the Handbook 60 relation ESR = -0.0126 + 0.01475 SAR and ESP = 100 ESR/(1 + ESR), what equilibrium ESP corresponds to SAR = 12?

  1. 16.4 %
  2. 12.0 %
  3. 14.1 %
  4. 17.7 %
Answer and working

C. 14.1 %

ESR = -0.0126 + 0.177 = 0.1644; ESP = 100 x 0.1644 / 1.1644 = 14.1 %. 16.4 % stops at ESR x 100; 12 % assumes ESP equals SAR; 17.7 % drops the intercept and the conversion.

Question 9 · medium

Under FAO Paper 29 guidelines, what degree of restriction on use applies to irrigation water of ECw = 1.8 dS/m for salinity hazard?

  1. None
  2. Severe
  3. Slight to moderate
  4. Water is unusable for any crop
Answer and working

C. Slight to moderate

FAO 29: none below 0.7 dS/m, slight to moderate 0.7-3.0, severe above 3.0 dS/m. Even severe-restriction water can be used for tolerant crops with leaching and drainage.

Question 10 · medium

Why can very low-salinity water (for example ECw 0.1 dS/m) cause infiltration problems even at a moderate SAR?

  1. Low-salinity water contains more sodium relative to calcium and magnesium
  2. Low electrolyte concentration lets clay disperse and the surface crusts
  3. Pure water raises soil pH to above 10
  4. Low-salinity water freezes more readily
Answer and working

B. Low electrolyte concentration lets clay disperse and the surface crusts

Flocculation depends on salt concentration as well as sodium proportion; at the same SAR, purer water disperses clay more. FAO 29 therefore reads infiltration hazard from SAR and ECw together.

A study plan for Agricultural Drainage Engineering in Irrigation Association Certified Agricultural Irrigation Specialist

This plan follows where our questions actually fall, so the time goes where the marks are likely to be. It is our reading of the syllabus, not the exam body's weighting.

  1. First, the heavy units (89% of the 18 questions): Irrigation water quality: EC, SAR and RSC (9, 50%); Salinity and the leaching requirement (7, 39%).

    Read the manual chapters for these first and do every worked question you can find on them.

  2. Then the middle band: Drainage coefficient (1, 6%); Subsurface drain spacing: Hooghoudt and Ernst (1, 6%).

    Aim for one sitting per unit, then mixed questions across them.

  3. Leave time for the hard ones: Salinity and the leaching requirement (1 hard of 7), Irrigation water quality: EC, SAR and RSC (1 hard of 9).

    Come back to these after a first pass, untimed, and read every explanation, including for the options you rejected.

  4. Bank the easy marks: Irrigation water quality: EC, SAR and RSC (3 easy of 9); Salinity and the leaching requirement (2 easy of 7).

    Do these early in revision so they are fast on the day.

  5. Finish timed. Sit the subject as a timed set without notes, mark it, and send each wrong answer back to its unit above.

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