1. What is the size of the tile at an outlet of a 12 hectare drainage system, if the D.C is 2 cm and the tile grade is 0.5%. Assume the rugosity coefficient as 0.015 for the tile drain material.
a) 10 cm
b) 20 cm
c) 15 cm
d) 25 cm
Explanation: Volume of water passing the drain in one second = (1200/24 x 3600) = 1/72 m3/sec
Q = 1/72 m3/sec
Q = 1/n x A x R2/3 x S1/2
A = πD2/4, P = πD, R = A/P = D/4
1/72 = (1/0.015) x (πD2/4) x (D/4) x (0.5/100)
On solving the value of D = 17.4 cm
Use D = 20 cm.
2. Which type of alternate layouts system for tile drainage has two mains?
a) Grid Iron System
b) Natural System
c) Double main System
d) Herring Bone System
Explanation: This system has two mains with separate laterals for each main. This type of system is used when the bottom of depression is wide. It also helps in reducing the length of the laterals and eliminates the break in slope at the edge of the depression of the lateral.
3.How many cubic metres of water will be removed for this particular period of a system designed to use a D.C of 1.5 cm draining 20 hectares for a capacity of 5 days?
a) 10000 m3
b) 25000 m3
c) 15000 m3
d) 20000 m3
Explanation: D.C of 1.5 cm means that 1.5 cm of water depth will be removed from the drainage in 24 hours.
Volume of water entering the drain per day = (1.5/100) x 20 x 104 = 3000 m3/day
Volume of water passing the drain within 5 days of flow = 5 x 3000 = 15000 m3.
4. Which among the following salt is also called black alkali?
a) Na2CO3
b) Na2SO4
c) NaCl
d) NaOH
Explanation: Na2CO3 is present in excess in black alkali soils. It is known as a black alkali because it dissolves some organic constituents of soil which appears black in solution with it. The patches of black stain are generally spotted on the ground.
5. Which is the least harmful salt for agricultural soil?
a) Na2CO3
b) Na2SO4
c) NaCl
d) NaOH
Explanation: NaCl is found in excess in white-alkali soils. In this, salinity is caused by soluble salts other than alkali salts. The reaction between NaCl and soil (S) produces Na(S) and Cl– ion and the soluble products are leached away from the soil surface by drainage water.
6. Alkali soils are reclaimed by ___________
a) leaching of soil
b) using limestone as a soil amendment
c) using gypsum as a soil amendment
d) provision of drainage
Explanation: Alkali soils are best reclaimed by cationic exchange i.e. replacement of alkali from soil colloids by calcium ions. Application of gypsum in the soil reduces alkalinity to a great extent and makes the soil fertile. Good drainage leaches away the by-product of the reaction.
7. If the salt concentration of the irrigation water ranges from 0.5 – 2 g/L, then what is the restriction on its use?
a) No restriction on its use
b) It should be used with appropriate water management practices
c) It is not generally advised for use unless consulted with specialists
d) No dependency on the salt concentration
Explanation: If the salt concentration is less than 0.5 g/L, then there is no salinization risk and no restriction on the use of irrigation water. If the concentration is more than 2 g/L, there is high risk and is not generally advised for use. If the concentration is in between there is slight to moderate risk and it should be used with appropriate water management practices.
8. If the salt concentration of the soil water (saturation extract) in milli-mhos/cm is in between 4.5 – 9, then what is the salinity of the soil?
a) Non-saline
b) Slightly saline
c) Medium saline
d) Highly saline
Explanation: The salt concentration in the water extracted from a saturated soil defines the salinity of the soil.
| S.no | The salt concentration of soil water | Salinity |
|---|---|---|
| 1. | 0 – 4.5 milli-mhos/cm | Non-saline |
| 2. | 4.5 – 9.0 milli-mhos/cm | Slightly saline |
| 3. | 9.0 – 18 milli-mhos/cm | Medium saline |
| 4. | >18 milli-mhos/cm | Highly saline |
9.Solonchak soil is the other name for ____________
a) alkali Soils
b) sodic Soils
c) saline-alkali soils
d) saline soils
Explanation: Solonchak soil is also called white alkali or saline soils. They have an excessive concentration of natural soluble salts and low exchangeable sodium.
10. What are the three classes of salty soil?
a) Saline soil, Saline-alkali soil, Non-saline soil
b) Saline soil, Alkali soil, Non-saline soil
c) Saline soil, Alkali soil, Saline-alkali soil
d) Alkali soil, Non-saline soil, Saline-alkali soil
Explanation: The three classes are –
i. Saline or white alkali or solonchak soil- High soluble salts and low ESP
ii. Alkali or Sodic or black alkali soil – Low salt content but high ESP
iii. Saline-alkali soils – High salt content and High ESP.