Test 18 - Soil-Water-Plant Relationships

Question 1 ప్రశ్న 1

In irrigation engineering, what is meant by the effective root zone of a crop?

A The soil layer lying below the groundwater table only B The soil depth from which the crop extracts a major part of the water required for growth C The full geological thickness of soil down to bedrock D The depth wetted by the largest historical flood

Question 2 ప్రశ్న 2

Which condition best describes a saturated soil?

A Only the smallest pores contain water and all large pores contain air B The water content is exactly equal to permanent wilting point C Essentially all pore spaces are filled with water, apart from possible small amounts of entrapped air D The soil contains only hygroscopic water

Question 3 ప్రశ్న 3

Which description most accurately defines field capacity of a well-drained agricultural soil?

A The soil-water content remaining after excess gravitational water has drained and downward drainage has become relatively slow B The soil-water content at which all plant roots permanently stop extracting water C The condition in which every pore is filled with water under positive pressure D The moisture content of an oven-dry soil

Question 4 ప్రశ్న 4

What is the permanent wilting point in the soil-water-plant system?

A The water content immediately after a heavy irrigation while the soil is saturated B The maximum water content that can be stored in the soil C The point at which all pore water becomes gravitational water D The soil-water content at which a plant can no longer extract sufficient water and remains wilted unless water is added

Question 5 ప్రశ్న 5

Which statement best describes hygroscopic water in soil?

A It is free water draining rapidly from macropores under gravity B It is water held very tightly as thin adsorbed films on soil particles and is generally unavailable to plants C It is all water stored between field capacity and permanent wilting point D It is water ponded temporarily on the soil surface

Question 6 ప్రశ్న 6

For irrigation calculations, what is total available water in the crop root zone?

A Water stored between saturation and field capacity only B All water contained in the soil including water below permanent wilting point C The water stored between field capacity and permanent wilting point over the effective root depth D Only the water applied during the most recent irrigation

Question 7 ప్రశ్న 7

Which expression correctly represents readily available water, RAW, when p is the allowable fraction of total available water that can be depleted before significant crop water stress begins?

A RAW = p × TAW B RAW = TAW / p² C RAW = FC + PWP D RAW = p / TAW

Question 8 ప్రశ్న 8

A soil has volumetric water content at field capacity of 0.32 and at permanent wilting point of 0.14. If the effective root depth is 0.80 m, what is the total available water in the root zone?

A 72 mm B 96 mm C 120 mm D 144 mm

Question 9 ప్రశ్న 9

A crop has an effective root depth of 1.20 m in a uniform soil with θFC = 0.30 and θPWP = 0.18. What is the total available soil water?

A 96 mm B 144 mm C 180 mm D 360 mm

Question 10 ప్రశ్న 10

For the soil in the previous type of calculation, TAW is 144 mm. If the allowable depletion fraction p is 0.50, what is the readily available water?

A 36 mm B 48 mm C 72 mm D 144 mm

Question 11 ప్రశ్న 11

A root zone is 0.90 m deep. Its volumetric water content at field capacity is 0.30 and its current volumetric water content is 0.22. Neglecting losses, what net irrigation depth is required to restore the root zone to field capacity?

A 72 mm B 80 mm C 90 mm D 108 mm

Question 12 ప్రశ్న 12

A uniform root zone has θFC = 0.30, θPWP = 0.15 and current volumetric water content θ = 0.21 over a depth of 0.80 m. How much plant-available water remains above permanent wilting point?

A 24 mm B 36 mm C 72 mm D 48 mm

Question 13 ప్రశ్న 13

A soil has gravimetric moisture contents of 25% at field capacity and 12% at permanent wilting point. Its dry bulk density is 1.40 Mg/m³, water density may be taken as 1.00 Mg/m³, and effective root depth is 0.80 m. What is the total available water depth?

A 104.0 mm B 145.6 mm C 182.0 mm D 260.0 mm

Question 14 ప్రశ్న 14

A soil has gravimetric water content of 24% at field capacity and 16% at the time irrigation is to be applied. Dry bulk density is 1.50 Mg/m³ and the effective root depth is 0.60 m. Taking water density as 1.00 Mg/m³, what net depth is required to refill the root zone to field capacity?

A 48 mm B 60 mm C 72 mm D 120 mm

Question 15 ప్రశ్న 15

A two-layer root zone consists of 0.40 m of soil with θFC = 0.30 and θPWP = 0.15, underlain by 0.60 m with θFC = 0.28 and θPWP = 0.16. What is the total available water in the full root zone?

A 132 mm B 120 mm C 108 mm D 150 mm

Question 16 ప్రశ్న 16

For the same two-layer root zone, current volumetric water contents are 0.22 in the upper 0.40 m and 0.20 in the lower 0.60 m. What net depth is required to restore both layers to field capacity?

A 48 mm B 64 mm C 72 mm D 80 mm

Question 17 ప్రశ్న 17

A field requires a net irrigation depth of 60 mm to refill the crop root zone. If field application efficiency is 75%, what gross depth must be applied at the field inlet, neglecting other conveyance losses?

A 45 mm B 80 mm C 90 mm D 135 mm

Question 18 ప్రశ్న 18

For the same uniform soil with unchanged θFC and θPWP, what happens to total available water in the root zone if the effective rooting depth increases from 0.60 m to 0.90 m?

A It becomes one-half of its former value B It remains unchanged because soil texture is unchanged C It increases by 50%, assuming the additional depth has the same soil properties D It necessarily triples

Question 19 ప్రశ్న 19

What normally happens when a freely drained soil is wetted to saturation and then allowed to drain without further inflow?

A Gravitational water drains from the larger pores and the soil water content approaches field capacity B The soil immediately becomes oven dry C The soil water content falls directly below permanent wilting point D All hygroscopic water is removed by gravity

Question 20 ప్రశ్న 20

Why is routine irrigation designed to refill the active root zone approximately to field capacity rather than deliberately maintaining an ordinary upland crop soil at saturation?

A Because plants can use water only when all pores contain air B Because field capacity is always equal to permanent wilting point C Because saturation contains no water available to plants D Because water substantially above field capacity tends to drain and prolonged saturation can reduce root-zone aeration

Question 21 ప్రశ్న 21

Two soils have the same field-capacity water content, but Soil X has a much higher permanent wilting-point water content than Soil Y. Which soil has the larger available-water capacity, assuming equal root depth?

A Soil X, because a higher wilting point always increases available water B Soil Y, because available water is the difference between field capacity and permanent wilting point C They must have identical available-water capacity D No comparison is possible even when both moisture limits are given

Question 22 ప్రశ్న 22

A crop root zone has TAW = 120 mm and the allowable depletion fraction p = 0.40. If root-zone depletion has reached 55 mm, which interpretation is most appropriate under this scheduling criterion?

A The soil is necessarily saturated B The crop has not yet used any readily available water C The depletion has exceeded RAW = 48 mm, so irrigation is due if the aim is to avoid significant water stress D The soil must already be below permanent wilting point

Question 23 ప్రశ్న 23

A net root-zone deficit of 72 mm is to be replenished over an irrigated area of 2.0 hectares. Neglecting application losses, what volume of water must be stored in the soil?

A 1440 m³ B 720 m³ C 3600 m³ D 14,400 m³

Question 24 ప్రశ్న 24

Consider the following statements about soil-water-plant relationships: I. Field capacity is below saturation in a freely drained soil. II. Permanent wilting point is the lower conventional limit of plant-available water. III. Total available water in a uniform root zone is proportional to θFC - θPWP and effective root depth. IV. Readily available water is generally only a fraction of total available water. Which option is correct?

A I and II only B I, II and III only C II, III and IV only D I, II, III and IV

Question 25 ప్రశ్న 25

A crop is grown in a soil with TAW = 160 mm. The selected readily available fraction is p = 0.50, and current root-zone depletion is 70 mm. No rainfall is expected. What is the most appropriate interpretation?

A The crop is already at permanent wilting point B The depletion is still below RAW = 80 mm, but irrigation should be planned before depletion materially exceeds about 80 mm if the chosen no-stress criterion is to be maintained C The soil must be above field capacity D The next irrigation should be delayed until depletion reaches the full 160 mm in every case

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