Quiz 1

Question 1

Which of the following does NOT increase when soil water content is increased from wilting point to field capacity?

1. Gravimetric water content
2. Degree of saturation
3. Bulk density
4. Unsaturated hydraulic conductivity

Answer 1

3. Bulk density

Question 2

In a clay textured soil:

1. Structure affects saturated hydraulic conductivity more than it affects water holding capacity
2. Structure affects saturated hydraulic conductivity less than it affects water holding capacity
3. Structure affects saturated hydraulic conductivity and water holding capacity equally
4. Structure affects neither saturated hydraulic conductivity nor water holding capacity

Answer 2

1. Structure affects saturated hydraulic conductivity more than it affects water holding capacity

Question 3

In the estimation of rates of evapotranspiration, the crop factor takes into account variation in:

1. Humidity
2. Temperature
3. Plant growth stage
4. All of the above

Answer 3

3. Plant growth stage

Question 4

Plant available water is usually estimated as the difference in water content between wilting point and field capacity.

Which of the following phenomena can result in plants effectively having more water available to them than this?

1. High soil strength in clay soils reducing root growth at suctions below wilting point.
2. Low unsaturated hydraulic conductivity slowing drainage in sandy soils at suctions below field capacity.
3. High soil strength in sandy soils reducing root growth at suctions below wilting point
4. The presence of salts increasing total suction at field capacity.

Answer 4

2. Low unsaturated hydraulic conductivity slowing drainage in sandy soils at suctions below field capacity.

Question 5

Pores with diameters < 0.2 µm:

1. Are more abundant in sandy soils than clay soils
2. Hold the majority of plant-available water
3. Are more affected by soil texture than soil structure.
4. Are readily explored by root hairs.

Answer 5

3. Are more affected by soil texture than soil structure.

Question 6

Choose the correct statement:

1. Soil structural stability is always high in self-mulching soils
2. Soil structural stability can be improved by increasing cultivation
3. Soil structural stability is usually low in acid soils
4. Soil structural stability can be improved by increasing organic matter content

Answer 6

4. Soil structural stability can be improved by increasing organic matter content

Question 7

Choose the correct statement regarding the difference in composition of exchange cations between acid soils and neutral/alkaline soils:

1. Acid soils have a higher Na:Ca ratio than neutral or alkaline soils
2. Acid soils have a lower Na:Ca ratio than neutral or alkaline soils
3. Acid soils have a higher proportion of exchangeable Al than neutral or alkaline soils
4. The majority of exchange cations in acid soils are H⁺, whereas neutral and alkaline soils contain little exchangeable H⁺

Answer 7

3. Acid soils have a higher proportion of exchangeable Al than neutral or alkaline soils

I THINK - NEED TO CHECK!

Question 8

Which of the following is likely to contribute to soil acidification?

1. Inefficient nitrogen fertilisation
2. Inefficient phosphorus fertilisation
3. Inefficient potassium fertilisation
4. All of the above

Answer 8

1. Inefficient nitrogen fertilisation

Question 9

Which of the following is likely to reduce soil acidification?

1. Draining a wetland soil
2. Switching from an ammonium-based fertiliser to a urea-based fertiliser
3. Increasing the legume content of a pasture
4. Removing crop residues

Answer 9

2. Switching from an ammonium-based fertiliser to a urea-based fertiliser

Question 10

Choose the correct statement regarding soil organic carbon levels

1. Grassland soils generally have lower organic carbon levels than forest soils
2. Subsoils usually have higher organic carbon levels than topsoils
3. Permanently saturated soils usually have high carbon levels
4. Soils in hotter climates generally have higher carbon contents than soils with cooler climates

Answer 10

3. Permanently saturated soils usually have high carbon levels

Question 11

Using the following water retention curve:

1. Estimate the matric suction of the peat at a volumetric water content of 0.4.
2. The radius of the largest water-filled pores in the peat at a volumetric water content of 0.4
3. The volumetric water content of the peat at field capacity
4. The volumetric water content of the peat at wilting point
5. The volume of plant available water per hectare for the peat to a depth of 10 cm.

Answer 11

1. ~90 kPa
2. r=
3. Field capacity = 1 m head = 10 kPa = 0.78 m³/m³ = 78%
4. Wilting point = 150 m head = 1500 kPa = 0.15 m³/m³ = 15%
5. • Amount of soil:
   • 10 cm = 0.1 m
   • 1 ha = 10,000 m²
   • 10,000 m² / 0.1 m = 1,000 m³
     * PAW
   • = θ_v (1 m) - θ_v (150 m)
   • = 0.78 - 0.15
   • = 0.63 m³/m³ = 63%

Question 12

Using the following infiltration curves for five soils:

1. Estimate the steady-state infiltration rate for Horton 1
2. Which of the five soils would pond if water were added at a uniform rate of 20 mm per hour for 1 hour? Explain.
3. Which of the five soils would pond if water were added at a uniform rate of 20 mm per hour for 3 hours? Explain.
4. Which of the five soils do you suspect to have the highest clay content? Explain.
5. Estimate the depth of soil wetting for Horton 1 if water were added at a uniform rate of 20 mm per hour for 1 hour, if this soil has a porosity of 0.5 cm³/cm³ and the soil is at 80% saturation in the transmission zone.

Answer 12

1. • I = St^1/2 + At
   • I ≈ At
   • Over 1 hour (3-2), ~58-43 mm was infiltrated = 15 mm, ∴ I = 15 mm/hr