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1

Discuss the features of clay soil that make it so reactive

Clay particles are shaped like thin and flat platelets, they are also very small which means they have a very large surface area. Clay also has a charge which is mostly negative which can attract positively charged ions

2

What is Vt?

The total volume of wet soil

3

What is Pb?

Bulk density. Large bulk density maybe because it is a sandy soil or it is very compact

4

What is Pw?

Density of water

5

What is Ms?

The mass of the oven-dry soil

6

What is Mw?

The mass of water. Can calculate by subtracting Ms from the mass of the wet soil

7

What is w?

The gravimetric water content

8

What is θsat?

The volumetric water content of soil when it is saturated. To calculate θsat = f

9

What is f?

Porosity

10

What is θfc?

The volumetric water content of soil when it is at field capacity. To calculate θfc = θsat - θmp

11

What is θmp?

The macroporosity. The volume of all the macropores

12

What is θ?

The volumetric water content

13

What is the minimum value of macroporosity for good aeration?

10%

14

What is the field capacity?

The micropores are full of water but the macropores have successfully drained

15

What is saturation?

All the pores are full of water

16

Which two soil constituents have the largest surface area?

Clay and organic matter (hummus)

17

What is z?

The effective root depth and should always be converted to mm

18

How do you calculate the readily available water holding capacity of soil?

(θfc - θsp) x z

19

How do you calculate the total available water holding capacity of soil?

(θfc - θpwp) x z

20

What is θsp?

The volumetric water content at the stress point

21

What is θpwp

The volumetric water content at the permanent wilting point

22

How is soil structure assessed in the field?

The extent to which aggregates have formed and stability of these aggregates to a force applied. The shape of the aggregates. The size of peds.

23

What is the permanent wilting point?

When the plants have extracted all the water they are capable of taking from the soil

24

Features of good soil structure are...

Small aggregates that are stable

25

What is the stress point?

When the soil dries to a point where the roots cannot extract water at the rate required by the plant

26

What is mottling?

The switching between saturated and aerated conditions gives rise to mottling, a speckled pattern of orange or rusty colored flecks

27

What is porosity?

The fraction of the soil volume that consists of holes

28

Why do coarse-textured soils have smaller total pore volumes but good drainage?

Coarse-textured have more macropores than fine-textured soils, however, fine-textured soils have many micropores which means they have a larger surface area of pores and therefore a larger total pore volume. Coarse-textured soils have more macropores meaning they have better drainage

29

Explain why it is harder to work a clay soil than sandy soil?

Because clay soils are more likely to become waterlogged which makes them very hard to cultivate

30

What is the phase lag of soil temperatures?

Energy is absorbed by the soil more while moving down the profile and the difference between the max and min temperatures will be smaller at depth. This delay in
reaching max and mins is the phase lag