Topic 8: Soil Fertility

Question 1

What is soil fertility?

Answer 1

Soil fertility is the ability of soil to sustain plant growth

Question 2

What are the features of fertile soil? (9)

Answer 2

Water content
Soluble materials
Air content
Dead organic matter
PH
Soil biota
Soil texture
Soil structure
Soil depth

Question 3

Why is the water content important in fertile soil?

Answer 3

A fertile soil allows good drainage- doesnt get waterlogged, but retains enough from the survival of soil biota
Nutrients needeed by plants are absorbed in the ionic form that are dissolved in water

Question 4

What macronutrients do fertile soils contain?

Answer 4

Nitrogen
Phosphorous
Potassium
Present in ionic form: nitrates,phosphates,potassium ions

Question 5

What micronutrients are found in fertile soils?

Answer 5

Boron
Cobalt
Copper
Iron
Manganese
Magnesium

Question 6

Why are soluble materials important in fertile soils?

Answer 6

Toxic ions (e.g. aluminium and heavy metas) are absorbed onto the surface of mineral particles (usually clay) s they cannot dissolve in water where they could harm soil organisms

Question 7

Why is the air content important in fertile soils?

Answer 7

Most living organisms in soil & many processes that increase fertility are aerobic
So well aerated soils are likely to be more fertile

Question 8

Why is dead organic matter an important feature of fertile soils?

Answer 8

Fertile soils have a high dead organic matter content
It releases plant nutrients as it decomposes
It increases water retention and provides food for soil biota

Question 9

Why is the PH relevant to a fertile soil?

Answer 9

Has to be in the range of tolerance for plants & soil biota
Acidic soils can increase leaching of plant nutrients & damage root cell membranes
In alkaline conditions, phosphates are insoluble

Question 10

What is the PH of a fertile soil?

Answer 10

Between 5.5 and 7.0

Question 11

What are the 5 important examples of soil biota?

Answer 11

Detrivores
Decomposers
Nitrogen-fixing bacteria
Nitrifying bacteria
Mycorrhizal fungi

Question 12

Examples of detrivores and why they are important in fertile soils

Answer 12

They break up dead organic matter, release nutrients into the soil, increase soil drainage and aeration by tunnelling
E.g. worms. Beetle larvae, millipedes,wood lice,slugs

Question 13

Examples of decomposers and their importance to fertile soils

Answer 13

E.g. bacteria and fungi
They break down dead organic matter
They secrete digestive enzymes
Rely on detrivores to physically break up dead organic matter and increase its surface area

Question 14

What is the role of nitrogen fixing bacteria?

Answer 14

Convert gaseous nitrogen to ammonium ions

Question 15

What is the role of nitrifying bacteria?

Answer 15

Oxidises ammonium ions to nitrite ions, then nitrate ions

Question 16

What is the role of Mycorrhizal fungi and why are they important in soil biota?

Answer 16

They form symbiotic relationships with plant roots and aid phosphate uptake by plants

Question 17

What controls the sol texture?

Answer 17

The proportions of different size categories of mineral particles present in the soil

Question 18

What is the diameter range of clay?

Answer 18

Less than 0.002

Question 19

What is the diameter range of silt?

Answer 19

0.002-0.02mm

Question 20

What is the diameter range of sand?

Answer 20

0.02-2.0 mm

Question 21

Compare the drainage rate of sandy and clay soils

Answer 21

Better drainage in sandy soils- poor in clay
Because of the large pore spaces in sandy soil, so rapid drainage, allowing more aeration but less water content

Question 22

Compare the capillary action of sandy and clay soils

Answer 22

Tiny pore spaces between clay particles allow water underground to rise towards the surface
No capillary rise in sandy soils

Question 23

Compare aeration in sandy soils and clay soils

Answer 23

Pore spaces are filled with air in well-drained sandy soil
Clay soils are more likely to be waterlogged with a low aeration rate

Question 24

Compare nutrient retention in sandy and clay soils

Answer 24

Nutrients ions absorb easily onto clay particles but not onto sand particles

Question 25

Compare the thermal capacity of clay and sandy soils

Answer 25

High termal capacity in clay soils because of high water content- warm up and cool slowly Sandy soils have low thermal capacities, warm up rapidly after cold weather

Question 26

Compare the root penetration of sandy and clay soils

Answer 26

Root penetration is easier in sandy soils because of the capillary water that holds together clay particles- it is harder for plant roots to penetrate that

Question 27

Compare the ease of cultivation of sandy and clay soils

Answer 27

The lack of adhesion between particles in sandy soils makes it easier to cultivate than clay soils

Question 28

Loam soils ae the most ideal for cultivating most crops. Why?

Answer 28

They have an even mix of sand,silt and clay (40;40;20) Ideal properties: good drainage, water retention, high nutrients content

Question 29

Explain the structure of soil

Answer 29

Soil particles form aggregates called peds The particles are bound together by polysaccharide gums produced by decomposition, by fungal hyphae, by roots, by soil biota and by hydroscopic clay particles The ped type affects the soil properties and fertility

Question 30

What are the types of peds?

Answer 30

Crumb peds Platy peds

Question 31

Crumb peds

Answer 31

Small and round They produce good drainage,aeration, easy root penetration and so improve soil fertility

Question 32

Platy peds

Answer 32

Large and flat Reduce drainage, aeration and root penetration Produce less fertile soils

Question 33

How does soil depth affect the fertility?

Answer 33

Deeper soils are less likely to become waterlogged and dry out rapidly They can aid good root anchorage

Question 34

How can human activities affect soil fertility by affecting aeration?

Answer 34

By ploughing and drainage It makes the soil more aerobic, which increases rate of : Nitrogen fixation Nitrification Decomposition of dead organic matter

Question 35

How do human activities increase soil nutrient levels?

Answer 35

By adding inorganic fertilisers or organic matter By supporting natural processes that increase nutrient levels e.g. bacterial nitrogen fixation

Question 36

How can farmers deplete soil nutrient levels?

Answer 36

Soil erosion Biomass removal Inhibiting natural processes that increase nutrient levels Increasing leaching of dissolved nutrients

Question 37

How can irrigation, a human activity, affect soil fertility?

Answer 37

It increases fertility in areas where water is a limiting factor on growth It can also dissolve nutrients so more can be absorbed by plants in ionic form

Question 38

How can soil compaction by human activities affect soil fertility?

Answer 38

Excessive use of machinery or high livestock density can compact soil Reduces aeration, increases chances of water logging

Question 39

How can ph control by humans affect soil fertility?

Answer 39

It can ensure nutrients are soluble but not too easily leached