Topic 11: Abiotic Factors And Their Control

Question 1

Why is it important to control abiotic factors in agriculture?

Answer 1

Every species has its own range of tolerance for every abiotic factor
By maintaining conditions in optimum range results in optimum productivity

Question 2

Abiotic factors controlled in agriculture

Answer 2

Temperature
Light
Water
Soil fertility
Aeration
Soil salinity
Soil ph
CO2
Topography
Wind

Question 3

Importance of suitable temperatures

Answer 3

Length of thermal growing season
Frost-free period
Impact on evaporation
Biochemical reactions
Thermoregulation

Question 4

Why is the length of the thermal growing season important?

Answer 4

Needs to be warm enough for growth, not just survival
Increased temp, increases photosynthesis, plants lose water faster

Question 5

Why is a frost-free period important?

Answer 5

Some crops are damaged by frost
E.g. maize
They are particularly damaging to flowering plants

Question 6

How does global worming affect the frost-free period?

Answer 6

Global warming means earlier flowering seasons
So plants are more vulnerable/exposed to frost

Question 7

Impact of temperature on evaporation?

Answer 7

Higher temps, higher evapotranspiration
This increases the crops water requirements

Question 8

Impact of temperature on biochemical reactions

Answer 8

Rate is increased by temperature
Including those involved in photosynthesis and plant growth

Question 9

Importance of thermoregulation

Answer 9

Mammals/bords use food energy to maintain constant internal body temperature
If it is cold, more energy than usual is used for temperature instead of for growth

Question 10

How can temperature be controlled?

Answer 10

The selection of fields can affect temperature- low lying areas are more likely to experience frost
Or southern facing slopes in the northern hemisphere will be warmer
Intensive methods e.g. greenhouses
Transparent plastic cloths can be placed over fields to help retain warm air close to the ground
Iivestock kept in shelters or heated buildings

Question 11

How is light important in agriculture/

Answer 11

For photosynthesis

Question 12

explain the effects of variation in light intensity

Answer 12

Photoperiodism (daylength)- some plants require longer daylight periods for flowering
Daylength can also affect reproductive functions of livestock species

Question 13

How can light be controlled?

Answer 13

Artificial light used to extend growing season
The artificial production of autumn lighting conditions in spring-produce another mating season and lambing season in the autumn

Question 14

Importance of water

Answer 14

Physiological solvent
Nutrient absorption
Cell turgidity
To transport materials
To replace water lost in transpiration
Gaseous exchange-stomata

Question 15

Name a crop with a high water requirement

Answer 15

Most rice varieties

Question 16

Give a crop with a low water requirement

Answer 16

Wheat

Question 17

In what ways can water supply affect crops?

Answer 17

Amount available
Reliability
Quality

Question 18

How can the amount of water affect crops?

Answer 18

Plants are adapted to the amount available
They might have complex rot systems to increase SA in contact with water that contains nutrients
Might have longer roots in clay soil to reach water under clay

Question 19

How can the reliability of water affect crops?

Answer 19

Difficult for farmers to plan activities if they dont know about water availability
Particular issue in areas with unreliable seasonal rainfall
In reliable climates make it more difficult expensive to farm

Question 20

How can the quality of water supply affect crops?

Answer 20

If substances are dissolved in irrigation water it can be an issue
High salt content can cause salinisation which leads to osmotic dehydration

Question 21

What problems are caused by waterlogged soils?

Answer 21

Higher risk of fungal or infectious diseases
Soils become anaerobic-better for denitrifying bacteria, which reduces soil fertility as nitrates are lost

Question 22

What methods can be used to reduce soil water levels?

Answer 22

Excavation of drainage ditches or installation of drainage pipes
Deep ploughing
Avoidance of soil compaction by machinery or livestock
Provision of conditions to encourage worms-aeration

Question 23

Problems for crops caused by water shortages

Answer 23

Plants close stomata to prevent water loss, which prevents co2 absorption nd photosynthesis
Reduces crop productivity
Lack of water reduces cell turgidity and means there is no solvent for reactions

Question 24

Problems for livestock caused by water shortages

Answer 24

Increased trampling damage if have to walk longer distances for water
Increases risks of erosion and desertification
Livestock have to go on get distances-reduces body mass, kills more plants

Question 25

Methods to increase water availability

Answer 25

Crop irrigation
Soil mulching
Suitable conditions for worms
Reduce soil compaction
Add organic matter

Question 26

When must nutrients be added to soil?

Answer 26

When nutrients are removed in crop harvest or lost in natural processes
If the soil is deficient of that nutrient

Question 27

Primary macronutrients needed by plants

Answer 27

Nitrogen
Phosphorous
Potassium

Question 28

Secondary macro nutrients

Answer 28

Calcium magnesium sulfúreo

Question 29

How can nutrients be applied in agriculture?

Answer 29

Primary macronutrients- fertilisers
Secondary & micronutrients applied if soil if nutrient deficient or in intensive systems e.g. hydroponics

Question 30

What are organic fertilisers?

Answer 30

Animal or plant material that release nutrients as they decompose

Question 31

Advantages of organic fertilisers

Answer 31

Many are wast products
Locally available
Increase soil humus content
Increase soil biota

Question 32

Disadvantages of organic fertilisers

Answer 32

Nutrient composition cant be controlled
Nutrients released slowly
Bulky/high water content-expensive to transport
Usually cant be added to growing crops

Question 33

Advantages of inorganic fertilisers

Answer 33

Nutrient composition can be controlled to meet specific requirements
Nutrients are released rapidly

Question 34

Disadvantages of inorganic fertilisers

Answer 34

Require large amounts of energy to manufacture
Don’t add organic matter to soil-humus and biota decline
Toxic to worms
High solubility-leached

Question 35

What is hydroponics?

Answer 35

Involves the growth of crops in a nutrient solution rather than a solid growth medium
Usually in a greenhouse
Part of intensive system
Productivity is maximised

Question 36

Advantages of hydroponics

Answer 36

Optimal nutrient supply
All roots in contact with nutrient medium
No soil to hold pathogens
No weeds
No pollutants
Crops fresher for longer
More attractive to customers-no soil on them

Question 37

Disadvantages of hydroponics

Answer 37

Very expensive
Requires high energy and nutrient inputs
High levels of technical knowledge needed

Question 38

why is soil aeration needed?

Answer 38

Root respiration,nitrogen fixation,decomposition

Question 39

How is soil naturally compacted and aerated?

Answer 39

Naturally compacted by gravity
Tunniling of detrivores and roots

Question 40

How can aeration be controlled?

Answer 40

Ploughing
Adding organic matter
Low tillage methods
Trampling reduced

Question 41

How can soil salinity be controlled?

Answer 41

Avoiding farming practices that increase salinity e.g. irrigation using ground water with high salt content, because the salt stays in the soil when the water has evaporated

Question 42

Problems with low soil PH

Answer 42

Can increase leaching and inhibit nutrient uptake
Can mobilise toxic ions

Question 43

How can soil PH be increased?

Answer 43

Adding crushed lime

Question 44

How can PH be decreased in the soil?

Answer 44

Spreading powdered sulphur

Question 45

How can carbon dioxide be controlled?

Answer 45

Increased in greenhouses by burning carbon-based fuel e.g. paraffin
The increased cost may be justified by the higher market value of greenhouse corps

Question 46

How can wind velocity be controlled?

Answer 46

Windbreakers e.g. hedgerows or Trees