Lecture 4 - tillage

Question 1

5 things soil provides plants with?

Answer 1

• Support
• Nutrients
• Water
• Oxygen requirements of roots (except wetland plants)
• Protection of underground buds from temp. extremes

Question 2

5 reasons why soil can be a potentially hostile environment?

Answer 2

• Pathogens
• Root grazers
• Toxins
• Too much or too little water
• Inadequate aeration

Question 3

why is soil potentially one of the most complex substances to study?

Answer 3

• Has a 3-phase system:
• Solid (mineral, organic)
• Liquid (free water, Structural / unavailable water)
• Gas (air) (enriched in CO2, depleted in O2)

Question 4

what is half of the volume of soil?

Answer 4

pore space containing air or water

Question 5

describe soil air

Answer 5

is distinct from atmosphere and varies with depth due to processes, microbes and root and microbial respiration

Question 6

4 reasons soils are tilled?

Answer 6

• Prepare a fine loose soil layer for seedlings to establish.
• Bury weeds, crop residues and pathogens.
• Release nutrients.
• Reduce surface and subsurface compaction

Question 7

what are 3 conventional tillage methods?

Answer 7

1. Inversion tillage (mouldboard plough)
2. Disking / power harrow,
3. Seed (drill)

Question 8

what does conventional tillage involve?

Answer 8

the use of lots of machinery

Question 9

2 minimum tillage techniques

Answer 9

1. Shallow disc cultivation,

2. Drill inserts seed (plus fertilizer) (and chemical weed kill)

Question 10

how do minimum tillage techniques work

Answer 10

lighter machinery

often leaves a lot of crop residue on the surface which helps to bind the soil together

Question 11

what is a zero tillage technique?

Answer 11

1. Slot drill adding seed and fertilizer (and chemical weed kill - still not good)- almost complete cover by crop residue
   - now alot more common

Question 12

how does zero tillage work?

Answer 12

direct drill, lighter machinery again

Question 13

what is the advantage of zero tillage?

Answer 13

• Soil organisms are left largely undisturbed - helps to maintain soil quality in ways that normal ploughing doesn’t
• consequences = reduced erosion

Question 14

what is the big issue with tillage?

Answer 14

compaction

Question 15

What is an issue with compaction?

Answer 15

• Compaction can be so tight roots and water can’t get through - restricting roots to shallow part of soil and therefore in a drought the roots can’t reach low level water

Question 16

how do farmers try to reduce compaction?

Answer 16

increased width of machinery and wheels to spread weight

Question 17

what are the problems caused by conventional tillage?

Answer 17

loss of organic matter, nutrients, and water storage, increases soil erosion, and damages beneficial fungal symbionts reducing nutrient use efficiency, and reduces earthworm populations involved in aggregation and soil drainage

Question 18

despite the bad effects of tillage why do farmers continue to do it?

Answer 18

short term consequences are often better

Question 19

4 physical properties of soil

Answer 19

1)particle size distribution
relative proportions of gravel, sand, silt, clay
2) Structure - how particles are organized into aggregates
3) Water-holding capacity – controlled by porosity, structure and texture
4) Aeration – controlled by water-holding capacity

Question 20

what is soil texture classified by?

Answer 20

Based on particle size distribution of mineral fragments in soil - how much silt, clay and sand

Question 21

what soil water availability depend on?

Answer 21

the soil property; texture

Question 22

describe the stability of soil texture

Answer 22

Soil texture is very stable - only changes slowly due to weathering which
affects major soil properties

Question 23

describe a clay soil

Answer 23

Clay soils can store large amounts of water and nutrients but drain slowly and are prone to waterlogging

Question 24

describe a sandy soil

Answer 24

Sandy soils drain very quickly and store little water or nutrients but provide good aeration to roots

Question 25

describe a loam soil

Answer 25

Loam soils- in which there is a mixture of sand, silt and clay- are optimal for most plants.

Question 26

what defines soil structure

Answer 26

How particles are aggregated and organized together into peds - these are discrete units separated by voids and natural planes of weakness

Question 27

why is soil structure important

Answer 27

because it controls the passage of water and oxygen into the soil and affects nutrient-holding capacity

• Structure can overcome some of the limitations imposed by texture
• creates spaces roots can grow through -( Pores are found between and within peds)

Question 28

what plays a crucial role in structure?

Answer 28

organic matter

Question 29

what farming technique majorly impacts structure?

Answer 29

• tillage - causes poor drainage

Question 30

describe the importance of aggregate stability

Answer 30

• Aggregate stability- resistance to saturation with water is reduced by cultivation- particularly for largest aggregates

Question 31

explain the cascade caused by loss of organic matter

Answer 31

loss of organic matter(carbon) = loss of aggregation due to loss of macropores = reduced water infiltration = plants grow worse and high surface run off = soil erosion = loss of clays = cycles starts again

Question 32

how are peds formed? (7 ways)

Answer 32

1) colloidal fraction
2) cementing agencies
3) expansion and contraction by wetting and drying
4) plant roots
5) micro-organisms
6) fauna e.g earthworms
7) cultivation and drainage - can improve structure but often causes loss of aggregates

Question 33

3 ecosystem engineers involved in formation of macroaggregates

Answer 33

1. Fine roots, especially of grasses
2. Mycorrhizal fungi and other fungi
3. Earthworms and other soil animals

Question 34

whats the issue with loss of macroaggregates?

Answer 34

• Can take decades to restore macroaggregates once they have been broken up

Question 35

After intense periods of cultivation how can macroaggregates and soil carbon be restored?

Answer 35

the use of grass (leys - e.g. grass and clover) - Leys have very positive effects on physical structures of soil

Question 36

describe the importance of soil organic carbon

Answer 36

• 1% increase in soil organic carbon increases water storage capacity by nearly 10%