Plant nutrition & the root environment Flashcards
1
Q
Why is soil so precious?
A
It is the outer layer of the earth’s crust where plants grow. The function of soil is to provide anchorage for plant roots, nutrients, water and allow gaseous exchange.
2
Q
Describe what 4 things soil is made up of?
A
Highly complex and dynamic material.
Made up of
1. minute particles of weathered rocks (minerals).
2. organic matter (living, dead and decayed)
3. air in the spaces between the soil particles
4. water in the gaps between the soil particles.
3
Q
How is rock broken up?
A
By various weathering processes into sand, silt or clay.
4
Q
How is Organic matter broken up?
A
By the activity of other living creatures and by micro organisms.
5
Q
What are the 3 types of rock called?
A
Sedimentary
Igneous
Metamorphic
6
Q
Why do soils vary in colour and consistency?
A
Soils vary in colour and consistency depending on the type of rock they derive from and the relative amounts of rock and organic matter they contain.
7
Q
What is sedimentary rock?
A
Formed by the deposition of material over time (sediment)
Sedimentary rocks are formed from the broken remains of other rocks that become joined together.
Examples of sedimentary rocks are limestone, chalk & sandstone.
Sedimentary rocks are the most vulnerable to weathering.
They often form sandy soils which are deep, easy to cultivate and can be infertile.
8
Q
What is igneous rock?
A
Igneous rocks are formed from molten rock that has cooled and solidified.
Eg. Granite and Basalt
Less susceptible to weathering.
9
Q
What is metamorphic rock?
A
Made by the transformation of existing rock types. Eg. Sedimentary or Igneous. through immense pressure or heat.
Eg. Slate, marble and quartzite.
More resistant to weathering that original rock.
10
Q
What is the parent rock?
A
Found in the lower horizons (the bedrock layer) and it determines what kind of soils you have.
11
Q
What is weathering?
A
The breakdown of rocks and minerals into smaller pieces to form soils.
12
Q
What is erosion?
A
The removal of rock pieces from the site of weathering. Should not be confused with weathering.
13
Q
What are the 3 types of weathering?
A
Physical
Chemical
Biological
14
Q
What does physical weathering mean?
A
The physical size of rock/fragments change, but there is no chemical change.
15
Q
Give 4 examples of physical weathering?
A
- Freeze/thaw action.
Water seeps into cracks in rocks and freezes & thaw action over time widens the gaps until they eventually shatter and break into smaller fragments. - Changes in soil temperature
Especially in very hot places. The sun baked the soil. Expansion and contraction of the soil surface occurs. - Physical abrasion
Of the rock surface. Wind or water can cause rock surfaces to rub together. Sand or Sea. - Cycles of wetting & drying.
Also cause soil to be worn down into smaller particles.
16
Q
Describe chemical weathering?
A
Chemical weathering DOES involve a chemical change. Rock structure is weakened and broken up by a chemical reaction. Sedimentary rocks such as limestone are more vulnerable to this type of weathering.
17
Q
3 Examples of chemical weathering?
A
- Rain water is naturally acidic as it reacts with carbon dioxide to form carbonic acid. This weak acid reacts with rock minerals to break them down and has a greater effect on ‘soft rocks’ like limestone. Eg. Malham Cove is made of limestone!
- Acid rain was more of a problem during the industrial revolution. when sulphur was released into the atmosphere by burning coal and fossil fuels. Eradicated in UK when clean air act legislation put in place. But still a problem in places like India, China & Japan. Sulphur emissions react with rain water to form sulphuric acid (a stronger acid than carbonic acid), and has the same effect but to a greater degree.
- Oxidation is the reaction of rock minerals with oxygen, thus changing the mineral composition of the rock. When minerals in rock oxidize they become less resistant to weathering. Iron, a commonly known mineral becomes red or rust coloured when oxidized.
18
Q
What is biological weathering?
A
Biological weathering is the breaking down of rocks by plants, animals and microbes. Living organisms.
19
Q
Give 3 examples of biological weathering?
A
Plant roots - especially trees, will force their way through cracks in rocks and open them up. Seeds fall into crevices and germinate, creating pressure in cracks and opening them up.
Microbes such as fungi, algae, lichens & bacteria will invade the surface of the rocks releasing chemicals to break them down so they can obtain mineral nutrients.
Burrowing animals will move rock fragments to the surface. Human activity also weathers rocks. These activities include mining, road construction, and housing developments.
20
Q
What 6 things affects weathering and soil formation?
A
Climate Organisms Landscape topography Parent material Time Man
21
Q
Is weathering faster when temperatures are hot or cold?
A
Weathering is faster when temperatures are higher generally and are extreme at upper and lower end. (freeze and thaw) And when water levels are high.
22
Q
Which type of rocks are most easily affected by weathering?
A
When rocks are more porous - eg.sandstone and limestone.
23
Q
What is a soil profile?
A
A soil profile is a vertical section through the soil which shows the layers (horizons). Usually to 1m deep.
24
Q
What are the four soil horizons called?
A
O Horizon - the top surface litter or organic layer.
A Horizon - the top soil.
B Horizon - the subsoil
C Horizon - Parent rock or bedrock
25
What is the O Horizon?
O Horizon - top layer or organic layer which contains fungi, animal and plant remains.
26
What is the A Horizon?
The top soil. Seeds germinate and plant roots grow in this dark coloured layer. It is made up of humus (decomposed organic matter) mixed with mineral particles.
27
What is the B Horizon?
The layer called the subsoil. It contains mainly mineral particles and less organic matter and is usually lighter in colour compared to top soil. Paler colour can be due to clay particles being washed downwards or mineral deposits which have drained from the layer above such as iron oxide which has a red/orange colour. As well as less organic matter.
28
What is the C Horizon?
The layer called the parent rock or the bedrock.
This is where the soil originates from and is broken down by weathering. This layer determines your soil type. (texture)
29
What factors can determine soil colour?
Mineral matter - what kind of parent rock - chalky white!
Organic matter content (darker)
Iron content an dhow much oxygen available gives a red rusty colour.
Moisture levels.
30
Compare Topsoil and Subsoil.
| What are they both composed of?
Topsoil - Composed of humus and mineral particles
| Subsoil - Composed mainly mineral particles.
31
Compare Topsoil and Subsoil.
| Where are they positioned?
Topsoil - uppermost layer
| Subsoil - layer below topsoil
32
Depth of topsoil and subsoil?
Topsoil - 5-40cm
| Subsoil - 30-100cm
33
Colour of topsoil and subsoil?
Topsoil - Darker due to OM content. Warms up quicker when darker.
Subsoil - Paler due to lack of OM and fine clay particles have been washed downwards or iron compounds.
34
Pore space and aeration of topsoil vs subsoil?
Topsoil is well aerated and varied pore space to give better water retention.
Subsoil compacted and very few pore spaces/poor aeration.
35
Difference in soil organisms in topsoil/subsoil?
Topsoil - rich environment for microorganisms, insects and worms.
Subsoil little or no soil organisms.
36
Difference between water content of top soil and sub soil?
Topsoil - good water holding capacity if well managed. Improved with OM content.
Subsoil may be waterlogged or dry depending on drainage. Usually drains slower as more consolidated.
37
Fertility of topsoil versus subsoil?
Topsoil -very fertile
| Subsoil - less fertile. Minerals washed into this layer from above are often in an unusable form for plants to absorb.
38
Cultivation differences between topsoil and subsoil?
Topsoil - cultivated
| Subsoil - Not normally cultivated.
39
Workability of topsoil versus subsoil?
Topsoil easier to handle.
| Subsoil Sticky/hard to handle.
40
Weeds in the top soil versus subsoil?
Top soil lots of weeds
| Subsoil No weed seeds
41
Difference between roots in top soil and sub soil?
Top soil - many plants have roots in this zone. Most suitable for plant growth.
Sub soil - Roots can extend into this zone for water and minerals. Much less suitable for plant growth.
42
Suitability for plant growth top soil versus sub soil?
Topsoil is most suitable due to optimum water, air, minerals, open structure, OM levels.
Subsoil can be penetrated by roots but has little or no OM for nutrition. Plays an important role in vigour of long term planting as influences how water moves through the topsoil and provides water reservoir and nutrients to deep roots.
43
What is humus?
Decayed plant and animal remains to the point where they don't resemble the original matter anymore.
44
Why is OM important?
For soil fertility, stability and formation.
45
What is humification?
The breakdown of course OM into humus
46
What 2 things can OM exist as?
```
Coarse OM (undecomposed)
Humus (decomposed)
```
47
What colour is Humus and what can it do?
It's dark in colour so it enables soil to warm up quicker.
48
Define soil texture? TYPE
The relative proportions of sand, silt and clay
It is determined by the feel of the soil.
Gritty - sandy
Soapy - silty
Smooth & sticky - clay
Soil TYPE cannot be changed easily as it is determined by the bedrock.
49
Define soil structure?
The arrangement of the mineral particles and organic particles into aggregates. It is the way the individual particles clump together.
Soil structure is determined by the texture plus the OM, plus the amount of water in the soil.
50
How can soil structure be changed?
By adding OM, green manure, cultivation, adding grit or sand, planting, mulching. It is structure which the gardener is always seeking to change.
51
What are the 3 different sized particles in the mineral part of the soil called?
Sand, Silt & Clay
52
Where all 3 particles are present in the soil what do we call it?
A loam. Pure loam contains all 3 particles in equal measures.
53
Describe characteristics in a sandy soil?
Gritty texture
Crunches when held close to the ear and rubbed together.
Inert - doesn't hold onto nutrients.
Free draining.
Coarse sand has poor water holding capacity.
Fine sand holds onto water better.
54
Describe characteristics in a silt soil?
Silt has a silky soapy feeling when wet and feels like flour when dry.
Generally inert but sometimes has the properties of clay. Generally behaves like a fine sand.
Silt has a good water holding capacity and plants can access the water.
55
Describe the characteristics of Clay soil?
Clay has a smooth sticky texture when wet and can be very hard when dry.
Clay particles are plate like in shape and stack in layers they are tiny.
Clay soils are fertile and hold onto nutrients.
They carry a negative charge which means they are attracted to and can bind with positively charged mineral ions eg. potassium, ammonium and magnesium. Called cation exchange capacity.
This is also why they hold onto water.
56
What are the 3 different ways to determine soil texture?
1. Hand texturing following a flow diagram.
2. Laboratory assessment of the relative proportions of sand, silt & clay by weighing and filtering through various sieves and using soil texture triangle.
3. Laboratory assessment of the relative proportions of sand, silt & clay by sedimentation and then use the soil texture triangle.
57
Characteristics of Sandy loam?
Feels gritty
Nutrients easily lost especially if coarse. Becomes acid. Described as hungry.
Water retention poor if coarse sand, marginally better if fine sand. But still poor compared to silt and clay.
Temperature is quick to warm up but also vulnerable to frosts.
Workability is easy.
58
Characteristics of a Silty loam?
Feels Silky/soapy when wet. Flour like when dry.
Good nutrient retention.
Good water holding capacity but when very wet weak structure, and easily damaged when walked on.
Drains well under normal conditions.
Slower to warm up than sandy soil.
Workability can be difficult as doesn't form crumbs easily.
59
Characteristics of a clay loam?
Feels sticky and smooth when wet. Hard when dry.
Good nutrient retention as a result of negative charge on clay particles. Cation exchange capacity.
Water holding capacity good. Slow draining.
In winter structure can be damaged due to water retention and compaction. Easily smeared when wet.
Slow to warm up due to colour and water content.
Heavy to work and compacts easily.
60
What are the benefits to plant growth if you add OM?
Affects soil structure. Opens pore space in heavy clay soils for air and water. When fully decomposed holds onto nutrients making them available to plant roots.
Will retain moisture in sandy soils.
Encourage earthworm activity which creates channels (air space) in the soil and nutrients to plants as worm breaks down OM.
61
What are the benefits of Soil Organisms to plant growth
Worms make channels through the soil to help drainage and aeration.
Mycorrhizae enables plant to absorb more water in 95% of plants it is thought.
Nitrogen fixing baceria in peas and beans make nitrogen available to plant roots.
Many many other soil organisms.
62
What are the benefits of soil mineral nutrients to plant growth?
Required for growth.
Soil parent material has a direct influence on the nutrient element contents of the soil.
Eg. Limestone parent rock supplies lots of calcium.
63
What are the benefits of water to plant growth?
Soil water is absorbed by plant roots and taken around the plant.
Helps to keep plant cells turgid, and therefore upright.
Key ingredient for photosynthesis.
Processes in cells require water.
Lack of water and plant closes it's stomata, photosynthesis stops and wilting occurs. Over prolonged periods of time death follows.
64
What are the benefits of soil air to plant growth?
Oxygen in the soil air allows aerobic respiration in the meristems of the root as they divide and grow. If the structure is open they can penetrate more easily. When soil is saturated with water (ie. no air pockets) anaerobic respiration occurs and toxic ethanol builds up leading to root death.
65
Describe soil structure?
The arrangement of soil particles in the soil and how they group together as aggregates or crumbs.
Soil structure is an arrangement of soil particles plus air, water and organic matter.
Soil structure is defined by the way the individual particles of sand, silt and clay clump together.
This in turn determines the size of pore spaces in between these groups of particles. So crumb structure links to water holding capacity.
Mycorrhizae, earthworms, soil micro organisms and plant roots help create aggregates by 'sticking them together'. This is why organic growers are so keen on adding organic matter and feeding the soil not the plant.
66
What is a well structured soil with a crumbly structure called?
Friable
67
What does friable mean?
A well structured soil with a crumbly structure.
It means easily broken up.
A very wet clay soil is not friable.
68
Which type of soil has the largest particle sizes?
Sand
| Therefore more air around the particles, so can dry out quicker.
69
Which type of soil has the smallest particle sizes?
Clay
Pores are too small and not enough air around the plant roots.
Excess water does not drain freely.
70
What happens to the crumb size as you progress through the soil horizons?
Smaller at the surface gradually increasing as you travel downwards towards the parent rock.
71
Give 2 examples of poor soil structure?
Sandy soil which has been over cultivated with no OM added will be fine and dusty.
Rock particles are single grains which are not stuck together. Prevents contact between roots and soil.
Very porous means leeching of nutrients.
Very fine so erosion occurs by wind and water.
Clay soil can become compacted if walked on or heavy machinery moving over it.
Sometimes a compacted clay pan forms in the A horizon preventing drainage so you'll see surface pooling.
72
What is surface capping?
Surface capping or a surface pan is where a crust forms at the surface which prevents seeds germinating or prevents water draining downwards.
Occurs in exposed soils after prolonged rain, especially sandy and silty soils.
Constantly hoeing the surface can also contribute.
Can also lead to surface run off or erosion.
73
What 4 things must soil be for plants to grow well?
1. Allow gas exchange. (ie. not continually saturated with water).
2. Hold water that is available to roots.
3. Hold nutrients that is available to roots.
4. Enable good anchorage.
74
How can structure be destroyed?
1. Cultivation
Soil can be overworked eg. raking to dust!
Cultivation timing - eg. clay soil cultivated he wet can lead to compaction and formation of soil pans.
2. Heavy rainfall/irrigation can destroy soil surface on fine grained soil. Surface Capping.
3. Compaction by footfall/machinery.
4. Removal of vegetation leaving soil exposed. (veg garden).
5. Monoculture on a large scale.
75
How can crumb structure be improved?
1. Freezing/thawing good for improving clay soils.
2. Root growth - roots grow into cracks and keep them open. When they die off they leave drainage channels.
3. Soil organisms - eg earth worms create drainage channels and add OM.
4. Cultivation - eg. digging/forking clay.
5. Allowing organic matter - eg leaf litter or adding compost regularly will improve sandy single grain soils or help to break clay clods into smaller aggregates.
6. Drainage systems will help over wet soils become more workable.
7. Adding lime to clay soils in Autumn helps to break down the clods into smaller aggregates.
8. Mulching the surface of the soil to prevent capping.
9. Sow a green manure.
76
What is a soil pan?
Soil pans are impermeable layers in the soil profile which restrict water infiltration and drainage and oxygen availability and restrict root growth.
77
What is surface capping?
A layer of compacted soil particles form at the soil surface. May restrict water and air movement, and stop seedling emergence. Due to water pounding bare soil in winter and damaging the soil structure.
78
What is an iron pan?
Light sandy soils are prone to forming an iron pan in the sub soil as the iron particles which have leeched downwards collect to form a hard impermeable layer. Water cannot drain through this layer, and so soil above can become waterlogged.
79
What is a compaction pan?
Clay soils can form a pan in the top soil due to surface compaction such as heavy machinery or repeated foot traffic.
80
What is a cultivation pan?
A compaction pan that restricts root growth, aeration and drainage due to cultivating the (Clay) soil repeatedly to the same depth and smearing a clay soil. Compacted soil layers means that air is not available for root growth and drainage may be impeded. Can be caused by rotavators or hand tools.
81
Name 4 different types of Soil pans?
1. Surface capping
2. Iron pan
3. Compaction pan.
4. Cultivation pan.
82
Which soil pans are in the A horizon?
Surface capping
Cultivation pan
Compaction pan.
83
Which soils are in the B horizon?
Iron pan.
84
What is the effect on soil pans on plant growth?
Reduced root penetration.
Less anchorage.
J shaped carrots
Shallow rooting if the upper layer is saturated causing poor anchorage and stunted growth..
Waterlogging can occur above pans which cause root death when oxygen is not present.
In compacted clay plans may be enough air space - so not enough oxygen available for root cell respiration.
85
What to do if you've got surface capping?
```
Incorporate OM
Mulch with OM.
Don't over cultivate.
Plant green manure.
Break up surface with a hoe to assist water penetration or seedling emergence, careful not to over cultivate.
```
86
What to do if you have an iron pan?
Deep cultivation with a tractor mounted device or double digging.
87
What to do if you have a soil cultivation pan in clay soil?
```
Timing is important. Not when wet.
Do not keep cultivating to same depth.
Add organic matter. Add grit sand.
Double digging.
Large scale use a subsoiler which is tractor mounted.
```
88
What can we do if we have a compaction pan in a clay soil? (lawn or border)
Hollow tine aeration to relieve compaction in lawn.
| Double dig and add organic matter in a border.
89
What is cultivation for?
Cultivation is used to break up large clods, break up pans and to create a fine tilth. (crumb structure) suitable for planting or sowing seeds.
90
What is primary cultivation?
First digging to be carried out.
Usually to depth of 15-60cm (dependant on depth of topsoil.)
Allows additions to be made such as materials to improve drainage or water retention.
Digging, double digging and rotavating.
Soil left as large clods.
91
What 4 things does cultivation do?
1. Improves soil structure by alleviating compaction an developing crumb structure.
2. Brings air into the soil and improves drainage.
3. Provides a chance to apply fertiliser. Manure/OM/Lime.
4. Allows residue to be buried. eg. annual weeds/crop residue.
92
What is the negative about soil cutivation?
Disturbs natural soil biology.
Leads to soil moisture loss by exposing further surface area to the open air.
Especially important on sandy soils in hot weather.
93
What is the ultimate soil everyone is aiming for?
Free draining but moisture retentive!
94
When and how to cultivate a clay soil?
```
Autumn.
When not wet.
Autumn digging allows frost to break up the soil over winter thus help improve the structure.
Frost will break down large clods.
Add OM in Autumn.
```
95
When and how to cultivate a sandy soil?
OM added in spring. Otherwise nutrients will be leeched away over winter if added in autumn.
Add a mulch in autumn of OM as this will prevent surface capping.
Green manure also beneficial to sandy soils.
96
Describe single digging?
The use of a spade to dig a 30cm trench.
1 spit or 1 spades depth.
Place soil to the opposite end of the area to be dug.
A second trench is made behind the first. The soil from this second trench is inverted back into the first trench burying annual weeds.
Digging continues methodically with each trench being inverted into the preceding until the final trench is filled in with the soil from the first trench.
Working backwards means that the newly dug soil is not walked on.
97
Describe double digging?
Same as single digging, but bottom of trench is forked over and OM is added!
98
What is a rotavator used for?
```
Primary and secondary cultivation. depending on depths of blades.
Good for large areas.
Not good for raised beds.
Fine tilth for seed sowing. (secondary)
Breaking up a soil cap. (secondary)
Incorporating green manure. (primary)
Controlling annual weeds. (primary)
Incorporating fertilser. (primary)
Breaking up a compacted pan. (primary)
```
99
What does primary cultivation include?
Digging, double digging and rotivating.
Allows additions to be made such as OM to improve nutrients and soil structure/drainage.
Soil is left as large clods.
100
What does secondary cultivation include?
Top 5-15cm of soil is worked to create a suitable tilth and a level surface.
A good crumb structure suitable for planting or sowing seed.
Cultivation depth is shallow.
Main body of soil left undisturbed.
Fork, hoe, rake, rotavator.
101
What are the steps for secondary cultivation?
1. Fork over surface to break up large clods further.
2. Consolidate.
3. Rake in all directions removing stones as exposed.
4. Consolidate.
5. Rake surface to create a fine tilth which is level.
102
Describe consolidation?
The treading of soil that has been forked over and raked. Using heels of the feet. Zorba the greek!
Consolidation breaks down soil clods and removes large air pockets so soil does not become uneven over time as it settles.
The seed bed will remain level.
This facilitates good contact between plant roots and soil particles.
103
What are 5 characteristics of a seed bed?
1. Even and level surface.
2. Weed free.
3. Uniform firmness.
4. Adequate soil moisture.
5 Worked to a depth of 15cm with fine tilth for small/medium seeds.
104
6 named methods of cultivation?
1. Single digging. (primary)
2. Double digging (primary)
3. Rotary cultivation (primary and secondary)
4. Hoeing (secondary)
5. Consolidation (secondary)
6. Tilth production by raking (secondary cultivation)
105
What are the best timings for cultivating a clay soil?
Autumn - primary cultivation.
Dig over into large clods and add OM.
Not when too wet.
Leave for frost to break down over winter.
Secondary cultivation in March /April when soil is not waterlogged.
106
What are the best timings to cultivate a sandy/fine soil?
Mulch surface with OM in Autumn or plant green manure.
Feb/March - Primary cultivation. Add OM.
March - secondary cultivation.
Dig as little as possible April onwards to avoid drying out.
107
What is the no dig method?
No dig is where organic mulches are added to the surface of the soil and the soil organisms (worms) incorporate it into the soil.
Cardboard used as layers initially to supress weeds.
Often used with bed system for growing veg.
108
Give 6 benefits of No Dig Method?
1. Beneficial soil organisms are not disturbed.
2. Soil structure is improved and maintained and not damaged. Earth worms do the mixing.
3. Fungal strands of mycorrhizae are not broken by digging.
These fungi help plants to absorb nutrients.
If mulches do not contain weed seeds, weed seed from the top soil is not brought to the surface to germinate and cause weed problems.
4. Better if you have physical limitations.
5. Increases worm population.
6. Higher yield for less work.
109
Give 6 limitations of the No Dig Method?
1. Organic matter added may contain weed seed unless it's hot composted.
2. Pests not brought to surface for predators to deal with. Slug eggs. Worms for birds.
3. May be difficult to sow fine seeds as the structure may not be fine enough for seed bed.
4. Need A LOT of organic matter to add to the layers.
5. If fresh OM is added it will take a long time to decompose.
6. Initial cultivation may be needed if pans exist or its a solid clay type. May take a long time for soil to improve.
110
Describe the 'bed system' of growing fruit and vegetables?
Growing crops in permanent beds which may be at ground level or raised with a permanent pathway around them. Dimensions are important to enable working on the beds from the path without standing on the soil.
111
What is the maximum width of a raised bed and why?
1.5metres.
| So that you can reach to the centre without having to stand on the bed.
112
What is the maximum length of a raised bed and why?
3 metres.
| So that you can walk around the bed easily.
113
How wide should a pathway be between raised beds?
0.5metres.
Wide enough for a wheelbarrow.
1 metre if needed for wheelchair access.
114
What can pathways be made of between raised beds?
Woodchip, bark, gravel, trodden earth, turfed or weed proof membrane.
115
Benefits of a raised bed system?
Plants can be more closely planted which in turn reduces weed problems as they knit together and create more shadow.
Soil warms quicker because it can be raised.
Easier to manage a crop rotation system as you can see clearly where each growing area is.
Drains better as the soil level can be raised.
Only bed area cultivated so less work.
Deeper soil for root growth.
Suits a no dig system.
Fertiliser, mulches and weed killer use is targeted only on beds not paths. Less waste.
More working days as less winter wet cloggy soil.
Can fill beds with required soil type for specific crop.
Access for disabled gardeners as can work from a wheelchair if bed is raised.
116
Limitations of a raised bed system?
More efforts to establish initially.
Costly if edging used.
May require additional maintenance of wooden edge stripping for examples.
Soil may dry out too quickly in raised beds and plants may wilt with lack of water.
Imported top soil for raised beds may have the wrong texture for the crops. May have perennial weed seed. Also additional cost.
If raised beds are tall primary cultivation is tricky as you have to climb on the top of the beds so you can use the digging fork so there is a risk of falling.
OM should be added regularly so digging is required.
Rotavator is difficult to use.
