Soil PH, Fertiliser, Growing Media & Hydroponics Flashcards
1
Q
What is soil PH?
A
A term used to express the acidity or alkalinity of a soil solution and ranges from 4-8 for good plant growth.
It is measured on a scale of 1-14.
2
Q
What is the ideal PH for growing most plants?
A
6.5
3
Q
Why do soils become acid over time?
A
Because they leach calcium.
Sandy soils often more acidic because they leach calcium more readily.
4
Q
Where is acidic on the PH scale?
A
Below 7 (between 7-0)
5
Q
Where is alkaline on the PH Scale?
A
Above 7 (between 7-14)
6
Q
Where is neutral on the PH scale?
A
7
7
Q
What happens to plants if they are grown in soils outside of the 4-8 range on the PH scale?
A
Become nutrient deficient or toxic levels of nutrients build up.
8
Q
How does soil PH affect nutrients to plants?
A
If the soil solution is too acid or too alkaline the nutrients may not dissolve and therefore won’t be available for plant uptake.
9
Q
What PH do most nutrients dissolve at?
A
6.5
10
Q
Which nutrients are less available below a PH of 6?
A
Nitrogen, phosphorous and potassium are less available.
11
Q
Which minor nutrient is affected by alkaline soils?
A
Trace minerals and minor nutrients such as Iron. Which leads to lime induced chlorosis. Some plants very sensitive to iron deficiency. (Rhododendron).
12
Q
Which kind of soils are more favourable conditions for disease like club root?
A
Acidic soils.
13
Q
Which kind of soils are more favourable conditions for diseases like potato scab?
A
Alkaline soils.
14
Q
Does PH affect the amount of nutrients in the soil?
A
No, the nutrients are still present they are just not readily available to the plant if the PH is at either extreme.
15
Q
Give 3 examples of sources of acid that affect the soil?
A
- Carbonic acid in rain. (causes chemical weathering of rocks)
- Fertilisers - bacteria involved in nitrification of ammonia to nitrate produce H+ ions.
- Organic matter - humic acid from microbial decomposition of organic matter.
- Crop removal - calcium stored in the plants are removed each time they are harvested and therefore slowly reduce in the soil each season.
16
Q
Give 3 examples of how soils can become acid?
A
- Leaching of calcium from the soil. (particularly in sandy soils)
- Calcium removal from the soil by growing plants.
- Over application of ammonium fertilisers.
17
Q
What happens if you add Gypsum to clay soils in Autumn?
A
Free lime on clay soils can lead to better crumb formation by flocculating the clay.
18
Q
What is the name of the lime product added to clay soil to flocculate the soil and make it form a better structure?
A
Gypsum (Calcium sulphate)
19
Q
What 2 other things have an impact on the structure of the soil, that is related to PH?
A
- Earthworms are generally more active and effective when there is some free lime in the soil. They do not like very acidic conditions.
- Below certain acidity levels soil bacteria stop decomposing organic matter.
20
Q
Which is more difficult lowering or raising PH?
A
Lowering PH is expensive and difficult.
Raising PH is easier and cheaper.
21
Q
How do you lower the PH of soil?
A
Add an acidifying agent. Often sulphur.
Takes a long time, weeks. Months in winter.
22
Q
How do you raise the PH of soil?
A
Add garden lime. (calcium carbonate).
Easy and cheap to do.
23
Q
What is the main limitation with adding lime?
A
Over liming may affect availability of nutrients. Eg. lime induced chlorosis due to iron being unavailable.
24
Q
How do you add lime (calcium carbonate)?
A
Worked into top soil to 15 cm depth.
Apply in winter.
Has effect for 1-2 years.
25
What can you add to the soil to lower the PH? Make it more acidic.
Horticultural sulphur
| Ammonium sulphur.
26
How quickly does adding horticultural sulphur work?
Acidification takes weeks, maybe months if cold weather. Need to apply in warm weather.
Sulphur dust is quicker acting than sulphur chips & more expensive.
Can still take years to affect root zone.
27
What are the limitations when applying horticultural sulphur to lower the PH?
Acidifying soils high in calcium carbonate can be futile.
| Health & safety considerations when applying.
28
What does adding organic material - leaf mould, pine needle leaf, peat, or composted bracken or manure do to the PH?
Usually lowers PH. Acidifies.
Has an increased amount of humic acid.
Peat is the most effective as most acid.
Need to repeat frequently as OM is broken down.
29
What does calcifuge mean?
Lime hating plants.
| also called acid lovers.
30
What does calcicole mean?
Lime loving plants!
31
Give 4 examples of Calcifuge plants?
```
Lime hating plants. Acid lovers.
Rhododendron 'Christmas cheer'
Arbutus unedo
Camellia japonica
Acer japonicum
```
32
What are lime hating plants like Rhododendron 'Christmas cheer' and Camelia japonica most prone to?
Iron becomes less available as PH increases.
| These plants are particularly prone to lime induced chlorosis due to lack of iron when on alkaline soils.
33
3 plant examples for a neutral soil PH?
Vicia faba (broad bean)
Tulipa 'Queen of the Night'
Narcissus 'February Gold'
34
4 plant examples which prefer an alkaline soil?
Clematis montana
Lavandula augustifolia
Erysimum cheiri
Syringa vulgaris (common lilac)
35
What commonly occurs on Calcicoles grown in acidic soils? For example Clematis montana?
Calcicoles grown on acidic soils often develop the symptoms of aluminium toxicity - necrosis - reddening of the leaves and stunted growth.
36
Why are sandy soils more prone to becoming acid compared to clay soils?
Calcium will leech downwards when it rains as sandy soils are more porous. Loss of calcium results in an acidic soil.
37
State 3 harmful effects of very acid soil?
1. Decreased bacterial activity and worm activity so organic matter will not be broken down to make nutrients available to the plant.
2. Major nutrients become unavailable due to chemical reactions.
3. Certain plants such as Brassicas can get club root as the disease prefers acid conditions.
38
State 2 harmful effects of very alkaline soils?
1. Nutrients become unavailable particularly iron which results in PH induced interveinal chlorosis in acid loving plants.
2. Potatoes are prone to scab, a fungal disease.
39
Name 4 plants that will thrive in an acid soil? Acid loving!
Rhododendron 'Christmas cheer'
Camelia japonica
Acer japonicum
Arbutus unedo
40
Name 4 plants that will thrive in an alkaline soil?
```
CELS
Clematis montana
Erysimum cheiri (in the brassica family)
Lavandula augustifolia
Syringa vulgaris (lilac)
```
41
Describe 4 factors which makes a soil PH of 6.5 the most suitable for plant growth?
1. At pH 6.5 all nutrients are available to the plant if present as they are in solution, so easily absorbed by the roots.
2. Acid loving plants will thrive as iron is available at this PH so there is no interveinal chlorosis.
3. Worms and bacteria will still be actively breaking down any organic matter present, so making more nutrients for the plants.
4. If the soil is slightly acidic, it is easy to make it more alkaline by adding calcium compound such as lime if the soil is to be used for calcicoles such as Brassicas and to reduce the risk of club root.
42
List 3 types of mulch which can lower the PH of the soil?
Peat
Composted bracken
Pine needle compost
43
List 2 types of mulches that can raise the PH of the soil?
Crushed sea shells
Spent mushroom compost
Limestone chippings.
44
Describe 2 distinct mulching techniques which can be used to enable calcifuges (acid loving) plants to be grown well in alkaline soil.
Composted pine needles, composted bracken and leaf mould can be used as a mulch 5-8cm thick. These mulches are acidic in nature and so will lower the pH of the soil.
Spent mushroom compost should not be added as this is alkaline.
45
Describe 2 distinct watering techniques which can be used to enable calcifuges (acid loving) plants to be grown well in alkaline soil.
Watering with rain water would be preferred over tap water as rain water contains few minerals and so will not affect the pH.
Tap water om the other hand could contain calcium so could raise the pH of the soil making it more alkaline.
Sequestered iron fertiliser can be applied as a foliar feed diluted in water so that iron becomes available to acid loving plants such as Rhododendron 'Christmas cheer'. Rather than being unavailable in alkaline soils.
46
Describe 2 distinct Fertiliser methods which can be used to enable calcifuges (acid loving) plants to be grown well in alkaline soil.
Fertilisers containing ammonium compounds can raise the pH of the soil as ammonium contains H+ ions which lowers the pH and make the soil more acidic. Eg. Ammonia sulphate and ammonia nitrate.
Sequestered iron can be used as a foliar feed to make iron available.
47
What 6 materials can you incorporate into garden soil to make it more acid?
```
Composted bracken
Pine needles
Peat
Aluminium sulphate
Flowers of sulphur
Ferrous sulphate
Anything with sulphur when added to the soil will make it acid because sulphur plus soil water gives sulphuric ACID.
```
48
Give 5 examples of organic fertiliser?
```
Liquid seaweed
Fish, Blood and bone
Bone meal
Poultry manure pellets
Liquid comfrey tea or nettle tea
Also well rotted cow or horse manure act as a fertiliser and a soil improver.
```
49
Give 5 examples of inorganic fertilisers? Man made or Synthetic or naturally occurring mined minerals.
```
Growmore
Miracle Gro
Phostrogen
Sulphate of Ammonia
Sulphate of potash
Superphosphate
Tomorite
Rock phosphate
Osmocote (slow release)
```
50
Pros and Cons of Organic Fertiliser versus Inorganic Fertilser?
Organic
Limited fossil fuel in production.
Many organic fertilisers such as comfrey/nettle tea, worm tea can be made on site so environmentally friendly as no Co2 emissions to transport.
Inorganic are synthetic therefore high energy to produce and transport.
Organic
Bulky OM improves soil.
Inorganic
Does not improve soil as not bulky.
Organic
Precise nutrient content not known.
Difficult to over feed with nutrients from garden compost as low nutrient level, and releases slowly. Needs regular re-application.
Inorganic
Precise content is known.
Straight fertilisers are easy to over apply.
Organic
Slow acting and rely on bacteria and fungi to break them down so require moist warm conditions for optimal breakdown rate.
```
Inorganic
Fast acting (unless a controlled release fertiliser)
```
Organic
Naturally occurring - happens in nature anyway.
Inorganic
Can be mined from rock so damages environment. (rock phosphate)
Organic
OM feeds and sustains life in the soil.
Inorganic
Can lead to a build up of salts. (insoluble compounds) eg. houseplants.
51
Describe fertiliser as a top dressing?
The fertiliser is applied to the surface of the soil after planting.
52
Describe the fertiliser as a base dressing?
The fertiliser is incorporated into the soil before planting or sowing, or at the time of planting.
53
Describe the fertiliser as a liquid feed?
This is a soluble fertiliser dissolved in water and is applied to the root zone of the plant.
54
What are the 5 major plant nutrients?
```
Nitrogen
Phosphorous
Potassium
Magnesium
Calcium
```
55
Name one minor nutrient?
Iron
56
What is the role of nitrogen?
An ingredient of chlorophyll so important for photosynthesis. Makes proteins and also part of DNA.
57
What is the role of phosphorous?
Promotes healthy root development.
Part of the ATP molecule which is produced during respiration so important in high energy areas such as meristems in the roots.
58
What is the role of potassium?
Regulates water content so influences the quality of fruit and flowers.
59
What is the role of calcium?
Makes up part of the cell wall so essential for growth of root and shoot tips.
60
What is the role of magnesium?
Makes up part of the chlorophyll molecule so essential for photosynthesis.
61
Name 6 potential issues with growing plants in a container?
1. Limited root volume
Roots cannot grow beyond the confines of the container.
2. Water retention & supply
The only water source is the gardener. Once water supply is low the plant cannot access more.
3. Drainage
Media must be free draining or else the media will become saturated and roots will die. (as a consequence of a continued anaerobic environment)
4. Gas exchange
Difficult to maintain sufficient water availability whilst ensuring sufficient gas exchange - oxygen access and removal of co2 waste. The media must have large pore spaces that won't collapse.
5. Stability of compost
The media must have a stable structure to withstand varying degrees of watering.
6. Nutrients
Challenge of supplying large amount of nutrients in a small amount of water without causing scorching to the roots.
7. Partial sterility.
Container medium will not have the full soil buita that soil will, in other words partly sterile. This means its structure, water properties, porosity and nutrient availability will be different.
8. Root disturbance
Some plants don't like their roots to be disturbed when transplanted. Eg. Lathryus odoratus.
9. Cost/type of compost
Must be appropriate to the situation. Eg. nursery sales or annual bedding will not require high nutrient potting mix. Cactus compost is free draining.
10. Correct size of container.
Too small, and the plant will become pot bound. Too large is a waste of compost and also plant may not thrive due to a ring of soggy compost around the roots which is saturated and does not allow oxygen to reach the roots.
11. Shape
Square containers can be harder to fill properly to the corners, however they fit together better when there are lots of plants lined up on a bench.
12. Material of container - clay is porous plastic is not. But clay can dry out quicker. Plastic has environment impact.
13. Repotting/top dressing.
Permanent plantings will need repotting or top dressing with fresh growing media to encourage aeration and healthy root growth.
14. Vine weevil are a serious pest in a limited root environment and quickly become established.
62
Why is garden soil not suitable for a container?
Structure cannot be maintained with repeated wetting and drying.
The pore spaces collapse reducing aeration and drainage.
Fertiliser content is unknown.
May have the incorrect texture/structure for growing particular plants.
May be contaminated with salt for example when spreading in snow conditions.
May contain pathogens in the form of bacteria & fungi.
It will contain weed seed.
The ph is not known.
It may be too heavy.
May contain pests such as vine weevil.
63
What are the advantages of using growing media rather than garden soil?
```
Plant specific mixes are available to buy or make at home - eg. gritty loam for catcus.
Sterile - no weeds or pathogens.
pH is known.
Nutrient content is known.
Water retaining granules can be added.
It is stable and uniform.
```
64
How can the home gardener make different growing medium for different plants?
Home gardener can make up different growing media for different purposes by adding fertiliser, additives that change pH, perlite, or sharp sand to increase drainage for stem cuttings, vermiculite to increase water retention, water retaining granules for hanging baskets.
65
What is a loamless compost made from?
It is soilless.
Made from peat or peat substitutes.
Generally free of insects, weed seeds and disease.
Provides a uniform growing medium but are lighter and cleaner to handle than loam based.
66
What are loam based soils made from?
Soil based.
| John Innes.
67
Name 4 titles loamless compost ca be bought as bagged?
1. Multi purpose composts
2. Seed & cutting compost
3. Container compost
4. Ericaceous compost
68
Describe multipurpose compost?
Multi purpose composts - for wide range of purposes. Fine enough for seeds and a balance of nutrients to suit most plants for 4 weeks. Generally have lime added so unsuitable for calcifuge.
69
Describe Seed and Cutting compost?
Finer grade specifically for seeds, especially fine seeds and cuttings. Lower in nutrients, though phosphate maintained. Lime added
70
Describe Container compost?
Coarser, often can be used as a potting medium as well as for larger plants in containers. Lime is added. Higher in nutrients for long term nutrition.
71
Describe Ericaceous compost?
Specifically designed for calcifuges. Acid loving plants. Eg. Camelia japonica, Arbutus Unedo, Acer japonicum & Rhododendron 'Christmas cheer'.
72
Describe loam based composts (a range of John Innes) and their benefits?
Contain sterilized loam with added peat and sand for drainage and therefore aeration.
If purchased as John Innes it will be sterile.
Soil based medium heavier which is useful for pot stability with taller plants.
Also a bit more forgiving when it comes to water and fertility. Tend not to dry out so fast and tend to hold onto nutrients longer.
73
What is Air Filled Porosity? AFP?
The percentage of air after being saturated with water and allowed to drain freely. So good drainage too.
74
What is Water Holding Capacity? WHC?
The total amount of water a soil can hold at Field Capacity.
75
What 6 things for a good potting media?
1. Have good air filled porosity.
2. Have good Water holding capacity.
3. Free of pests and diseases, weeds and toxic compounds.
4. Not have excess soluble salts.
5. Have suitable pH
6. Have a stable structure.
76
Give 4 reasons why not to use Peat?
1. Peat is non renewable
. 2Extraction damages wildlife habitat, archaeology and climatic data.
3. Extraction affects the water table.
4. As peat used/extracted CO2 released contributing to greenhouse effect.
77
Give 4 examples of Peat substitutes?
Coir
Composted green waste
Composted wood fibre
Composted bark
78
Pros & cons of Peat?
```
Pros
Good Water Holding Capacity
Good Air Filled Porosity
Pathogen free
Cheap to prepare & transport
Low nutrient levels allows grower to dictate nutrient level.
Uniform & stable.
--------------------------------------------------------------
Cons
Acidic so needs lime adding.
Difficult to re-wet once dry
Environmentally unsustainable, damaging wetland habitats and CO2 release.
```
79
Pros & Cons of Coir?
```
Waste product from Coconut industry.
Pros.
Pathogen free
Waste product
Better water retention than peat.
Low in nutrients so grower can adapt to suit needs.
pH neutral
Lighter in weight.
Very like peat.
```
```
Cons
Air miles & carbon foot print
Does not hold onto nutrients well.
Consistency varies.
More expensive than peat.
Can be a nitrogen robber.
```
80
Pros and cons of composted green waste?
Council produced organic waste of varying quality.
Pros
More sustainable.
Recycled
Higher bulk density than peat or coir.
Weed free and low in pathogens as produced by hot composting.
High in nutrients for potting on.
Cons
Variable Water holding capacity & Air filled porosity.
High in nutrients so not suitable for seeds or cuttings
May contain glass and plastic.
81
Pros and cons of composted bark?
Pros
Slow rate of breakdown.
Moisture retentive
```
Cons
Difficult to rewet once dried out.
Nitrogen can be locked up by bacteria active on bark decomposition.
No nutrition
Very coarse texture.
Need to be sieved for sowing small seeds
```
82
What is ericaceous compost used for?
Acid compost 4.5-5 Loam based or loamless.
Specifically formulated for calcifuges.
Used to be made from peat with less lime added.
83
What is perlite and what's it used for?
Perlite is processed product from volcanic rock.
Light weight
Increases Air filled porosity of potting media
Decreases Water Holding capacity
Does not add or hold onto nutrients.
Good insulation properties for storing dahlias for example.
High energy to produce.
Can look unsightly when tipped into borders.
Good for house plants to prevent soil becoming compacted in containerised plants.
84
What is vermiculite and what is it used for?
Vermiculite is a processed product created by heating up clay.
Sterile
Contains plant nutrients Magnesium and Potassium
Improves drainage and Water holding capacity.
Light weight.
Used when sowing seeds. Creates humid environment.
High energy process to produce
Good for rooted cuttings.
Add to multipurpose compost to increase Water Holding Capacity.
85
Define what Hydroponics is?
Hydroponics is the science of growing plants in water to which nutrients have been added (liquid nutrient solution) rather than soil or organic composts.
2 techniques.
Nutrient film technique (NFT)
Substrate culture using Rockwool
86
How does the Nutrient Film Technique work?
Plants are grown in a shallow stream of water and nutrients which circulates around the system. Water is pumped from a reservoir along plastic troughs which are on a slope. The roots of the plants dangle in the moving water and absorb water and nutrients. The water then returns to the reservoir.
Because nutrient levels are monitored and environment controlled, (usually under glass) maximum yields obtained in short period of time.
87
What type of plants are grown by NFT? Nutrient Film Technique?
Herbs, lettuces, strawberries. Light in weight and do not need roots supported.
88
What are the benefits of Nutrient Film Technique?
High yield
Fast turnaround
Can grow all year round under protection.
Precise quantities of nutrients so no wastage.
Automated so low labour.
No soil borne pests and diseases.
All plants should be exactly the same - uniform growth.
Can add systemic insecticides/fungicides to system if there is a problem which is quick and easy.
89
What are the limitations of Nutrient Film Technique?
Costly initial setup for equipment
Can fail very quickly if not closely monitored - energy cut/contamination/pests/diseases.
Pumps use a lot of electricity. Energy also required for lights and temperature.
Difficulty disposing of waste water containing nutrients.
Different plants will require different setups, so have to grow same plants in a gully.
Very skilled as need to monitor nutrient and pH levels carefully.
Need a protected environment for commercial production.
Water supply has to be of good quality.
Hydroponic conditions create an environment that stimulates salmonella growth.
90
What is Hydroponic Substrate Culture system?
Hydroponic Substrate Culture is a way of growing plants in an inert substance such as rockwool, expanded clay granules, perlite or sand. The substrate supports the roots system and so is used for top heavy plants where root support is important, such as tomatoes, cucumbers and melons.
91
How does a Hydroponic Substrate Culture system work?
Plants are transplanted into Rockwool blocks similar to potting up plants in growing media.
Many irrigation techniques. Ebb and flow system, where roots are flooded standing in water for a while, and then drained and left. Repeated every 2 hours.
Or Top drippers used to water the Rockwool, and it's allowed to drain away into a gully and is recycled.
92
What are the benefits of a Hydroponic substrate culture system?
High yield and faster growth.
No weed seeds.
No soil borne pests and diseases
Can grow all year round under protection.
Clean system
Precise quantities of nutrients.
Can be automated - low labour.
Can add insecticides and fungicides to system.
All crops should be uniform.
Rockwool can be sterilised and re-used 3 or 4 times.
Can recycle water.
93
What are the benefits of a Hydroponic substrate culture system?
Costly initial setup for equipment.
Specialised skill to monitor nutrients levels.
Automated system can fail very quickly if not closely monitored. Power cut, contamination, pest and disease.
Energy required for pump if irrigation is ebb and flow but also for additional lighting and temperature.
A lot of energy required to make rockwool.
Need a protected environment for commercial growing.
Water supply has to be of good quality.
Disposal of water containing nutrient when it is cleaned and re-set.
Disposal of rockwool.
94
Situations where Water Culture is used?
Living Walls
Vegetable production
Interior Landscaping - house plants.
95
What are the environmental implications of growing plants in water culture?
Plastics are used for equipment.
Energy required to make the equipment. Carbon footprint.
Electricity is needed for automated system as well as for lights and temperature.
Allowance should be made for local water quality.
Discarding used solution can be hazardous as contains nutrients.
Rockwool is non biodegradable so there is a serious disposal issue. Can be recycled into new slabs now.
