R2102 - Understand the physical & chemical properties of soils Flashcards
1.1 What is weathering in soil formation?
Weathering is the breaking down of the parent rock by physical, chemical and biological means.
This produces a mineral soil.
1.1 Describe the natural processes of soil formation: Physical weathering (moving water, wind, freeze/thaw, heat, glaciers)
Moving water - streams, rivers or sea can carry rock particles and as the mix of water and rock flows over other rocks, fragments get broken off and these are further ground up by the water into smaller particles.
Wind - wind can carry abrasive particles that ‘sandblast’ exposed rock, common in hot countries where sand particles are readily blown about in the wind.
Freeze/thaw - rain water enters cracks/ joints within the rock, it freezes, forms ice which expands, then repeatedly thaws and re-freezes over time, which continuously widens the crack/ joint until the rock shatters into angular fragments.
Heat - In hotter regions rock surfaces exposed to the sun expand, whilst the rock within remains cool and this can set up strains within the rock causing the surface to crack and over time small fragments of rock to break away.
Glaciers - Ice in glaciers tends to stick to the adjacent rock and as it moves downhill the large rocks embedded in the glacier scour away any rocks they come in contact with causing the rocks to be fractured into smaller pieces.
1.1 Describe the natural processes of soil formation: Chemical weathering
Chemical weathering is where weak acids gradually dissolve rock.
Rain water combines with carbon dioxide in the air to form weak carbonic acid and this gradually dissolves chalk and limestone.
It can also react with many other minerals in rock, resulting in their gradual breakdown. .
1.1 Describe the natural processes of soil formation: biological weathering and addition of organic matter
Biological weathering is brought about by living organisms.
Biological weathering occurs when seeds are blown into rock crevices, take root and grow. The roots of plants exert great pressure and break up the rock.
Lichens and mosses produce CO2 through respiration and this forms weak carbonic acid which dissolves rock such as chalk and limestone.
When plants/ animals/organisms die their decomposition products, contribute to enrich the soil further.
The actions of micro-organisms decompose plant/ animal life to form humus.
1.1 What does loam mean?
- soil with roughly equal proportions of sand, silt, and clay
- an idealised soil for growing
1.1 What is a soil horizon?
A specific layer in the soil by digging a soil pit.
1.1 Describe the development of main soil horizons (4)
Organic: Leaf litter and other undecomposed plant material. Provides food for small animals such as earthworms, which are important in the decomposition process.
Topsoil: Uppermost layer dug during cultivation. Most important layer for gardeners. Between 10 and 40cm deep. Dark in colour due to the decomposed organic matter or humus it contains. Richer in plant nutrients as a result of decomposed organic matter. Contains most of the fibrous plant roots and soil organisms such as earthworms.
Subsoil: less fertile and much lighter in colour because it contains very little decomposed organic matter. Contains large tree and shrub roots that anchor the plants in the ground and also search out water.
Parent rock: original rock from which the soil is formed.
1.3 Define the term ‘soil texture’.
The relative proportions of the sand, silt and clay (mineral) particles in the soil.
1.3 What are the particle sizes of stones, sand, silt, clay (using Soil Survey England and Wales classification).
Stones: larger than 2mm in diameter
Sand: between 0.06mm & 2mm in diameter
Silt: between 0.002mm & 0.06mm in diameter
Clay: less than 0.002mm in diameter
1.3 Describe the characteristics of a sandy loam.
feel: gritty
nutrients: particles have no charge so nutrients are easily leached out of the soil
water retention: low water holding capacity but good water movement
temperature: large pore spaces containing air so will be quick to warm up in spring
1.3 Describe the characteristics of a silty loam.
feel: silky or soapy when wet
nutrients: plant nutrients will be held by the electrical charge on some of the particles but will also be available to the plants
water retention: large number of small pore spaces so will hold on to water but a high proportion of this water will be readily available to the plants
temperature: Slower to warm in Spring because of the large number of small pore spaces
1.3 Describe the characteristics of a clay loam.
feel: sticky when wet
nutrients: fertile because it has good nutrient retention due to the small negative charge on the particles
water retention: good water retention but not all the water is available to the plants
temperature: slow to warm up in spring because of all the water in the small pore spaces
1.4 Define the term ‘soil structure’.
The arrangement of particles in the soil.
How the particles (sand, silt and clay) are built, glued, cemented, or aggregated together to ideally form a “crumb structure” (peds).
1.4 Describe crumb structure and its influence on plant growth: Crumb formation
Soil crumbs are small rounded aggregates made up of mineral particles (sand, silt, clay) and organic matter.
Organic matter breaks down in the soil and forms humus. Humus coats the soil particles and allows them to aggregate or come together as crumbs.
A good crumb structure allows:
- Free water movement
- Gaseous exchange
- Thorough root exploration
1.4 Describe crumb structure and its influence on plant growth: Destruction.
- over cultivation too much digging or raking can destroy the structure
- cultivating at the wrong time of year for e.g digging a clay soil in winter when it is wet and sticky will cause compaction and damage the crumb structure
- failure to add organic matter regularly especially on a light sandy soil where it is broken down very quickly.
- over-watering can lead to the crumbs collapsing and forming a soil cap (a crust) when the soil dries out.
1.4 Describe the term saturation point.
Soil pores (large and small) are full of water and no oxygen is present. The soil is waterlogged.
1.4 Describe the term field capacity.
The amount of water the soil can hold against the pull of gravity. i.e the amount of water remaining in the soil a few days after having been wetted, and after free drainage has ceased.
The large air spaces are now filled with both air and water while the smaller pores are filled with water.
Field capacity is said to be ideal for plant growth.
1.4 Describe the term available water content.
Available water is the water that plants can actually take out of the soil.
It is the amount of water held by the soil between Field Capacity and the Permanent Wilting Point.
1.4 Describe the term permanent wilting point.
PWP is the water content of the soil when a wilted plant does not recover (retain turgor) overnight.
The point when water can no longer be extracted from soil.
1.4 Describe the term soil moisture deficit.
Soil Moisture Deficit is the amount of water required to return the soil to field capacity.
1.4 Describe the importance of an appropriate balance between air and water for the healthy growth of plants.
- A well-structured soil will have a good balance between water and air
- with water draining out of the large pore spaces by gravity, leaving them occupied by air
- but water still held in the smaller pore spaces and around the soil particles
- healthy growth requires a constant supply of water; too little rain and the plants will need irrigating whilst
- too much water can lead to the soil becoming waterlogged and plants dying, due to lack of oxygen around their roots
1.5 Describe irrigation methods - watering can.
- Plants need water at their roots which gets down into the soil rather than just damping down the top layer
- Use collected rainwater wherever possible
- It’s best to water cool of the evening or the very early morning, so that less water is lost immediately to evaporation
- well-aimed can of water will usually get down to the roots of the plant far better than a spray from a hose
- care should be taken to avoid damaging the crumb structure of the soil
- avoid disturbing the surface of the growing medium in containers by pouring water on too quickly
- watering seeds and cuttings, use a fine rose turned upward to minimize surface disturbance by large droplets of water
1.5 Describe irrigation methods - hose.
- Plants need water at their roots which gets down into the soil rather than just damping down the top layer
- It’s best to water cool of the evening or the very early morning, so that less water is lost immediately to evaporation
- a hose fitted with a trigger lance that can be adjusted for flow rate and fineness of spray is a good choice
- make sure you direct the water to the roots rather than spraying the tops of the plants and the foliage.
- avoid using a powerful jet of water as this can disturb the soil and cause damage to both soil and plants
- watering seeds and cuttings, use a fine mist turned upward to minimize surface disturbance by large droplets of water
1.5 Describe irrigation methods - sprinkler.
- a sprinkler is useful when you want to water a large area rather than just individual plants
- on bare soils the structure can easily be damaged leading to the formation of a surface cap.
- on slopes, runoff can cause erosion of the soil and loss of seeds and fertilizer.
- sprinklers are wasteful, watering everything within their range rather than just those plants that actually need it
1.5 Describe irrigation methods - seep hose.
fairly efficient method of applying water as delivers water very slowly to the soil, leaving plant foliage and most of the soil surface dry
a hose that is porous or has holes, laid on the soil allowing water to seep out
delivery rate can be adjusted to suit plant growth and temperature
made from recycled materials and biodegrade safely after a number of years
1.5 What is single single digging?
- Digging down to the depth of a spade, known as a spit (30cm)
- in shallow soils where topsoil may be less than a spit, dig to this level even if it’s less than a spit, to avoid bringing up subsoil.
- Dig out the first trench and move the soil close to where the last trench will be.
- Work backwards along the plot a second trench is then dug and the soil taken out of this second trench is inverted into the first trench.
- This process is repeated until the last trench on the plot is filled with the soil from the first trench.
- Annual weeds are buried. Remove deep rooted perennial weeds.
- Organic matter can either, be spread on the surface of the soil and turned into the trench with the soil, or it can be incorporated into the bottom of each trench.
- Dig heavy clay soil in Autumn so large clods are broken down by frost and snow to improve soil structure.
- Sandy soils are best dug in Spring.
- Never during frost or when covered with snow as this can harm soil organisms and the soil structure
1.5 Why single dig?
Why do it?
- Exposes the top ‘spit’ or spade depth to weathering, helping provide plant nutrients, improving drainage and burying weeds
- Improves soil structure (raises the soil surface, air is trapped and this increases total pore space, allows the incorporation of organic matter)
- Important in heavy clay soils (and compacted soils) in order to increase the porosity of the soil
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1.5 What is doubling digging?
Remove the soil from the upper and lower spits of the first trench and from the upper spit of the second, laying it aside in three separate clearly marked piles.
Soil may then be transferred from the lower spit of the second trench to the bottom of the first trench, and from the upper spit of the third trench to the top of the first. In this way topsoil and subsoil remain completely separate.
Continue digging further trenches in the same way, and at the end of the bed use soil saved from the first two trenches to fill the appropriate spits of the final two.
If the topsoil is more than two spits deep there is no need to keep the soil from the upper and lower spits separate.
Organic matter can be incorporated into the bottom spit.
1.5 Why/when double dig?
Improves uncultivated ground
if the soil is heavily compacted
if is a soil pan below the surface and drainage needs to be improved.
It is very important not to mix the topsoil and subsoil when double digging.
1.5 Describe rotary cultivation.
Rotary cultivators are used to create soil crumbs on uncultivated or roughly prepared ground instead of digging, forking and raking.
A rotary cultivator can be used to:
- prepare a tilth for seed sowing
- break up a soil cap
- incorporate green manures
- control annual weeds when preparing a stale seed bed
1.5 Describe forking.
Used on areas where loosening or breaking up the soil is the major requirement
Forking is less harmful to the soil structure than using a spade because it tends to break the clods along the existing natural fracture lines rather than along artificial ones created by the spade.
Suitable for rough digging and for clearing weeds from the soil surface.
Also used to improve the structure of soil that cannot be dug over, such as borders with established shrubs and herbaceous plants
1.5 Describe raking.
Raking is used on soil that has been roughly prepared by digging or forking.
It is used to level the soil, remove stones and produce a fine tilth ready for planting or seed sowing.
Fertiliser can also be raked in.
1.5 What are the advantages of bed systems?
Improving drainage – the soil is raised above the surrounding ground level
Increasing soil temperature - Soil in raised beds is better drained, so warms up faster in spring
Improving access - higher raised beds can be used for people who are less mobile or need to use a wheelchair
bulky organic manures are concentrated on a smaller area so it is easier to build up high levels of fertility
1.5 Describe ‘no dig’ method.
In most cases initial deep cultivation of the soil, incorporating organic matter to improve the structure is necessary before this method can be fully adopted.
Clear any weeds from the bed by hoeing, hand weeding
In the autumn add a 5cm layer of organic matter such as garden compost or well- rotted farm yard manure to the soil surface.
Within a short time this organic matter becomes incorporated into the soil by the action of earthworms.
In spring, plants and seedlings go directly into the soil.
This ‘no dig’ method means that there is less interference with the soil structure as it keeps soil disturbance to a minimum.
1.5 What is primary cultivation?
Involves the turning over of the soil
- Single and double digging by hand
- Mechanical ploughing and subsoiling
- Rotovating
1.5 What is secondary cultivation?
- secondary cultivation to produces a fine seedbed, ready for sowing seed or planting.
- Forking
- Raking
- Hoeing
- Consolidation
1.5 Describe consolidation.
Once the ground has been dug and raked level it needs to be consolidated by lightly treading.
This is done by walking over the area using the flats of the feet and small steps.
This action gets rid of the larger air spaces and allows for water to be drawn up through the very small pore spaces by capillary action.
It also ensures that the seeds will be in contact with the soil particles.
The soil is then raked to a fine tilth and the seeds are sown either into a shallow drill or broadcast.
1.5 Describe methods of improving drainage (getting rid of excess water).
Normal cultivation methods to improve soil structure and drainage
Soakaway – deep holes filled with rubble that penetrate to porous rocks, allowing water to filter through it
French drain – a gravel-filled trench lined with landscape fabric to keep soil and silt out of the gravel.
Raised bed
Appropriate planting – plants that can cope with waterlogged and marginal conditions
1.5 What causes excess water? (Identify causes of excess water)
soil texture eg a clay soil with a high proportion of small particles
poor soil structure caused by compaction, surface capping or a soil pan
surface run off when large areas are covered by roads, driveways, patios and car parks and water is unable to soak into the ground.
a high water table When the soil lies over impervious rock or very heavy clay, the water cannot drain away and much of the soil becomes saturated. The top of this level of saturated soil is called the water table.
a soil pan which is an impermeable layer that can prevent water draining away and water can back up above the soil pan forming a perched water table.
1.5 How can you identify poor drainage?
areas of standing water on the soil surface, this is called puddling
surface run off after heavy rain because the soil is already saturated
indicator plants such as mosses, rushes and sedges are growing in the area. Weed problems such as creeping buttercup, particularly in lawns.
permanently wet soil even in dry periods
smell of hydrogen sulphide – bad eggs
plants don’t grow well, stunted growth and a yellowish tinge to the leaves because they have poor or restricted roots
gleying - there may be a blue-grey colouring in the soil, this is due to a lack of oxygen
1.5 What are soil pans?
An impermeable layer in the soil which acts like a barrier to plant roots and as water is unable to drain away the topsoil is likely to become waterlogged.
may develop on a clay soil if there is repeated cultivation to the same depth with a rotary cultivator
or when iron particles are washed down through the topsoil and combine with the clay particles to form an impermeable layer
can be broken up by double digging or subsoiling
a soil pan should be visible if you dig a soil profile pit
1.5 Why add inorganic materials to soil?
- Lime – used to in a clay soil to improve soil structure by forming smaller aggregates
- Grit – for poorly draining soils to improve aeration
- Sand – can also be added to improve soil structure through improved drainage and aeration
1.5 Why add organic materials to soil?
- Improves soil structure and crumb formation
- In lighter, sandy soils is will bind particles together and improve water retention as well as preventing the leaching of nutrients
- Increases nutrients available to plants
- In heavy clay soils it will form smaller aggregates and improve drainage
- It will also increase the activity of soil organisms which will improve soil structure, e.g. earthworms tunneling through soil.
- Helps the soil heat up quicker since the material is darker
1.5 What is surface capping?
Surface capping can occur on light soils or when a fine tilth has been created in readiness for seed sowing.
Capping occurs when rainfall hits the soil surface causing the soil crumbs to break up and the fine particles then fill the gaps between the larger particles.
This makes it difficult for water to enter the soil causing puddles to form and the crumb structure to collapse even more quickly.
When the surface dries a soil cap is formed which hinders the exchange of gases and the emergence of seedlings through the soil.
Prevention: don’t create a seedbed too early in the year, but wait until weather conditions are more favourable. Apply mulch to light soils.
1.5 Describe signs of compaction?
- The larger pore spaces between the soil particles are compressed, resulting in slow drainage and increased surface run off. Less water is available to the plants so this results in poorer growth.
- Poor aeration leads to anaerobic respiration which can cause bad smells and a change in the soil colour.
- Soil is very hard and difficult to dig.
- Poor rooting of plants which causes slow growth and lower yields of fruit or flowers.
1.5 How can compaction be avoided?
- double digging or sub-soiling
- mulching
- incorporation of organic matter
- green manure
- timeliness of cultivation and not walking on wet soil
- avoiding the use of heavy machinery
- varying the depth of cultivation when using a rotary cultivator
2.1 What is dead organic matter?
Remains of anything once alive (plants or animals) falling to or present on soil surface. Provides a food source to organisms as they breakdown and decompose.
2.1 What are the benefits dead organic matter in the soil?
Benefits of dead organic matter in the soil
- microbial activity is increased because it is food for soil organisms
- soil is physically opened up and aeration improved by the dead but recognisable organic matter
- water-holding capacity of the soil is improved by fine (unrecognisable) organic matter
- it is a dilute source of slow release nutrients as the organic matter decomposes and releases minerals
2.1 What is living organic matter (living organisms) in soil?
- Living organisms such as plants, earthworms, insects, fungi and bacteria.
- Organisms contribute to the decomposition of organic matter and the formation of humus.
- Affects soil structure by moving soil and creating a network of interconnected tunnels, which improve aeration and water movement
2.1 What are the benefits of organic matter (living organisms) in the soil?
- convert plant and animal debris into minerals and humus
- soil structure is improved by the activity of plant roots, earthworms and other burrowing organisms
- detoxification of harmful organic materials such as pesticides is undertaken by many bacteria species
2.1 What is humus?
- Humus is a sticky black jelly-like substance which is the end product of the decomposition of organic matter.
- It coats the soil particles making the soil darker in colour
- On light sandy soils it helps to bind the particles together
- in a clay soil it forms clay–humus complexes, breaking up the lumps of clay and creating a more crumb –like structure
- has a buffering effect, as like clay, it carries a small electrical charge so it is able to hold on to plant nutrients and prevent them from being leached out of the soil
2.1 What are the benefits of humus in the soil?
- in both sandy and clay soils it improves soil structure by coating the soil particles and forming stable crumbs
- it improves drainage in a clay soil
- the surface charge on humus means that the buffering capacity of the soil is increased as it holds on to plant nutrients, preventing them from being leached out of the soil
- because humus is black the soil warms up more quickly in spring
- it improves the water holding capacity as it acts like a sponge which is useful on light, sandy soils
- it provides food for soil micro-organisms
2.2 Describe the characteristics, uses, benefits and limitations of farmyard manure.
Characteristics: Horse or cow. Consists of bedding material such as straw or wood chips mixed with animal faeces and urine. Should be well rotted for at least a year as fresh faeces and urine contain ammonia which can burn the plant roots.
Uses: Improves soil structure. If well- rotted can also be used as mulch around trees, shrubs and roses.
Benefits: Supplies nutrients, improves soil structure
improves water retention
Limitations: Nutrient level is variable and can be quite low, scorching will occur if not well rotted or added at the same time as lime
2.2 Describe the characteristics, uses, benefits and limitations of garden compost.
Characteristics: Dark brown, crumbly texture. Decomposition of organic matter as a result of the actions of worms and micro-organisms.
Uses: Soil conditioner, mulch, well made can be mixed with other materials to make potting compost, can be basis of no dig bed system
Benefits: Positive effect on soil structure if correctly made. Sustainable as uses waste products. Free
Limitations: If not heated to a high enough temperature will contain weed seeds and pests. Takes time to make.
2.2 Describe the characteristics, uses, benefits and limitations of mushroom compost.
Characteristics: By product of the mushroom industry. Almost all made from composted straw mixed with chalk. Has a high pH.
Uses: Soil conditioner or mulch. An alternative to lime when growing brassicas as high pH helps prevent club root.
Benefits: Excellent source of organic matter with added nutrients. Cheap.
Limitations: Use is limited as can’t be used with plants that prefer acid conditions i.e calcifuges (e.g. camelias, rhododendrons, magnolias) Leftover fertiliser levels may be unsuitable for young plants.
2.2 Describe the characteristics, uses, benefits and limitations of composted green waste.
Characteristics: Dark brown, crumbly texture. Essentially the same as garden compost but has normally been heated sufficiently to inactivate harmful weed seeds and diseases.
Uses: Soil conditioner or mulch on beds, borders or container grown plants.
Benefits: Locally produced so reduces transport costs and emissions. Available in bulk. Cheap and sometimes free.
Limitations: Can be contaminated with very small particles of plastic and glass. High pH.
2.2 Describe the characteristics, uses, benefits and limitations of leaf mould.
Characteristics: Made from the rotted leaves of deciduous trees.
Uses: Improves soil structure, a good mulch as it doesn’t contain weed seeds. Can also be mixed with other materials to make potting compost.
Benefits: Easy and free to make.
Limitations: Low in nutrients, takes long time to make
2.2 Describe the characteristics, uses, benefits and limitations of chipped bark.
Characteristics: Chipped or shredded bark. Decorative.
Uses: Mulch or a weed suppressant when used with woven polypropylene fabric. Used in public planting schemes.
Benefits: Long lasting, available in several different grades. Reduces evaporation and suppresses weed growth.
Limitations: Light when dry so can be blown about in the wind and it floats on water. Birds throw it about when looking for food so can become untidy.
2.2 Describe the characteristics, uses, benefits and limitations of composted straw.
Characteristics: Can either be produced in the garden or purchased as a mineralised composted wheat straw product called Strulch which last up to 2 years and gives a brown earthy colour.
Uses: Mulch
Benefits: Not liked by slugs and snails. Strulch lasts up to 2 years and can then be worked into the soil. Organic.
Limitations: Hard to make at home. Strulch is expensive.
2.2 Describe the characteristics, uses, benefits and limitations of green manure.
Characteristics: Source of organic matter. Plants are grown in the soil as a crop and then incorporated into the soil before the next crop is sown.
Uses: Cover bare ground, compete out weeds, reduce soil erosion, capture soluble nutrients that would otherwise be leached, add organic matter, to increase micro-organism activity in the soil, develop and maintain soil fertility and structure.
Benefits: Release nutrients, especially nitrogen, back into the soil.
Limitations: Adds very little in the way of long term improvement to the soil structure.
2.2 Describe the characteristics, uses, benefits and limitations of crop debris.
Characteristics: Crop debris after harvesting, often left on the surface or turned back into the soil.
Uses: Mulch, nutrient supply.
Benefits: Inexpensive way of adding organic material to the soil instead of composting it. No cost.
Limitations: Unlikely to be of great benefit on its own, and the nutrient value will depend on the crop.
2.2 State the purpose of mulching.
Mulches are materials (organic or inorganic) added to the soil surface in order to provide one or more of the following:
- a decorative finish to a bed or border e.g. chipped bark on borders and large scale shrub plantings
- prevent weed growth
- aid moisture retention
- protect the soil surface and reduce soil capping and erosion
- improve soil structure as it gets drawn down into the soil by earthworms (organic)
- maintain or increase the amount of organic matter in the soil (organic)
- add some nutrients to the soil (organic)
- stimulate beneficial soil organisms (organic)
- modify or even out the soil temperature
- protect edible crops from soil contact or rain splash eg straw under strawberries (organic)
2.2 List and compare organic and inorganic materials for mulching.
Organic: Composted straw, leaf-mould, chipped or shredded bark, spent mushroom compost, local authority compost and well-rotted farmyard manure.
Inorganic: pebbles or gravel, slate, stone chippings, recycled tumbled glass. Sheets such as woven polypropylene (geo textiles) allow air and water through but supress weed growth. Black polythene can also be used to suppress weeds but it’s not permeable.
Soil structure:
- Any organic mulch will break down gradually to release nutrients into the soil and help improve soil structure.
- Inorganic materials don’t add nutrients or organic matter to the soil
- Sheet mulches or woven fabrics do not boost the fertility or improve the structure of the soil. Once in place organic matter cannot be applied to the soil.
Sustainability:
Inorganic materials are long lasting. Environmental issues/damage when extracting/transporting. Sheets can’t be recycled. Expensive.
Inorganic materials: Organic mulches and those using recycled materials are more environmentally friendly than the manufactured inorganic materials. Relatively low cost.
2.2 State the effect on the soil of green manures.
Green manures are usually sown in late summer or autumn. As they grow they mop up any nutrients in the soil, preventing them being leached out.
When the crop is dug-in, the following spring, these nutrients are released back into the soil and the plants also contribute organic matter.
Most green manures reduce the alkalinity of the soil by producing humic acid.
Most vegetables like a high pH so you may need to lime the soil after the addition of a green manure.
Examples: Agricultural - Winter grazing rye, winter tares Garden - peas and annual lupins
2.3 What is garden compost?
Garden compost is the breakdown or decomposition of organic matter as a result of the actions of worms and microorganisms
2.3 Describe the importance of the following in the process of composting: choice of material, ratio of green to woody material, aeration, moisture content, lime, pH, temperature, insulation, accelerators, volume, establishment and development.
choice of material: a mix of green and brown materials. Green materials - leafy vegetables, grass cuttings, soft stems, kitchen waste Brown materials - woody tree and shrub prunings, paper, cardboard and wood chippings (shredded to help speed decomposition)
ratio of green to woody material: 1 part green to 2 parts brown
aeration: beneficial organisms are aerobic so require well aerated conditions. Turning the heap on a regular basis prevents compaction and improves aeration.
moisture content: The micro-organisms, the bacteria, that bring about decomposition require water and become inactive if the compost heap is too dry. Once the heap is moist enough it should be covered to keep out excess rain and retain heat.
pH and lime: The micro-organisms require a neutral pH to work efficiently so if the compost heap becomes too acidic the bacteria will stop working. Thin layers of lime can be added to the heap to raise the pH.
temperature: The rate at which the micro-organisms break down the organic matter also depends on the temperature within the heap. Under ideal circumstances the temp can rise to 70. The composting process gives of heat and this speeds up the natural breakdown of organic matter. Most garden composting does not go to a high enough temperature to kill harmful organisms and weed seeds.
insulation: Reduces heat loss from the surfaces but this also reduces the flow of air into the heap. Regular turning is necessary for aeration.
accelerators: can help to speed up the process when there is not enough green material available and the process then slows down due to lack of nitrogen. Artificial fertiliser such as ammonium sulphate, a proprietary accelerator or farmyard manure can be used.
volume: Heap size is important as heat is generated by the actual process of decomposition within the heap.
establishment and development: Compost bins can be bought, but slatted, wooden sided bins can be made quite easily. They need to be of a reasonable size and a bin of 1 cubic metre is ideal. A suitable lid or a cover such as old carpet is needed to keep the warmth in and the rain off. Turn once a month, water if dry. Compost should be ready in 3 months spring/summer & 6 months winter.
2.3 Describe how to make and use comfrey and nettle tea in order to supply nutrients.
2.3 What is comfrey/nettle tea?
Comfrey tea (rich in potassium) or nettle tea (high in nitrogen) are organic infusions where leaves are soaked in water and used as a fertiliser or foliar feed.
2.3 Describe the creation of hot a bed.
Use fresh horse manure mixed with materials you’d otherwise put on your compost heap. Or just usual composting material if manure not available.
Position in a sunny, sheltered, well-drained corner of the garden. Well prepare soil. Construct a rectangular frame about 1.2m long by 0.6m wide from old planks or from concrete blocks. Or you could do this in a greenhouse border or polytunnel.
Fill the frame with green waste and manure. Make sure the heap is loose so that there is plenty of oxygen.
Within two to three days the pile will heat up and generate steam. Invert the pile and fluff it up to introduce more oxygen.
Repeat this process three days later sprinkling the heap with water, if necessary, to keep it moist.
After nine or ten days the material is trodden down firmly. It will now heat up very quickly.
The heap can be covered with a cold frame, cloches or lights (panes of glass) to make the most of this bottom heat. Stick a long soil thermometer into the centre of the heap and watch the temperature rise. It will peak and then drop to about 24oC. (75o F).
At this point add a 15cm layer of topsoil or a used grow bag to the top of the heap and sow seeds or plant into this soil.
Feb or March grow early crops such as lettuce, spinach and spring onions. Late April frost tender crops including French and runner beans, courgettes, squash, outdoor tomatoes and sweetcorn.
In autumn the well-rotted heap can be used as a mulch or dug into the soil.
2.3 Describe the creation of a wormery.
Compost from worms is highly fertile. The most productive are red brandling worms and striped tiger worms. These can be purchased, but they are the worms that you will find wriggling about in your compost heap.
Container can be a plastic dustbin fitted with a tap to drain of the liquid, which can be diluted and used as a liquid feed for plants.
Place gravel or sharp sand in the bottom.
Add a layer of damp straw or shredded newspaper which will be the worms bedding until the process begins.
5cm of chopped kitchen waste is then added and once the worms have been introduced into the bin they are covered with a layer of wet newspaper to keep out the light and maintain moisture levels.
Place a lid on the bin and a temperature of between 20oC and 25OC is maintained.
Keep adding layers of kitchen waste, no more than 15cm in depth, and allow the worms to work most of it before adding more.
Drain of the liquid.
When the bin is full, separate the worms from the compost by sieving and start the process again.
2.3 Describe how to make and use comfrey or nettle tea in order to supply nutrients.
Equipment: Comfrey/nettle leaves, gloves, shears or secateurs, a hessian sack, container with lid (ideally black as will absorb heat), something to stir with, water, plastic bottles such as old milk bottles
Harvesting Before the plants flower and are 60cm high, cut them down to 5cm above ground level. Make sure you select healthy pest and disease free leaves. Chop the leaves up.
Procedure: Pack 900g of leaves into the hessian sack and suspend it in a container with a lid (this is to contain the smell which develops as the leaves decompose). Then fill the container with water. Next place the container in a nice sunny spot in the garden to keep it warm. Stir the mixture to keep it aerated. Foaming indicates that the leaves are decomposing. When the foaming stops (after about 4 weeks) the liquid can be drawn off. Store the liquid in plastic bottles in a cool dark place.
Application: Dilute the liquid 1:10 with water. The fertiliser can be applied to the roots of tomatoes, cucumbers, clematis and any other plants where you want to encourage flowers, fruit or vegetables. It can also be used as a foliar feed but must be applied in dull weather to avoid leaf scorch.
2.3 What is a hot bed?
A hotbed is where heat is generated from decomposing organic matter within a protected environment such as a polytunnel or cold frame.
3.1 Name the major (5) and minor (1) plant nutrients.
Major:
- Nitrogen N
- Phosphorus (phosphate) P
- Potassium (potash) K
- Magnesium Mg
- Calcium Ca
Minor: Iron Fe Iron
3.1 Nitrogen N - describe role, deficiency and excess.
Role: Needed in large amounts for leafy, green, vegetative growth. Constituent of the green pigment chlorophyll found in leaves and green stems. Easily leached out of the soil. Levels are usually low in late winter/ early spring so spring is a good time to apply a nitrogen fertiliser.
Deficiency: Slow, spindly growth. Yellowing of older leaves (chlorosis) due to lack of chlorophyll. May be preceded by blueing of the older, lower leaves. New leaves may be pale green.
Excess: soft, lush leafy growth making the plant vulnerable to pest and disease attacks and more likely to be damaged by cold.
3.1 Phosphorus P - describe role, deficiency and excess.
Role: Important in the production of the major chemical required for energy transfer in the plant (adenosine triphosphate, ATP). Required in large amounts where rapid cell division takes place, meristems of the root and stem. Large amounts are concentrated in seeds in readiness for germination. Critical at the seedling stage and the growing root has a high requirement. Emerging root needs to extract phosphorus from the soil before using up reserves in the seed. Phosphorus is constantly being recycled from the older parts of the plant to the new growing points.
Deficiency: Poor root growth which in turn leads to poor growth of the plant. There can also be bluish or purple stem and leaf colourings with or without speckling.
Excess:
3.1 Potassium K - describe role, deficiency and excess.
Role: Needed for good flower and fruit formation. Increases the general hardiness of the plant making it more resistant to cold, drought and disease. Present in relatively large amounts in plant cells where it helps to regulate osmosis.
Deficiency: Brown scorched areas on the leaf tips and margins. Low potassium levels will result in poor flowering and fruit formation and this is made worse if large quantities of nitrogen are added.
Excess:
3.1 Magnesium Mg - describe role, deficiency and excess.
Role: Needed in large quantities to make chlorophyll. It is actually part of the chlorophyll molecule.
Deficiency: Yellowing of the leaves between the veins. This is called interveinal chlorosis and it appears on the lower, older leaves. This happens because the older leaves release magnesium from their chlorophyll and this magnesium is then moved around the plant and used to make chlorophyll in the new, young leaves.
Excess:
3.1 Calcium Ca - describe role, deficiency and excess.
Role: Forms calcium pectate in the plant, a major constituent of plant cell walls. Also required for activity in the meristems, especially the root tip.
Deficiency: Causes weakened cell walls and this shows up as inward curling pale young leaves and sometimes death of the growing point. Specific disorders include ‘topple’ in tulips when the stem is too weak to support the flower, ‘blossom end rot’ in tomatoes and ‘bitter pit’ in apples.
Excess:
3.1 Iron Fe - describe role, deficiency and excess.
Role: Involved with chlorophyll production. Although it is not part of the chlorophyll molecule it is a component of some of the enzymes that are needed to synthesise it.
Deficiency: Yellowing of the young leaves between the veins. deficiency is commonly caused by the presence of large quantities of lime. This lime-induced chlorosis occurs on over-limed or chalky soils.
Excess:
3.2 Describe what is meant by the pH terms: acidic, neutral and alkaline.
Soils are classified as acid, neutral, or alkaline and this factor influences the plants that can be grown in a particular soil.
The pH scale is used to measure the acidity or alkalinity of a soil.
The pH scale goes from 1 to 14.
Acidic: below 7 is acid
Neutral: 7 is neutral
Alkaline: above 7 is alkaline
3.2 State the pH range found in garden soils.
The soils of Britain and Ireland are usually between pH 4 and 8, the vast majority being between 5.5 and 7.5.
3.2 State why 6.5 is the most suitable pH for a wide range of plants in the British Isles.
The ‘ideal’ pH for most plants is a pH of 6.5 because at that point all the essential nutrients are available for uptake by the plants.
There are considerable differences in the tolerance of plants to soil pH but many will grow quite happily in soil of a roughly neutral pH between 6 and 7.
3.2 State the effects of soil pH on soil structure (soil organisms, crumb formation) and nutrient availability (lime induced chlorosis).
Organisms - worms and bacteria that breakdown organic matter in the soil do not like acidic conditions so the rate of breakdown slows or stops in acid conditions.
Crumb formation - the addition of lime usually improves soil structure because raising the pH can create more favourable conditions for beneficial organisms. This leads to the decomposition of organic matter yielding humus and this helps crumb formation in both sandy and heavy clay soils. Calcium rich clay soils tend to crack and crumble more readily.
Nutrient availability - Calcifuges, plants that are adapted to growing in soils with a pH between 4.5 and 5.5. A pH above 5.5 means the lime in the soil interferes with the uptake of iron in these plants and they develop lime-induced chlorosis.
3.2 Identify materials used to influence the soil pH, lime. State the benefits and limitations (environmental, health and safety issues, timing of application, effectiveness of the material).
More lime has to be added to clay soil than sandy soil. See table below.
When applying more than 0.5kg per sqm, it is best to dig half into the soil and sprinkle the rest on the surface after digging.
When applying less than 0.5kg per sqm, dig the entire amount in, but you can sprinkle it on the surface if digging is not practical.
Benefits: Raises the pH, provides the nutrient calcium, encourages worms and beneficial bacteria, discourages diseases such as clubroot in brassicas, makes clay soils more workable by flocculating the particles, can make other nutrients more available
Limitations: Does not have an immediate effect best applied in autumn and combined with digging. Over-liming may cause nutrient deficiencies. Can’t apply at the same time as manure as the two can react, causing loss of nitrogen in the form of ammonia. Lime and manure on alternate years.
Health and safety: Wear gloves and goggles as can irritate the skin or eyes
3.2 Identify materials used to influence the soil pH, sulphur. State the benefits and limitations of each (environmental, health and safety issues, timing of application, effectiveness of the material).
The pH can be lowered by the addition of sulphur which is converted to sulphuric acid by soil micro-organisms.
The amount of sulphur required depends on the same factors as for lime; that is, the pH change needed and the soil texture. More sulphur is required for clay soils.
Soil-acidifying materials can be applied at any time of the year, but take longer to work in cold soil so best applied spring to autumn.
Sulphur is best incorporated, by cultivation, into the soil in advance of planting so it has plenty of time to take effect. Applied to the surface it can take years for the acidity to be changed at root depth.
Gloves, goggles and dust-mask are sensible precautions
Needs reapplication to maintain acidity.
3.2 Identify materials used to influence the soil pH, organic materials. State the benefits and limitations of each (environmental, health and safety issues, timing of application, effectiveness of the material).
Spent mushroom compost raises pH as an alternative to liming.
3.2 What are Calcifuges? Name 3 examples.
A calcifuge is a plant adapted to grow in acid soils below pH 5.5. (a fugitive fleeing from lime) Acid low pH.
- Camellia japonica
- Erica cinerea
- Rhododendron luteum
3.2 What are Calcicoles? Name some examples.
A Calcicole is a plant adapted to grow in calcareous (calcium-rich, chalky) soils. Alkaline, high pH.
- Viburnum tinus
- Buddleja davidii
- Clematis alpina
3.2 Give 3 named plant examples for Neutral soil.
A pH of 7 is considered neutral. Many plants grow in neutral soil.
- Alchemilla mollis
- Nigella damascena ‘Miss Jekyll
- Myosotis sylvatica
3.3 What are fertilisers?
Fertilisers are concentrated sources of plant nutrients, usually in compact form such as pellets, granules, powders or liquids. They are used to improve plant growth and yields. They can be either organic or inorganic in origin.
3.3 What is a soluble fertiliser? What is a slow release fertiliser? One named example for each.
soluble fertiliser: Dissolves immediately in water. Applied direct to soil to dissolve in soil water or made into a solution and applied by watering can or hose.
Too much is harmful to plants causing reverse osmosis. Also excess can leach out and contaminate ground water, ditches and water courses.
- ammonium sulphate N (inorganic)
slow release fertilisers: Do not dissolve immediately in water but provide nutrients in soluble form over a long period of time. Usually under the influence of soil micro-organisms to release their nutrients and are dependant on soil temperature.
Hoof & horn and bone meal (organic) P N
3.3 What is a straight fertiliser? What is a compound fertiliser? One named example for each.
Straight fertilisers: supply only one of the major nutrients, nitrogen, phosphorus, potassium, or magnesium. They are usually just sold under their chemical name.
- ammonium sulphate supplying N
- potassium sulphate supplying K
Compound fertilisers: supply two or more of the major nutrients, nitrogen N, phosphorus P and potassium K. The accepted convention for describing the nutrient content of a compound fertiliser is to put the content in the order N P K.
- Growmore (inorganic)
- Blood, fish and bone (organic)
3.3 What is a controlled release fertiliser? One named example for each.
Controlled release fertiliser: Release nutrients in a controlled way over a specified length of time; 3 months, 6 months or longer. Expensive and not economical for garden wide use. Good for long term container plants.
- Osmocote: granules covered with a semi-permeable coating of biodegradable resin. (inorganic)
3.3 State what is meant by EACH of the following terms: liquid feed, foliar feed, using ONE NAMED situation to illustrate the use of each.
Liquid feed: fertilisers dissolved in water then applied to the soil or compost. E.g. Use liquid tomato feed in the greenhouse to promote fruit production
Foliar feed: a liquid feed diluted sufficiently so can be applied to leaves without causing scorch. Fast acting, can be used when soil is too dry for granular feed. Best applied early morning by spraying the leaves until there is run off. E.g. Application of minor nutrients (trace elements) to raspberry canes growing on a high pH soil showing signs of iron or manganese deficiency.
3.3 State what is meant by EACH of the following terms: base dressing, top dressing, using ONE NAMED situation to illustrate the use of each.
Base dressing: when a fertiliser is applied during the final stages of soil preparation before sowing or planting. Rate of application is usually 60 g per sq m. Fertiliser should be spread evenly over the surface and forked or raked in to the top 10cm of soil. E.g Superphosphate applied to a seed bed
Top dressing: fertiliser applied to established crops or plants. Most effective if lightly forked or watered into the surface of the soil. E.g. Applying Growmore (equal amounts N,P,K) to an established mixed border in spring.
3.3 State the benefits and limitations of nutrient sources (environmental, health and safety issues, timing of application, variability of the material).
Health and safety: Dangers to users skin, eyes, breathing during application
Environmental: Inorganic - materials from non renewable resources, high carbon footprint from production, can leach into water courses, detrimental to microorganisms and other wildlife, can change soil pH over time
Variability of material: Inorganic- nprecise in nutrient content, Organic - nutrient ratio can be variable
Timing: Usually during spring/summer, some organic slow release fertilisers can be applied late winter early spring
Nitrogen fertilisers: apply in spring to encourage vegetative growth.
Potassium: Apply in spring, summer or autumn to encourage flower and fruit formation. Also makes plants hardier and better able to withstand cold in winter.
Phosphorus: Should be applied at least two weeks before sowing seeds or planting so it can slowly dissolve in the soil solution and be available as the seeds start to germinate. Encourages root formation.
4.1 State the limitations of using soils in containers.
- crumb structure will not withstand the constant watering becomes compacted
- loses structure very quickly, large pore spaces collapse, reducing the amount of air in the and restricting drainage.
- may contain weed seeds, soil born pests and diseases.
- very heavy when wet, making it difficult to move larger pots around
- variable, unknown amount of the required nutrients
- variable pH level
4.1 Explain the considerations required when growing plants in containers. Restricted root volume, water retention & supply, drainage, stability of compost materials, nutrients, partial sterility, weight/density.
Restricted root volume: Roots cannot go out in search of water and nutrients as they would do in the soil. So careful consideration must be taken to ensure all the plant’s water and nutrient requirements are met.
Water retention & supply: Growing media should have good water holding capacity. Don’t fill compost to the top of the pot, leave space for watering. Water retaining granules or vermiculite can be used.
Drainage: Media must be free draining, else it will become saturated and roots will die. Container must have sufficient drainage holes.
Stability of compost materials: Media must have a good, stable structure so that roots can anchor and the medium does not ‘slump’ and become airless. Must retain physical properties when inorganic fertilisers are added or when it is mixed with other ingredients and be able to withstand varying degrees of watering.
Nutrients: Roots can only access the nutrients that are available in the container. It’s crucial to supply the correct amount of nutrients without scorching the roots or overdosing.
Partial sterility: Means that most pathogens and weed seeds are killed off during processing which is particularly important for seed sowing growing media. However, there are also beneficial bacteria and fungi in garden soils and these will not be present.
Weight/density: Growing media which contains loam , are heavier than those which are made of just decomposed organic matter. This is useful for making large pots more stable and less likely to blow over, but they can also become compacted over time.
4.2 Describe a range of compost types: peat based, peat free (coir, composted green waste, composted bark)
Describe ONE NAMED situation to illustrate the use of each compost type.
Peat based: Loamless (soilless) made from organic matter which is peat. Peat is partially decomposed organic material formed in waterlogged soil, in bogs and fens. Pathogen and weed free, uniform in texture, stable, acidic and contains very little nutrients. Uses: Multipurpose - seeds, cuttings, larger plants and containers
Peat free: Loamless (soilless) made from organic matter which are peat substitutes.
Coir:(coconut fibre from Sri Lanka), a waste product of the coconut industry. Excellent water-holding ability, sufficient mix of fine and coarse fibres to hold air in its pore spaces. Does not hold nutrients well.Uses: suitable for short term plants such as spring or summer bedding but watering and feeding can be difficult to manage.
Composted green waste: Due to high nutrient content and high pH, tends to be mixed with other materials to make potting compost- no more than 30% of the overall product. Uses: Mulch, soil improver, potting compost if mixed with other medium
Composted bark: Excellent drainage properties and a low pH. Uses: Suitable for potting on seedlings and for growing plants on.
4.2 Describe a range of compost types: Ericaceous, loam based
Describe ONE NAMED situation to illustrate the use of each compost type.
Ericaceous: For calcifuges (acid loving plants) adapted to grow on soils below pH 5.5. Uses: Good for containers when garden soils are too alkaline for ericaceous plants.
Loam based: Soil based, sterilised to eliminate fungi, insect pests and weed seeds. Needs to have sufficient clay and organic matter present to give good structural stability. Peat, coarse sand or grit are added. Peat improves water retention whilst the coarse sand ensures free drainage and aeration. Uses: To provide stability for larger container grown plants.
4.2 Describe a range of compost types: seed compost, potting compost, multi-purpose compost
Describe ONE NAMED situation to illustrate the use of each compost type.
Seed compost: A finer grade of compost specifically for seeds and cuttings. A short term compost due to low nutrient levels. Uses: Planting seeds
Potting compost: A coarser grade of compost, often can be. Higher in nutrients for long term nutrition. Uses: Potting on medium for larger plants in containers.
Multi-purpose compost: Fine enough for seeds with a balance of nutrients that suit most plants up to about 4 weeks. Generally has lime added so suitable for a wide range of plants but not for acid loving plants (calcifuges). Controlled release fertiliser can be added to provide nutrients for potting on larger plants. Uses: seeds, potting on, larger container plants
4.2 Identify the environmental implications of peat in growing media.
- a non-renewable resource
- its use causes the loss of a natural habitat for birds and flora
- CO2 is given off once the peat is exposed to air
4.3 State what is meant by the term hydroponics.
Hydroponics or water culture involves the growing of plants in a nutrient solution without any soil or growing medium.
4.3 Explain the considerations required when growing plants in water culture. Aeration, nutrient supply, nutrient levels and pH control, water supply and quality, pest and disease control, automation.
AERATION: Roots need air to respire efficiently. In circulating hydroponic systems oxygen has to be introduced into the water flow.
NUTRIENT SUPPLY/LEVELS AND PH: As water circulates through the system the nutrients are used up by the plant and need to be topped up using a dosing system. Adding nutrients can alter the pH and make it more acidic, buffering agents act against this to restore correct pH level.
WATER SUPPLY AND QUALITY: Constant supply is needed. Most systems operate on a closed system of recirculation and topping up when necessary. Water needs to be monitored for quality especially if drawn from aquifers (a body of rock/sediment olding groundwater).
PEST AND DISEASE CONTROL: Dangers of both air and waterborne pests and diseases are high in such intensive mono-culture systems.
AUTOMATION: Hydroponic systems involve complex computerised monitoring and dosing systems which need to be calibrated correctly and regularly maintained.
4.3 Describe the NFT (nutrient film technique) method of growing plants in water culture.
Plants are grown in plastic, open-ended troughs or gullies lined with capillary matting through which a thin layer of nutrient solution is continually passed.
The gullies are on a slight slope to enable flow.
A mat of roots develops in the nutrient solution and in the moist atmosphere above.
The nutrient level in the solution is controlled and adjusted by a computer programme.
4.3 Describe the substrate culture (rockwool) method of growing plants in water culture.
Rockwool provides a lightweight, absorbent, inert and sterile rooting medium.
It is supplied as polythene wrapped slabs and cubes on which the plants are grown.
Holes are cut in the polythene for the plants, which are drip fed with a complete nutrient solution from the top, with the surplus running out through the bottom of the slabs.
The nutrient solution is collected in a storage sump and used to irrigate outdoor crops.
4.3 State the situations in which water culture can be used, to include: green walls, vegetable production (tomatoes), interior landscaping
- Green walls are used to improve the environment reducing air pollution and noise and to insulate buildings.
- There are now numerous buildings around the world with large green wall installations.
- The system for constructing a green wall consists of a framework that can be attached to the wall with containers or pockets for the plants and an automatic watering system that also provides nutrients.
- Interior landscaping (green walls) have been shown to improve air quality in building by utilising C02 and giving off oxygen.
- They can also increase the humidity as they lose water by transpiration through their leaves.
- In hospitals. they can speed patient recovery and in offices employees report greater job satisfaction.
- They can also help to absorb noise creating a more peaceful working environment.
- Vegetable production (tomatoes) rockwool slabs are a very successful way of growing commercial crops such as tomatoes.
- Glass houses provide ability to produce crops in areas without soil.
- Temperature is indifferent to seasonal changes so crops can be produced year round.
4.3 Identify the environmental implications of growing plants in water culture.
- The rock wool system creates a lot of difficult to dispose of waste e.g. rock wool blocks
- Water pumps use a lot of electricity
- Hydroponics uses less land
- Uses less water than traditional soil growing
- Has a reduced need of pesticides
