R2102 1.5 The Root Environment Flashcards
What is primary cultivation?
Involves the turning over of the soil
- Single and double digging by hand
- Mechanical ploughing and subsoiling
- Rotovating
What is single digging?
Why do it?
The first operation in the preparation of a seedbed
Mark out a rectangular plot, mentally divide it into two strips, and lift a small trench, 30cm wide, and a spade’s depth, from the end of the first strip. Place this soil to one side, leaving the trench empty. Etc.
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
- Early due to frost action; less beneficial to sandy soils. They are best left until late in the winter or early spring because they have an open soil structure to start with and benefit less from frost action. Also valuable nutrients would be lost from sandy soils if they are dug too early.
- No soil should be dug during frost or when covered with snow as this can harm soil organisms and the soil structure
What is rotary cultivation?
Why do it?
- Can be used for covering larger sites.
- With different attachments they can be used for primary and secondary cultivation.
- Working width of about 50cm and depth of 20cm.
- Basic tines produce different fineness of tilth.
- They reduce the time it takes to cover a large areas. However, they can cause problems in relation to compaction with the creation of soil pans due to cultivation at the same depth (i.e. 20cm).
- Avoid wet or dry conditions to prevent damage to the soil structure.
What are the processes of secondary cultivation?
- Forking – to depth of 10cm
- Raking
Produces a fine tilth suitable for the seed to be sown
The soil must have the correct degree of moisture (not too wet or too dry)
- Hoeing – in dry weather can damage roots of plants
- Consolidation
treading or roller
avoid in wet conditions
Advantages of raised beds?
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
Growing plants in a different soil type
Why add organic matter?
- 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
Why add inorganic materials?
- 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
How is soil structured damaged?
- Cultivating at the wrong time can cause soil structure damage
- Cultivating clay or silt soils can lead to compaction and destroy crumb formation
- Over cultivation such as forking, raking or overuse of mechanical cultivation methods can result in the breakdown of soil aggregates and lead to fine dusty particles and erosion
- Cultivating with rotovators over long periods of time can cause pans to form in the soil
What are soil pans?
- Hard, impervious layers that form as a result of over cultivation with rotovators and/or mechanical methods due to the cultivation at the same depth over extended periods of time.
- Can occur at any level depending on the cultivation method
- Results in damage to the soil structure, water movement is impeded and plant roots are deprived of oxygen
- More common in clay soils or soils that have a poor soil structure
What is surface capping?
- Caused by poor soil structure and lack of pore spaces
- The compaction of the surface layer of soil and is common in soils that have been over cultivated and leads to the destruction of the crumb structure
- Loose, fine particles with low levels of organic matter form a hard, impervious layer, usually after hard rainfall.
- This cap or crust prevents the free movement of air and water and is damaging to plant roots and growth
- It is more common on fine soils after heavy rain, e.g. a recently prepared fine seedbed and there is no surface vegetation
How to avoid or remove compaction?
Addition of organic matter – prevents mineral matter from settling (iron pans) and prevents too much form being washed down into the subsoil
Mulches (e.g. leaf mould) can help prevent surface capping, soil erosion and leaching of nutrients
Green manures
Cultivate at the correct time:
- If too wet then the crumb structure will be destroyed and the soil will become very sticky and form hard lumps when dry; if too dry then cultivation cannot be carried out as the ground is too hard.
- Large lumps or clods can be broken up if the soil is allowed to dry and then rewetted either by irrigation or by rainfall
- Clay is particularly prone to compaction in wet conditions and care must be taken not to cultivate or walk on it in wet conditions
Subsoiling:
- The mechanical method of subsoiling can be used. This involves specific tools that are attachments to tractors or pedestrian operated machines.
- They use a long blade to break down the hard pans.
- They can be used on bare or grassed areas.
How do you identify poor drainage?
Poor plant growth with a sickly appearance and poor yield
Leaves may be yellowish-green and stunted in growth
Moisture-loving plants will indicate marshy conditions. These include plants such as sedges and rushes, Ranunculus flammula (Lesser Spearwort), Stachys palustris (March Woundwort), Potentilla palustris (March Cinquefoil), Hydrocotyle vulgaris (March Pennywort) and Lysimachia vulgaris (Yellow Loosestrife).
There will often be areas of standing water. Water will also run off areas rather than soak into the soil. (Compacted soils will also act in the same way as this layer is impervious to water and it will simply run off.)
The soils will often smell due to the lack of oxygen and the buildup of sulphides within the soil
Bluish/greenish mottled or grey appearance due to the presence of certain iron compounds as insoluble deposits
What causes excess water?
Hard, impervious rock close to the soil surface. This prevents the percolation of water down and causes a high water table.
Compaction will also cause bad drainage either as standing bodies of water or as surface water run-off
Topography can also affect a soil’s ability to drain. Water will often accumulate at the bottom of a slope.
High volumes of run-off water can occur when the is a high presence of impermeable materials such as paving (e.g. patios), tarmac or concrete
How do you get 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. Some types of these drains include a perforated drain pipe (“drain tile”) and may be covered with grass. The traditional French drain is simpler, with no drain pipe and gravel running all the way to its surface.
Raised bed
Appropriate planting – plants that can cope with waterlogged and marginal conditions
The creation of swales and retention ponds (fed by rainwater)
How do you improve soil-moisture content?
• Increase organic-matter content
• Mulching – organic materials or bark chippings
• Wind breaks
• Ground cover planting
