2. Learning outcomes
• 2.4 State the purposes of primary and secondary soil
cultivations, including the addition of soil conditioners.
• 3.1 Explain what is meant by ‘soil texture’.
• 3.2 Describe the physical characteristics of the soil
particles sand, silt and clay.
• 3.3 Describe how the characteristics of each of the
soil particles listed in 3.2 affect soils and their
suitability for horticultural use.
• 3.4 Explain what is meant by ‘soil structure’ (soil
aggregates) and state how root establishment and
growth are affected by different soil structures.
• 3.5 State that a crumb soil is the ideal structure for
horticultural use.
3. Soil Texture - definition
Soil texture is the percentage of sand,
silt and clay in a particular soil
Soil texture cannot be permanently
changed.
7. Big particles, Small particles,
small surface area. enormous surface
area.
8.
9. Soil Structure
Soil structure is the way in which soil
particles are arranged into aggregates
and the aggregates relate to each
other
10. Soil structure stability
Clay and humus act like glue in soil aggregates
containing larger particles making them stable.
However soils with high clay content may not be
stable. The aggregates will break down if
compressed when wet. This leaves a solid mass.
May form large blocky or column- like aggregates.
Sandy soils with low levels of clay or humus are
unstable; the aggregates break down easily into
their component particles under compression or
cultivation.
11. Characteristics of soil types
Clay soils Warm slowly and cool slowly. High CEC so fertile.
Retain high levels of water which can lead to
working and drainage problems.
Silt soils Good water retention. Can be fertile. Easier to
work. Unstable soil structure can lead to capping
and water logging.
Sandy soils Quick to warm and cool. Drain freely, which
makes them easy to work, but also prone to
drought. Organic matter breaks down quickly.
Very sandy soils can have unstable structures.
Nutrients leach out as no CEC.
Loam The best of all worlds. Structure is easily worked
into crumb aggregates. Good CEC combined with
good drainage and water holding capacity. Easy
to work.
12. Soil structure impact on
plants
Sandy soils – large pores (lots of air, little water),
weak aggregates, no nutrient retention (CEC)
which may limit growth if not
supplemented/irrigated. Easy for roots to
penetrate.
Clay soils – small pores (lots of water, less air),
may form very large aggregates, good CEC.
Fertile so good growth. May be hard for roots to
penetrate. Lack of air in soil may lead to root
death if waterlogged.
Loam soils – mix of pore sizes (holding both water
and air), stable small/medium sized aggregates,
some CEC so good growth, good root penetration.
13. Cultivation types
Primary cultivation – digging (single or
double), ploughing or rotavating.
Aerates the soil; incorporates organic
matter; buries weeds and crop waste;
exposes pests and allows weathering.
Starts to break down large aggregates
14. Cultivation types
Secondary cultivation. Includes forking
over, raking, treading to firm the soil and
harrowing. Done after primary cultivation.
Produces a fine crumb-like structure
Firming allows good rooting by reducing
large voids in the soil into which roots may
grow and die off.
Levelling prevents run off of water and
therefore erosion of fine soil particles.
To incorporate dry power or granular
fertilizers evenly into the soil by raking.
15. Learning outcomes
• 2.4 State the purposes of primary and secondary soil
cultivations, including the addition of soil conditioners.
• 3.1 Explain what is meant by ‘soil texture’.
• 3.2 Describe the physical characteristics of the soil
particles sand, silt and clay.
• 3.3 Describe how the characteristics of each of the
soil particles listed in 3.2 affect soils and their
suitability for horticultural use.
• 3.4 Explain what is meant by ‘soil structure’ (soil
aggregates) and state how root establishment and
growth are affected by different soil structures.
• 3.5 State that a crumb soil is the ideal structure for
horticultural use.
