RHS Level 2 Certificate

Year 2 Week 2 – Soil Texture, Structure and Cultivation

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.

Soil Texture - definition

Soil texture is the percentage of sand, silt and clay in a particular soil

Soil texture cannot be permanently changed.

Soil particle sizes

Soil ParticlesSoil minerals exist as sand, silt and clay particles.

Sand particles are big. Clay particles are small.

Sand: big particles,

big pores.Clay: little

particles, tiny pores.

Small particles,

enormous surface area.

Big particles,

small surface area.

Soil Structure

Soil structure is the way in which soil particles are arranged into aggregates and the aggregates relate to each other

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.

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.

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.

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

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.

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.