Distinguish between soil texture and soil structure:
Soil texture
- Refers to the coarseness or finess of soil particles when rubbed between the fingers.
Soil structure
- Refers to the way in which individual soil particles (aggregates) are arranged in relation to one another.
OR
- Refers to the way in which soil particles stick together.
Soil structures (clay, sand & loam)
Clay soil
- Particles in clay soil stick together very easily and therefor clay soil has a strong structure.
Sand soil
- In sand soil particles do not stick together and sand soil is therefor called structure less
Loam soil
A loam soil has a crumb structure as some of the particles stick together and some are loose
Describe soil texture in terms of different soil particles
Sand – has large particles and thus has a coarse texture.
Silt – has small particles but not as small as clay and thus have a fine texture.
Clay – has the smallest soil particles that have a smooth feeling and thus a fine texture
Classifying of soil particles according to its diameter.
Gravel – greater than 2mm in diameter.
Coarse sand – 2mm-0.2mm in diameter.
Fine sand – 0.2mm-0.02mm in diameter.
Silt – 0.02mm-0.002m in diameter
Clay – below 0.002mm in diameter.
Ways to determine soil structure
- Rubbing test
- Sausage test
- Settling test
- Nest sieve test.
Explain what is meant by a soil crumb:
Soil crumb
– is the state of the soil in which the individual particles aggregates form crumbs.
- Are formed when loose particles stick together because of organic material.
Explain what is meant by a soil crumb structure:
Crumb structure
– refers to the soil particles which are aggregated into crumbs to allow air and water to penetrate easily.
OR
- Soil particles are bounded together and yet allow air and water to circulate freely.
How crumb structures are formed
- By adding organic matter or manure to sandy soil
- By adding lime to clay soil to the particulars into crumbs.
How crumb structures are formed
- By adding organic matter or manure to sandy soil
- By adding lime to clay soil to the particulars into crumbs.
Importance of maintaining a good crumb structure
- Improves aeration
- It improves drainage to prevent water-logging
- It improves water holding capacity
Describe the components of different types of soil
- 45% mineral particles
- 25% water
- 5% organic matter
- 25% air
Inorganic matter/mineral particles
- Soil originates from rock weathering
- It is the largest component of soil which makes up 45%
Air
- Found in the pores between the soil particles
- It is important for respiration of micro-organisms and plant roots.
- It makes up 25%
Water
- Helps dissolve plant nutrients before they can be absorbed by plants
- Living organisms in the soil also need water
It makes up 25% of the soil
Organic matter
- This are dead and decomposed plant and animal materials
- Adds fertility to the soil
- It improves water holding capacity
Describe the major functions of the following plant nutrients
Nitrogen (N)
- Promotes vegetative growth e.g. stem and leaves
- For the formation of chlorophyll that gives plant leaves green colour
Deficiency in nitrogen on plants
- Poor growth rate (stunted growth)
- Leaves turn yellow (leaf chlorosis)
Organic sources
- Compost
- Manure
Inorganic sources
- NPK fertilizers
- Urea
- Ammonium nitrate
