Particles, Structures and Water Flashcards
What is soil texture based on?
Proportion of sand, silt and clays
Example of soil texture…
10% clay, 60% silt and 30% sand being sandy loam
Example of soil porosity…
Clay gaps small whilst sand large
What does porosity influecenc?
Drainage and water retainment
What does texture influence?
Soil fertility based on storage and plant nutrient supply
Soil Structure
Refers to sand/silt/clay bonded into aggreagets
How does aggregation occur?
Formation then stabilisation, formation by shrinking/swelling of soil by freezing or root penetration breaking soils into discrete units
Types of aggregate?
Microaggregates (<250micrometres) (Macroaggregates(>250micrometres_
Microaggregates formation…
First clay flocculation where clay paritcles conglomerate
What enhances microaggreagate microbial adegradation?
Organic matter association
What does macroaggregates derive from?
Microaggregate coalescing
What does stability depend on in low clay concentration?
OM
What does stabilising OM consist of?
Plant by-products like polysaccharide glue and the other and roots and fungal hyphae
How is pore and aggregate arrangement altered?
Tillage, plant roots and swelling
How can pore space be calculated?
Rastio of weight to volume, as greater amount of soil particles with least amount of pore space weighs more3
Why is pore size important?
Determine retention, larger pores holding water more loosley whilst smaller more tightly
How is bulk density measured?
Mass of soil divided by volume of a cylinder
Three pore classificaitons?
Macropores
Mesopores
Micropores
What is soil moisture characterisitcs determined by?
Composition of pores
Hyrdrualic Conducitivty
How easily water can move through profile, determining wetting front
Wetting Front
Water infiltration moving down the profile
What does HC depend on?
Water flow resistance by soil particles
Pressure generated by water in soil
What is pressure a function of?
Elevation and pressure generation of overlying water columb
What is pore resistance to water flow?
Determined by how well pores are connected, pore-size distribution and water ocntent of the soil
Darcy Law
Refers to discharge being proportional to the loss
Field Capacity
Emptying of macropores where remaining water held is within meso/micropores
Why is aggregation important?
Allows withstanding slaking and compaction preventing poor water infiltration and gas exchange
Where is aggregate instability most present?
Sand and silt
Soil crusting
Where aggregates release into soil pores, preventing further water infilitration
Why might water tension be bad?
Limit nutrient uptake due to the energy required to extract them
What does pore size distribution determine?
Plant-availabe wateM
Moisture Release Curve
Gives water content against water tension
Why shouuld large and small pores be balanced?
Gas exchange and water storage
What are the best agriculture soils?
Loamy textures with equal silt, clay and sand for enough water for plant growht and pores for gas exchange
