lecture 10 Flashcards
how are soils grouped into textural classes?
based on % of sand, silt, and clay
* At each point it is 100% of one type/soil kind
Loam - middle area
how is soil structured? look at diagram
- Aggregation of mineral particles with Organic Matter into larger units
- Glue that holds aggregates together = OM and clay
- Pores= spaces between aggregates
Always has air bc particles don’t fit perfectly together
describe porosity
Pores contain and affect water and air movement
* Size of pores and total pore space - influenced by soil texture
coarse (sandy) soil pores?
- Coarse texture (sandy) soils have:
○ Larger pores but less total pore space
Affects water infiltration and percolation, well aerated
Fine textured (clay) soils pores?
- Fine textured (clay) soils have
○ Smaller pores but more total more space
Affect h2o infiltration and percolation, tend to waterlog
what is permeability? how does it differ for clay vs sandy loam
- Permeability - how fast air and water moves through soil
- Clay loam - takes longer and half the depth of sandy loam
Matters for the availability of water for organisms - if the drainage or retention of moisture is useful or not
- Clay loam - takes longer and half the depth of sandy loam
describe soil water - saturated, field capacity, unsaturated
- Saturated soil - pores are full of water, water drains under the influence of gravity (saturated flow)
- Once all gravitational water has left the soil, the soil is at field capacity (no more free drainage)
Unsaturated floe will continue (e.g through the roots) until wilting point - water is held too tightly by soil particles to be removed by plant
- Once all gravitational water has left the soil, the soil is at field capacity (no more free drainage)
water holding capacity factors? (3)
- Field capacity - enhanced by clay - large pore volume and surface area
- Measure by drying soil and weighing
- PWP - also increases wih more clay
- Water available for plant use = difference between water at field capacity and PWP
- Part of why loam soils are good for growing
- Organic content of soils Functions
○ Important as a nutrient source
○ Holds water (much like clay) ;impacts on field capacity and wilting point
○ Contributes to aggregation, cation exchange capacity (CEC)
○ Energy for soil microorganisms -decomp
Mycorrhizae - fungi that form symbiosis with plants increasing plant water and nutrient absorption
how are the chemical properties of soil neceessary - what does composotion vary with?
- Soil solution= soup of dissolved chemicals available for plants and soil organisms; contrains ions
- Composition varies with time + depth
○ Cations (+) = AL3, NH4,K,MG2,CA2
○ Anions (-) = CL-, NO3, SO4 2 . HCO3
- Composition varies with time + depth
inputs and depletions of chemicals in soil?
- Inputs: from atmosphere, transformations
Depletions - through plant uptake, transformations to solids, losses from ecosystems
what is CEC? what does it indicate? when is it high
*
* Cation exchange capacity
Ability of the soil to hold onto nutrients (cations) for plant use and prevent leaching ebyond roots
* Good indicatior of soil fertility, quality, productivity
Clay and humus (OM) - begatively charged (higher CEC)
what is CEC influenced by?
○ Soil texture CEC (high number = more cations held)
§
○ Strength of absorption - the strength of the bond of the cations
○
○ The relative concentration of cations in the soil solution
CEC levels of different soil types
Sands (light-colored) 3-5
Sands (dark-colored) 10-20
Loams & silt loams 10-25
Clay and clay loams 20-50
Organic soils 50-100
strength of cation bonds from strong to weak
Al+3 >
H+
Ca2+ >
Mg2+ >
K+=NH4+
Na
