Lecture #8 Soil-Water-Plant Flashcards
Sandy soils:
Clay Soils:
Humus:
- Large soil particles and pores
- Fine soil particles and pores
- binds soil particles into large aggregates, gives structure
Gravitational Water
all water that can freely drain under gravity in the soil
Capillary Water
Water held by capillary forces withing soil pores against gravity, beneficially stored within rootzone for plant use
clay soil 40% retention
sand soil <15%
Hygrosopic
water bound to soil particles by adhesion, not ready for plant use, clay soils have more
Positive pressure potential
when watertable is above location the water is under positive pressure
Negative potential/ tension/ capillary pressure
watertable below location
How is capillary pressure caused
by presence of menisci ie. air-water interface
surface tension of water works to minimize sureface area of interface
How does capillary pressure affect plants
water released to roots and remaining water recess into smaller pores to reduce surface area
as radius of curvature decreases, capillary pressure increases (becomes more negative)
the smaller the pores, more negative capillary gets and greater effort by plant roots to get water
How does water move through soils
moves as “bulk flow”
moves from high water potential to low water potential
governed by darcys law
capillary barrier
when soil becomes more dry, the K (permeability) drops rapidly until reaching capillary barrier
it is a layer of dry soil that does not permit water to enter under unsaturated conditions
where does water mostly enter roots
near the root tip
What are root hairs
hairs on root that help increase contact area
Suberization
when mature parts of plants become impervious to water
helps draw water from new roots further from base of plant
3 pathways of water flow in roots
apoplast
symplast
transmembrane
Apoplast
non plastic, include cell walls and intercellular material
water does not cross any plasma membranes and it is mainly an exo-cellular pathway (goes around cells)
