soil water

soil water

the most limiting factor in crop production, on average crop plants use 500-700 pounds of water for 1 pound of dry plant matter

why do plants need water

turgor pressure (keeping plants stiff), used in plant photosynthesis, transpiration (cooling), soil water has dissolved nutrients in it and carry nutrients around plants

forces on soil water

gravity, adhesion, and cohesion (work against gravity)

cohesion

the attraction of water molecules to each other

adhesion

attraction of water to other charged particles

soil water potential

a concept used to measure soil forces- the work that water can do when it moves from its present form to a pool of water in a defined reference state, how much work a given amount of water can do, always trying to achieve a lower energy state, expressed as a negative number, the more negative the number the more work must be done to move the water, standing water is 0

plant water absorbtion

plants absorb water from the film surrounding soil particles, regulated by soil water potential

matric potential (force)

always zero or less (absorbed water has less ability to do work), responsible for adsorption and capillary action

gravitational potential force

water is above the water table thus carries potential energy from gravity

osmotic force potential

attraction of ions and other solutes from water (cohesion) water geos to the area with higher concentration of dissolved solids or where there is less water

how roots get water

as water is taken from the soil the water potential closer to the root is reduced, capillary flow carries water from higher potential areas towards the root

capillaries

small tubes where fluid can move against the force of gravity

field capacity

the point where excess water has completed draining, water is held against gravitational force

gravitational water

extra water that drains through the profile generally between 24-48 hours

permanent wilting point

plants cant take up water, unable to overcome soil water potential

avaliable water

the portion of soil water that can be absorbed by plant roots

hygroscopic water

water that is held so tightly that it can only be removed by drying it in an oven

macropores

enable water and air to penetrate rapidly and deeply, earthworm burrows

mesopores

important for intense renewal of air and transportation/distribution of water, eventually pulled down by gravity

micropores

important as a reservoir for plants and microorganisms, water held at field capacity

water movement and soil texture

clay holds water and lets its spread outward through the horizon while coarse textured soil drain water strait down

clay on sand texture and water

when clay is over sand the clay hold onto water against gravity as sand has no capillary abilities, when enough water accumulates in surface clay it loosesns its hold freeing the water to move down

patter of removal (roots)

caplillary water flow cannot supply all the water that plants need, roots grow best where there is oxygen and water (near the surface) and roots must spread out to get water

sand on clay water effects

whent he coarser texture is above a finer texture, the finer soil pulls water down at a slower rate so water builds up above the fine textured soil

sharp boundry between soils

can be helpful by making surface soil retain more water but can injure roots is the soil is too wet, as moisture is removed water need to be taken from deeper in the soil and when the spring is wat that can keep roots to shallow for adequate anchorage and water shortage