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Soil Moisture Behavior

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Why is water important to plants? it is a nutrient serves as a solvent for other nutrients

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What are the water requirements for plants? plants use several hundred pounds of water

for each pound of dry matter produced

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How does water enter the soil?

through pores in the soil sandy soils have the largest pores, but are

often filled with other material medium textured soils (loamy) have good

water entry properties clays, pores swell shut when they get wet

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What is Adhesion?

it is the attraction of two different molecules (water to soil)

Water held by adhesion = not available to the plant

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What is Cohesion?

it is the attraction of two similar molecules (water to water)

Water held by cohesion = IS available to plant

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What is the importance of adhesion and cohesion in soils?

water molecules are strongly attracted to soil minerals and organic materials due to adhesion

water molecules are also strongly attracted to each other due to cohesion

soil holds a thin layer of water, that layer holds a thin layer of water etc., the farther away from the soil particle you get, the looser the water is held

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What is the importance of adhesion and cohesion in soils? water then tends to move from wetter places

to drier places. Roots remove water, then water is drawn from surrounding areas

in dry conditions, water moves slowly and only fractions of an inch, thus roots must be well distributed

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How is soil water classified?

1) Hygroscopic Water is held so strongly by the soil particles (adhesion), that it is not available to the plants

2) Capillary Water is held by cohesive forces greater than gravity and is available to plants

3) Gravitational Water is that water which cannot be held against gravity as water is pulled down through the soil, nutrients

are"leached" out of the soil (nitrogen)

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What is Field Capacity?

when the soil contains the maximum amount of available water, the greatest amount of water it can hold against gravity

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What is Wilting Point?

the soil has so little water, that plants can no longer recover from wilting

roots can no longer take in water

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What is Available Water?

the amount of water between field capacity and wilting point

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What is Water Table?

the level beneath the soil which the soil is saturated with water

marshes develop where the water table is just below the ground surface

if the water table is not too low, dryness tends to correct itself through capillary movement

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What is saturation?

When all pore spaces are filled with water Unhealthy state for plants when prolonged

because the oxygen dissolved in the water that is needed for respiration is quickly utilized

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What affect does soil particle size have on its water holding ability? the smaller the individual particles are, the

more surface area there is, thus it will hold more water

consider a book compared to all of its pages

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How is soil moisture measured? soil is weighed dry, then wet (expressed as a

percent of dry wt) electrical conductivity

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What factors determine the amount of soil moisture?

amount of snow, rain, irrigation rate which soil permits water entry water storage capacity of soil evaporation rate height of water table rate which water can move within the soil amount and type of vegetation

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How can we increase the amount of available water to the plant? Precipitation: better utilize snow and rain by

keeping the water on the soil surface. windbreaks keep snow in place (cover) strip cropping contour strips grassland farming

Irrigation: may not be practical Water entry: reduce cultivation, green

manures, correct alkaline soils

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How can we increase the amount of available water to the plant? Storage capacity: increase O.M.

(manures) Evaporation: conservation tillage,

shelter belts, strip cropping Water movement in soil: O.M. Vegetative covering: holds water

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How much water do plants need?

Transpiration Ratio: pounds of water to produce a pound of dry matter.

Corn = 350# Wheat = 500# Potato = 630# Grass & Alfalfa = 860#

It takes 4,533 gallons of water to produce enough food for one person for 3 meals. (That's 1,654,545 gallons per year)

It takes 10,000 gallons of water to make one bushel of wheat

It takes 7.35" of rain to make a 20 bushel per acre crop.