Soil Water Original by Casey Osksa Modified by Georgia Agricultural Education Curriculum Office July, 2002

How much Nitrogen is in the Air above one acre? There are 69,155,856 pounds of nitrogen in the air above an acre.

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

What are the water requirements for plants? plants use several hundred pounds of water for each pound of dry matter produced

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 clay pores swell shut when they get wet

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

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

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

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

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)

What is Field Capacity? when the soil contains the maximum amount of available water, the greatest amount of water it can hold against gravity

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

What is Available Water? the amount of water between field capacity and wilting point

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

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

How is soil moisture measured? soil is weighed dry, then wet (expressed as a percent of dry wt) electrical conductivity

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

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

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

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.