NCSU SSC200 Quiz 5

Conventional Tillage

Destroys surface structure Rapid initial infiltration until surface crusts

Eutrophication is enhanced by the presence of pesticides in the water draining from agricultural soils.

False

Hysteresis is the phenomenon whereby a soil has the same water content/potential relationship when it is being dried as when it is being wetted.

False

Sprinkle irrigation is generally more efficient in the use of water than drip irrigation, especially for high valued crops.

False

The property of cohesion in water stems from the attraction of water molecules for soil solids.

False

3 Soil Water Potential

Gravitational Matric Osmotic

Macropores and Capillary Rise

Gravitational pull is stronger than adhesion so water drains freely

Transpiration

Plants take in water through the roots and release it through the leaves

Drip irrigation would more likely be used in the production of apples or peaches than in the production of wheat.

True

The most important management factors influencing soil aeration in well-drained soils are those that determine the volume of the soil's macropores.

True

The osmotic potential is dependent upon the presence of salts and other solutes in the soil.

True

The polarity of water helps account for the attraction of water molecules for each other.

True

The pollution of ground water is often increased by the presence of macropores in soils.

True

Water molecules have polarity because the electrons are not uniformly shared between the two H atoms and one O atom.

True

Hydrophilic

Water Loving, adhesion and cohesion forces cause the water to "cling" to surfaces.

Dry Soils: Moisture Levels and Soil Water Potential

Water is held tightly by the soil solids Energy status is much lower

Wet Soils: Moisture Levels and Soil Water Potential

Water is loosely held Energy status is relatively high

No-Till

Accumulates organic matter that promotes structural stability Soil structure is not mechanically destroyed

Micropores and Capillary Rise

Adhesion forces is greater than gravity so water will be pulled into the pore

4 Water Properties

Cohesion Adhesion Surface Tension Capillarity

Plant roots obtain access to soil water in which of the following ways? Select one: a. Water vapor moves from the wet soil areas to the root surfaces. b. Roots extend into moist soil area. c. The roots contract and leave room in the pores for the water to move in. d. Water flows to the roots by capillarity. e. both B and D

both B and D

Which of the following processes are most apt to encourage good soil aeration? Select one: a. creation of more macropores b. organic matter decomposition c. root respiration d. reaction of oxygen with organic matter e. diffusion of oxygen from the soil to the atmosphere

creation of more macropores

Positive Potential

energy is stored and can be used for "work"

Negative Potential

energy must be expended to move the water

Soil Water Potential =

gravitational potential + matric potential + osmotic potential

Clay Soils: Moisture Levels and Soil Water Potential

high water holding capacities due to the numerous small pores

Soils high in organic matter commonly hold more plant-available water than comparable soils with lower organic matter levels. This is most likely due to what characteristics of the high O.M. soils?

higher field capacity

Capillarity in soils ________.

involves both adhesion and cohesion

Land drainage is beneficial because ________.

it increases the depth of root penetration in the soil

Sandy Soils: Moisture Levels and Soil Water Potential

low water holding capacity due to fewer micropores

The matric potential of soil water is ________.

not influenced appreciably by the force of gravity

Hydrophobic

soils display resistance to wetting and frequently do not hold water to support good plant growth

Water Repellency

the adhesive forces at the water-solid interface are less than the cohesive force of water

Cohesion

the attraction of water molecules for each other primarily due to hydrogen bonding

Adhesion

the attraction of water molecules for solid surfaces

Evaportranspiration

the cumulative loss of vapor to the atmosphere from evaporation and transpiration

Alternate freezing and thawing of soils results in the "heaving" of plants and the destruction of shallow building foundations. This effect is due primarily to ________.

the expansion of water when it freezes

Capillarity

the movement of water up a wick made of hydrophilic solid material

Which of the following will not increase the efficiency of water use by plants in an irrigation system? Select one: a. the use of flood irrigation for forage crops b. the use of concrete-lined delivery ditches c. the use of crop residues to reduce evaporation d. the use of drip irrigation for fruit trees e. the use of herbicides to control weeds

the use of flood irrigation for forage crops