Exam 3

Which of the following accurately describes a characteristic of the water molecule? A. The H to O to H angle is approximately 90o C. B. The two H atoms are on diametrically opposite ends of the molecule. C. It has a positive and a negative side. D. It is attracted to surfaces with negative but not positive charges. E. It is held in soils by adhesion but not adsorption.

Capillarity in soils _____. A. involves both adhesion and cohesion B. is enhanced by the symmetrical nature of the water molecule C. is independent of the matric potential in soils D. is not involved in the process of water uptake from soils E. does not account for unsaturated water movement in soils

Two soil samples, A & B, at different soil moisture levels are placed in contact with each other. Water will more likely move from soil A to soil B if their water potentials, expressed in kPa, are: A. A=-5; B=+5 B. A=-5; B=-5 C. A=-20; B=-10 D. A=-30; B=-40 E. A=-100; B=-50

The osmotic potential would likely be lowest in soils of which of the following orders A. Aridisols B. Histosols C. Oxisols D. Ultisols E. Spodosols

The matric potential of soil water is _____. A. influenced greatly by the content of salts in the soil B. not influenced appreciably by the force of gravity C. is generally higher than that of pure water outside the soil D. is little affected by soil solids E. is lower in a sandy soil with 20 percent soil water than in a clay soil with same percentage of moisture

Which of the following best characterizes the field capacity of a soil? A. maximum capacity of a soil to hold water B. water content of a soil with water potential of about -10 kPa C. the total capillary water in a soil D. a wetted soil prior to the removal of the gravitational water E. soil with water potential of -1500 kPa

Which of the following means of estimating soil water levels gives a direct measurement of the water content? A. gypsum blocks B. neutron scattering C. gravimetric determinations D. tensiometer E. pressure membrane

Unsaturated water flow _____________. A. is faster than saturated flow B. is driven primarily by the force of gravity C. is stimulated by the osmotic potential D. is slower on sands than on clays if the soil moisture content is high E. occurs on soils that are at field capacity

In which of the following situations would you expect downward movement of soil water through the profile to be most rapid? A. uniformly textured sandy loam profile B. sandy loam in upper layers with a clay band underneath C. sandy loam in upper layers with a layer of coarse gravel underneath D. clay texture throughout the profile E. silt loam in upper layers underlain by a sandy layer

At which of the following soil moisture potentials (expressed as kPa) is the soil water held most tightly? A. +5 B. 0 C. -31 D. -1500 E. -3100

At which of the following soil moisture potentials (expressed as kPa) is the waters’ energy level lowest? A. +5 B. 0 C. -31 D. -1500 E. -3100

Soils high in organic matter commonly hold more available water than comparable soils with lower organic matter levels. This is most likely due to what characteristics of the high O.M. soils A. larger micro pore space B. lower permanent wilting percentage C. higher field capacity D. higher capacity of the O.M. to hold water tightly E. higher clay content

In which of the following “forms” of soil water are pesticides, excess plant nutrients and waste chemicals most apt to move through soils? A. gravitational B. unsaturated C. available D. hygroscopic E. capillary

Which of the following statements concerning applications or capabilities of soil moisture measuring devices is (are) true for the use of a drying oven and balance? A. requires “destructive sampling” for each measurement B. good to turn on automatic irrigation at -5.0 kPa C. used to turn on irrigation when soil moisture potential reaches -20.0 kPa D. gives same reading for loamy sand and silt loam if both contained 15% moisture E. both A and D

The expression, P - ET -SS estimates the ________ a watershed. A. soil water content of B. discharge volume from C. evaporation from D. interception in

The water potential at the leaf surfaces expressed in kPa is most likely to be _____. A. -10 B. 33 C. -33 D. -500 E. -31,000

Plant transpiration efficiency at a given location is markedly influenced by _____. A. organic residue cover on the soil B. tillage practices used C. fertilization practices used D. the plant species being grown E. both C and D

Which of the following will increase the evaporation (E) from the soil surface? A. adding straw mulch to the soil surface B. the use of no-till culture C. stubble mulch farming D. plastic mulch E. none of the above

Which of the following locations in the United States would have the highest evaporation (E) from the soil surface in July? A. a bare, unirrigated dry land soil in Colorado B. an unirrigated soil in South Carolina growing cotton C. a furrow-irrigated cotton field in Arizona D. a forest woodland in Illinois E. a corn field in New York

Urban development of land under natural vegetation or agriculture usually greatly _____ soil infiltration capacity and therefore greatly increases _______. A. decreases …… stream bank erosion. B. increases …… stream bank erosion. C. decreases …… groundwater recharge. D. increases …….groundwater recharge.

The likelihood of polluting groundwater with pesticides and plant nutrients is enhanced by _____. A. the presence of macropores in the soil B. light tillage of the upper centimeter or so of soil C. the use of tillage to control weeds D. the production of oats rather than wheat E. conventional tillage as a choice compared with conservation tillage

Which of the following irrigation systems produces the most biomass per unit of water applied? A. flood irrigation B. furrow irrigation C. drip irrigation D. sprinkle irrigation E. furrow-dike irrigation

Groundwater _____. A. is a source of water above the vadose zone in a soil B. moves downward in the vadose zone through the capillary fringe C. moves laterally but not vertically below the soil profile D. is found mostly in shallow layers just below the argillic E. is a major source of water for irrigation in the United States

Land drainage is beneficial because _____. A. it increases the alternate of expansion and contraction due to freezing and thawing of soils B. it increases the water-to-air ratio in the soil pores C. it slows down the rate of soil warming in the spring D. it increases the depth of root penetration in the soil E. it increases the availability of iron and manganese in acid soils