Chapter 11 Soil: Foundation for Land Ecosystems

A loam soil is a mixture of

40 percent sand, 40 percent silt, and 20 percent clay.

Most plants grow best when the pH value of the soil is at or near

6.0.

Topsoil, the layer of soil composed of mineral soil particles mixed with humus, is found in the

A horizon.

17) In a temperate deciduous forest, which soil horizon contains the leaf litter, twigs, seeds, and humus of the forest surface?

O horizon.

Humus is (or refers to)

a residue of organic matter that remains after most of the rotting and decomposition has occurred.

Of the following choices, the smallest-sized soil particles are

clay.

The nutrients supporting the lush growth in tropical rainforests are provided by

decaying biomass on the forest floor.

31) Sheet erosion occurs as a result of:

decreased infiltration and increased runoff.

The process of soil being washed or blown away is called

erosion.

Which of the following soil conservation methods would reduce losses due to wind erosion?

establishment of shelterbelts.

Which of the following would produce the least amount of sediments that could enter bodies of water?

forested areas.

Which of the following is a characteristic of sandy soils?

good drainage but poor water retention.

As far as agricultural applications are concerned, the main distinction between topsoil and the underlying subsoil is that topsoil

has a higher humus content.

33) Deforestation is more damaging to tropical soils than temperate zone soils because:

high rainfall, uniform warm temperatures and rates of decomposition cause rapid loss of humus.

4) Nutrient-holding capacity of the soil is a measure of

how readily nutrients may be leached from the soil.

The spongy, dark brown or black material that remains from a rotting dead log is called

humus.

The process of water soaking into soil is known as

infiltration.

The aspect of a soil which determines its fertility is

ion exchange capacity.

Some forest plants can obtain nutrients from a symbiotic association with:

mycorrhizal fungi.

A method of agriculture that reduces soil disturbance from cultivation is

no-till planting.

A soil that allows very little leaching has good

nutrient-holding capacity.

Leaching is a term that refers to

nutrients or other chemicals being removed from the soil by water percolating through the soil.

Soil texture is a measurement of the

proportion of sand, silt, and clay-sized particles.

Which of the following would result from soil compaction?

reduced infiltration of water.

Which of the following is an effect of plant cover?

reduction in wind and water erosion.

11) Which of the following is a symbiotic relationship found in soils?

roots of certain plants and fungi.

When soils that lack adequate subsurface drainage are heavily irrigated the

salinity increases.

Leaf litter on a forest floor helps protect underlying soils from

splash erosion.

The best agricultural soils in the world are:

temperate grassland soils (mollisols)

Mineralization of a type of soil refers to

the loss of its humus content through oxidation

Most land plants require substantial quantities of water to replace water lost through

transpiration.

The major source of minerals that cause soil salinization is:

use of irrigation water containing dissolved salts.

The gradual breakdown of rock into soil particles by physical and chemical processes is called

weathering.