Barrons AP Environmental Science

substance that remains after most of the organic litter has decomposed is called
humus. Earthworms often help mix humus with minerals in the soil. Soil
containing humus will crumble, allowing air and water to move easily through
the loose soil, making root growth easier, reducing erosion, and stabilizing the
pH.

Soil Quality

Soil quality reflects biodiversity and productivity. Components of soil quality are
listed in the table below.

Components  of  Soil    Quality

Component Role  in  Determining Soil    Quality

Aeration Refers to  how well    a   soil    is  able    to  absorb

oxygen, water,  and nutrients.  Aeration,   which

reduces soil    compaction, involves    perforating the

soil    with    small   holes   to  allow   air (especially

oxygen),    water,  and nutrients   to  penetrate   to  the

roots.  This    helps   the roots   grow    deeply  and

produce a   stronger,   more    vigorous    plant.  When

there’s little  or  no  light,  plants  require oxygen  to

break   down    the plant’s sugar(s)    to  release CO 2 ,

water,  and energy.

Degree  of  soil

compaction

Heavily compacted   soils   contain few large   pores

and have    a   reduced rate    of  both    water   infiltration

and drainage    from    the compacted   layer.

Nutrient-holding

capacity

The ability of  soil    to  absorb  and retain  nutrients

so  they    will    be  available   to  the roots   of  plants.

The process of  weathering  greatly influences  the

availability    of  plant   nutrients.  Initially,  as  soil

particles   begin   to  weather,    primary minerals

release nutrients   into    the soil.   As  these   particles

decrease    in  size,   the soil    is  also    able    to  retain

greater amounts of  nutrients.  The capacity    to

hold    and retain  nutrients   is  greatly reduced in

highly  weathered   soils   since   most    nutrients   have

been    lost    due to  leaching.   Primary plant   nutrients

are nitrogen,   phosphorus, and potassium.