Download Soils

CRSS 2830
Lesson 6:
Basic Soils
I. SOIL DEFINED
• “That portion of the Earth’s crust that
is made up of mineral materials,
organic matter (living and dead),
water, and air that is capable of
supporting plant growth.”
SOIL DEFINED
• Takes about a 1000 years
for a 6-inch soil layer
to form
II. SOIL TEXTURE
• Mineral portion of soil is made up of
three particle sizes: sand, silt and clay
SOIL TEXTURE
• CHARTS AND GRAPHS
III. SOIL STRUCTURE
• Arrangement of the
mineral particles into
secondary units or
aggregates. Like
crumbs of a cake.
• Size and arrangement of aggregates,
influence pore space.
IV. AIR
• Air fills the soil pore space not filled
with water.
• Oxygen is needed by roots for water
and nutrient uptake. Stay above 10 to
12 %
AIR
• Carbon dioxide at high
levels will impede root
growth above 5%
• Water logged or compacted soils can
result in both limited oxygen and
elevated carbon dioxide
V. WATER
• In between solids, soils
contain pores that are filled
with air or water.(total
porosity).
• Total porosity: sand = 35 - 50%, clay =
40 - 60%. Which drains faster? Why?
WATER
• Pores differ in size. Macropores,
“large” and micropores “small”. Air
fills macropores, water fills
micropores. (mesopores fall between
in size). Ideally want soil at 50% air
and 50% water.
VI. ORGANIC MATTER
• Living: earthworms, gophers,
insects, mice, millipedes, mites,
nematodes, fungi, bacteria, etc.
Important for breakdown of
organic matter to humus
and nutrient release/cycling.
ORGANIC MATTER
• Nonliving: dead plant and animal
residues break down to humus.
Humus has negative charge which
can help adsorb many plant nutrients.
VII.CHEMICAL
PROPERTIES OF SOILS
• Plants are:
– 75 to 85 percent water
– 15 to 25 percent dry matter
CHEMICAL PROPERTIES
OF SOILS
• The dry matter is made up
of 16 essential elements
• Carbon, hydrogen and oxygen come from
air and water. The remaining 13 come
from the soil.
CHEMICAL PROPERTIES
OF SOILS
• Some of the nutrients have
a positive charge
(cations)
• Some have a negative charge
(anions)
CHEMICAL PROPERTIES
OF SOILS
• Clay soils and organic
matter have negative
charges. Therefore, the positive
(cations) are attracted.
• Cation Exchange Capacity (CEC) =
Ability of soil to absorb exchangeable
cations.
VIII. SOIL REACTION (pH)
• pH scale measures acidity or alkalinity:
– Below 7.0 is acid
– Above 7.0 is alkaline
– 7.0 is neutral
SOIL REACTION
• pH of 6.0 to 7.0 is best for
turfgrass growth
• 6.0 to 7.0 is the pH range in
which the essential nutrients are
in available form.