important as the primary nutrients but taken up in smaller quantities.
as much attention is given to adding these nutrients to the soil
because they are added incidentally.
the pH is raised by liming Ca is added to the soil. Mg is
added when dolomitic limestone is used.
sulfur is replenished by sulfur dioxide from the air brought
down by precipitation. Regulations on air pollution have
reduced this in recent years. Added incidentally with other
fertilizers ordinary superphosphate.
Form used by plants
by plants as the Ca2+ from exchange sites or soil
in rocks and minerals from which the soil is formed - dolomite,
calcite, apatite, calcium feldspars.
humid regions even soils formed from limestone are acid in
the surface layer because Ca2+ may be removed by
excessive leaching. H2O + CO2 ===>
H2CO3 Carbonic acid
Calcium added to Soil
used to improve acid soils add Ca
is used to supply Ca without changing the pH.
Behavior of calcium in the soil
is dependent on the percent of the cation exchange complex
occupied by Ca2+ rather than the absolute amount.
a. Kaolitic clays (1-1) can supply enough Ca to plants at saturation
values of 40-50?
b. Montmorillonitic clays require Ca situation of 70% to supply
Forms compounds that a part of the cell walls -- to strengthen
Stimulate root growth and leaf development.
Calcium is very immoble in the plant. Ca in the leaves is
not translocated to the fruit. The Ca must be supplied by
the soil when the fruit is forming.
Ca deficiencies can occur in the fruit when soil moisture
is low. ex. blossom
end rot of tomatoes.
Ca is required for good peg development. Since Ca is immoble
in the plant, gypsum is broadcast at the rate of 1000 to 2000 lbs./acre on the soil surface to insure
Gypsum is applied at the time of blooming so that Ca is available when pegging begins.
Gypsum sources: Mining, Byproduct, recycling
Ca is required for the rhizobia to form nodules on the roots.
taken up by plants Mg2+
olivine, biotite mica the minerals containing magnesium are
easily weathered. The soil is depleted of weatherable Mg minerals
relatively sooner than most Ca, Mg and K minerals.
Mg2+ is the largest source of plant available Mg.
to 18% of exchangables bases are usually Mg2+ ions compared
to 75-85% for Ca.
Mg2+ hydrates to form a larger ion than Ca therefore,
it is adsorbed less strongly by the cation exchange complex.
is excessive if it occupies more than 40-60% of CEC deficient
if less than 3-8%
adsorption of these double charged ions results in a lower percentage
in soil solution than other cations like K and Na.
K fertilization can induce Mg deficiency
to photosynthesis -- every chlorophyll molecule contains a Mg
deficiency causes grass tetany in ruminants
and tobacco are particularly sensitive to Mg deficiency
drown of tobacco
salts MgSO4 is a fertilizer source other than dolomitic
Form utilized by the plant : absorbed by plants as SO42-
anion small amount through leaves as SO2
found in soil solution as the SO42-.
Negative charge so there is little adsorption on clays. Moves
with the soil water and is easily leached.
organic matter is the source of soil sulfur. N-S ratio 10-1
Sources of sulfur added to the soil.
atmosphere - (SO2) sulfur dioxidebrought down by
ordinary superphosphate 9-12% S
gypsum - soluble - neutral in reaction 17% S copper sulfate
elemental Sulfur - when added to soil it is oxidized to H2SO4
by microorganisms very acid. 300 lbs./acre would require 1000
lbs. of CaCO3 to neutralize.
Sulfate movement and retention
reacts with the same anion exchange sites as H2PO4-,
HPO42- is held more strongly
so there is little room for SO42-
on these sites in surface soils.
leaches readily - accumulation in B horizon
Nutrition - part of three amino acids Cystine, Cysteine,
Deficiencies occur on sandy soils low in organic matter in
areas with high rainfall.
symptoms plants show a pale green color
S is part of protein. Plant need a N:S ratio of 15:1
lbs/acre S where leaching is not a problem; 40-60% lbs /
acre an deep sandy soils
Onions-low sulfur soils are needed to grow sweet onions.
Secondary and Micronutrients for Turfgrass