Essential Elements for Plant Growth
Sulfur
Biological functions:
- Amino acids: cysteine, methionine. organic-N/organic-S in plants
typically has a 30-40:1 molar ratio
- coenzymes and prosthetic groups
- glutathionine: antioxidant and precursor to phytochelatins
- alliins in allium (w/ allinase produce pungency in onions) and
glycosinolates in brassica (produces isothiocynates) for chemical
defenses and S storage.
No toxicity to sulfate beyond salinity, S uptake beyond needs stored in
part as sulfate. Deficiency symptoms are yellowing of whole plant,
moderately phloem mobile. Response to S fertilizer in many crops and
regions. With the reduction of sulfur at the smokestacks, agriculture may
be losing the only benefit of acid rain!
Sulfur inputs to soil:
- Precipitation and dry deposition (source: volcanoes, marine aerosols,
coal burning)
- Fertilizers (both intentionally used to fertilize for S and
incidentally contained in N-P-K fertilizers)
Sulfur outputs:
- Crop removal
- Leaching
- (Volatilization)
Soil Testing:
Water extract for sulfate; occasionally use CaCl2 or Ca(H2PO4)2
solutions in order to displace sulfate from anion exchange sites (if
present). Captures existing sulfate levels, but does not account for
sulfate losses due to leaching or accumulation from mineralization of
organic-S.
Sulfur Fertilizers
- Potassium magnesium sulfate, K2SO4.2MgSO4:
22%S
- Sulfur-coated urea: 10-20% S
- Single Superphosphate (13.9%S as gypsum; only 1% S in triple
superphosphate)
- Ammonium sulfate, (NH4)2SO4, 24%
S
- Elemental Sulfur, S (100%S): oxidizes to sulfuric acid, used also as
acidifying agent
- Ammonium thiosulfate (ATS), (NH4)2S2O3,
26% S, 12% N
- Also Al2(SO4)3, and FeSO4,
also used as acidifying agents
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This page was last modified by
Phillip Barak, Univ. of
Wisconsin, on 5 Jan 1999. All rights reserved.