A combination of cool, wet weather in early spring and
planting in reduced-tillage or no-till fields reduces the amount of sulfur and
nitrogen that is released in the soil by decomposition and mineralization of
organic matter, particularly in northern regions of the U.S. Recent changes to sulfur emission regulations
have decreased the amounts of sulfur that is deposited to the soil through
atmospheric channels. Field studies were
conducted in 2005 at six corn (Zea mays L.) sites in Michigan to evaluate the effects of sulfur
starter fertilizer on nutrient uptake, plant growth, and grain yield. Four sites were on-farm strip trials with
treatments of ammonium sulfate (21-0-0-24S) band-applied at planting at rates
of 0, 5.6, 11.2, and 22.4 kg S ha-1.
Two other sites on university research farms included additional starter
fertilizer treatments of 28 kg N ha-1, 28 kg N ha-1 + 28
kg P2O5 ha-1,
28 kg N ha-1 + 28 kg P2O5 ha-1
+ 11.2 kg S ha-1, and 11.2 kg S ha-1 as gypsum (16%
S). Grain yield responded positively to
the 22.4 kg S ha-1 application at two of the six sites in the study,
with an average of 16.4 Mg ha-1 increase in grain yield over the
control (0 kg S ha-1). One
site showed a negative response (yield) to the 22.4 kg S ha-1
treatment, likely due to salt toxicity stemming from fertilizer being placed
directly below the seed. No yield
differences were observed among any of the other starter treatments at any of
the locations. Responses observed in
plant tissue S content and grain yield at the strip trial sites may be
attributed to nitrogen rather than sulfur.
When sulfur was applied as gypsum, there was no yield difference
compared with the control plots.