by Jarrod Miller, Extension Specialist - Agronomy
Nitrogen and sulfur deficiencies can both cause a pale yellow color across your hay and pasture fields. Nitrogen deficiencies should start on the older growth first (lower leaves), while sulfur may appear across the whole plant. However, to correct the actual issue, a tissue test will is the best method.
Sulfur leaches easily from the root zone, which is why organic matter is an important sulfur source. As a part of organic matter, sulfur is bound in the structure, only to be released by soil microbes as temperatures warm up. Once it is released though, sulfur will be prone to leaching during high rainfall events. Leaching will be greater in sandy soils, as their large pore space is conducive to water movement, and their low charge (nutrient holding) allows sulfur to move easily. This means you should typically see sulfur deficiencies in sandier, low organic matter soils first. It is possible for sulfur deficiencies to correct themselves as temperatures warm up and organic matter releases sulfur. However, experience may also dictate that sandier soils require an application every year.
The University of Delaware recommends to monitor forages for sulfur deficiencies and to use ammonium sulfate as your N source to correct a deficiency. This fertilizer can lower your soil pH, so be sure to monitor the upper two inches of the soil, particularly if you have legumes in the mix. You may also consider crop removal of sulfur with hay production. For orchardgrass, tissue concentrations of sulfur should be between 0.2 to 0.3%. If you expect a yield of 3 tons/acre per year, that would only be a loss of 12-18 lbs of sulfur per year. That can easily be replaced with ammonium sulfate.