Historically, sulfur (S) deficiency has not been an issue for crop production in Iowa. Previous research documented sufficient plant available S for crop production on most soil associations (Alesii, 1982). Recent studies in corn and soybean production were consistent with results of previous research conducted across Iowa (Sawyer and Barker, 2002). The exception was a longstanding suggestion to apply S as commercial fertilizer or livestock manure for alfalfa production on sandy soils. However, over the past decade, alfalfa grown on some silt loam and loam soils in northeast Iowa has exhibited a slowly worsening problem with areas in fields of stunted growth and poor coloration. Recent investigations determined the growth problems were largely due to S deficiency. The following provides reasons for the developing problem, how to identify S deficiency, a summary of the research in northeast Iowa, and S fertilizer recommendations for alfalfa.