Lichen sulfur contents as bioindicators of crop sulfur: deficiency or luxury uptake

The most important, immediate source of sulfur (S) for agricultural crops is the soil, but the soil supply is augmented by anthropogenic and natural S additions. In either case, lichen S contents provide a means for evaluating the effective S supply. Thus, lichen S content may be a way of determining locations where S emissions are large and extensive and why soil levels may vary from sufficient to deficient. Lichen S and phosphorus (P) contents were determined in two contrasting areas of the North Central United States, one east and one west of the Mississippi River. Mean contents were in microgram g(-1) S 4100 and P 1550 in Area East and S 2100 and P, 1660 in Area West. Population density and S emissions are much greater in Area East. Sulfur deficiencies are not generally recognized there. Area West includes regions that range from severely S deficient to adequate in soil S, with regions that are borderline predominating. Lichen S in the Gulf Coast Plain area and northwest of the Great Lakes was in the range 1000-2000 microgram g(-1). Sulfur deficiencies are well documented in the region, suggesting that 2000 microgram g(-1) lichen S-represents a boundary between near adequate and S-deficient crops unless soil sources are adequate. An east-west lichen S transect from southern Indiana to southwest Missouri suggests that a response to S fertilizer can be expected if the soil is sandy or lichen S is less than 2000 microgram g(-1) and crops are well supplied with other nutrients. High-S contents observed along the transect may have resulted from long-distance S transport from cities along the Missouri and Mississippi Rivers and the west shore of Lake Michigan. Lichen S contents along transects from Ontario, Canada, to the Gulf of Mexico ranged from 6000 microgram g(-1) near the Great Lakes to 1000 microgram g(-1) near the Gulf of Mexico. By using 2000 microgram g(-1) as the desired S level, half of the area is, to a certain extent, potentially S deficient.