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Updated: April 10, 2018
Plant and soil surveys in 2014, 2015 and 2016 were conducted across PA. Extension educators in 23 counties collected 124 plant and soil samples from production fields. Corn earleaf samples were collected at silking along with a soil sample collected in close proximity. Samples were analyzed in AASL. In addition, 16 sulfur response experiments with potassium sulfate, ammonium sulfate and gypsum (calcium sulfate) were conducted on farms across PA in 2015-16.
Results of the survey are summarized in the table below. The normal range of Mehlich 3 soil test S for agronomic soils in Pennsylvania is 10 to 25 ppm. Most of the survey results were in the "Normal" range for S in PA soils. A Mehlich 3 S level of 10 ppm has been suggested as the level below which S response is expected. While most of the survey samples were above this level, soil testing for S is not an especially reliable method of predicting S need. Plant tissue S is a much more reliable indicator of S status of a crop. The AASL sufficiency range for corn earleaf S is 0.2 to 0.5%. In the survey, 75% of sites had earleaf S concentration below the sufficiency range. With a less conservative lower limit of 0.15% S, used by many labs, only about 10% would be below that level.
Manure is a good source of S, so the survey data was analyzed to evaluate differences in soil and plant S due to the frequency of manure application. Survey results did show a slight trend toward higher soil test S with more frequent manure application; however, there was very little difference in plant S due to the frequency of manure application. Overall, the survey indicates that most of the fields were in the normal range for soil test S and marginal or low in the plants.
Mehlich 3 S, ppm
Earleaf S, %