Temporal Trends of Sulfur Levels in Northwest Ohio Soils.

Sulfur (S) is an essential nutrient for plant growth. The use of more concentrated NPK fertilizers (with less S in their composition), improved crop yields leading to higher requirement/exportation of S, and reduced atmospheric inputs due to improved air quality have all been hypothesized as causing a depletion in plant-available soil S concentrations. However, despite increasing reports of yield responses of crops to S fertilization, there is little information about the changes in the soil test concentrations of S. The aim of this study was to use a soil-test database from northwest Ohio farms to look for changes in soil S test levels over time. The dataset was composed of 8,200 soil tests taken by an agriculture consultant company. The soil samples were collected between 2002-2014 from the 0-18 cm layer on 143 farm fields located in Allen, Defiance, Paulding and Williams counties, Ohio. The sulfate-S from samples was extracted by Mehlich III and determined by the turbidimetric method. The results of the soil tests were organized by farms and also grouped into one large database for analyses. The results showed a significant (p < 0.001) linear and decreasing trend of soil test S concentrations with passage of time for all farms. The large, combined database showed the following relationship: S (mg/kg) = 32.1 - 1.7*year with an R² = 0.86. These data also indicated soil test values were often below critical concentrations needed to support high crop yields. The principal component analysis (PCA) did not show other soil chemical properties related to the S decreases, indicating that current fertilization practices and wet deposition (acid rain) have not been able to maintain adequate plant-available S concentrations in soil. It is essential that greater attention be paid to maintain and/or increase soil test S concentrations to optimize crop productivity.