Plant-available S Mineralization from Northern Great Plains Soils.

Sulfur is a plant nutrient in many northern Great Plains soils. Crops such as canola are sensitive to low levels of S in soils and often respond to S fertilization. However, the current soil test using a 500 ppm P extractant as Ca(H2PO4)2 with turbidometric determination is inconsistent in providing reliable prediction of S deficient soils. Two studies were conducted to evaluate the role of S mineralization from soil organic matter (SOM). One study evaluated mineralization of S from SOM from 6 different landscape positions in the same field with SOM values ranging from < 1% to > 4%. In this study, selected soils were also amended with either wheat straw (low S residue) or alfalfa (high S residue). A second study evaluated the mineralization of S from 29 randomly selected soil samples submitted to the NDSU Soil Testing Laboratory with SOM values ranging from 0.9% to 19.6%. These studies indicated that (a) S immobilization may be significant in these soils, and (B) initial (short term) mineralization may be high but long term mineralization in most soils including high SOM soils is low. Implications for high S requiring crops will be discussed.