Farm406

armers in several Montana counties are experiencing nearly complete yield loss in portions of their fields due to soil acidity (low pH). Traditionally, soil acidity was not an issue in Montana as most soils in agricultural areas were naturally high pH. However, over the past thirty years, there has been an almost three-fold increase in nitrogen fertilizer use which has accelerated soil acidification. Montana State University soil scientists, Extension Agents, crop advisers, and producers have now identified fields in 21 Montana counties with soil pH levels below 5.5, some as low as 3.8. Three years ago, Montana State University faculty members from the Central Agricultural Research Center were asked why portions of a wheat field in Chouteau County were failing. All the usual potential causes were ruled out and soil acidification, which causes aluminum toxicity, was found to be the problem. Currently, a cooperative research effort led by Rick Engel, Clain Jones and Scott Powell (LRES faculty), faculty and staff at the Central Ag Research Center (led by Pat Carr), the Montana Salinity Control Association (Jane Holzer), Chouteau County Extension (Tyler Lane), Chouteau County Conservation District (Dale Krause), and several farmers has been organized to develop prevention, mitigation, and adaptation options to manage this problem. Montana's Fertilizer Check-off Fund and the USDA Western Sustainable Agriculture Research and Education Program are supporting this study. Based on regional research, the major cause of soil acidification in Montana is the use of ammonium-based fertilizers, including urea. Although an excellent fertilizer nitrogen source, when the nitrogen in urea gets converted to nitrate, hydrogen ions are released, lowering soil pH. No-till concentrates the acidity near the surface where fertilizer is applied. This produces extreme differences in soil pH with depth on many Montana fields. Often the surface pH (0 to 3-inch depth) will be 2 to 3 units lower than pH at the 12 to 15-inch depth. Because Montana soils are pH stratified, collecting samples in a standard 0 to 6-inch depth increment may mask potential problems at the surface. Also, pH across Montana farm fields can vary greatly. The lowest surface soil pH is often found in low lying or toe-slope areas and may be 2 pH units higher on or near a ridge less than 100 yards away. Therefore, mixing soil samples or cores across multiple landscape positions may not be helpful in identifying fields with soil acidity problems. At pH levels below 5.0, naturally-occurring soil metals like aluminum and manganese become more soluble and can stunt root and shoot growth. Young plants in acidic 31 farm406 Montana counties in 2018 with at least one field reporting soil pH < 5.5. Markers do not indicate exact location of the field. F

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