Soil Acidification: Measure & Manage
- Look for unexplained poor health generally in low or mid-slope areas. Symptoms of aluminum and manganese toxicity are shown on the Nutrient Deficiency and Toxicity webpage.
- Use pH color strips to test a top 3-inch soil/water slurry where low pH is suspected. Field tests help select soils to send to laboratory. They do not provide enough information to determine lime requirements; laboratory buffer tests are necessary for lime rate calculations.
- Look at standard soil tests for composited soil from a field in the top 6 inches. If pH < 6 it is likely the field will have spots close to or below pH 5. If pH > 6, don't assume there are no areas with low pH.
- Soil test top 3 inches from affected regions for soil pH and/or KCl extractable aluminum (Al). If soil pH < 5 or Al > 5ppm then soil acidity is likely a concern.
- Compare manganese (Mn) tissue analysis from 'good' and 'bad' crop areas. Tissue Mn > 500 ppm is likely a problem (Ohki, 1984) . Aluminum does not translocate very well from roots to shoots, so shoot tissue analysis for Al is not worthwhile. Also, since acid tolerant crop varieties have lower leaf Al concentrations than acid sensitive ones, it is difficult to provide critical concentration levels for a crop (Foy, 1996).
Manage low pH
Tools and steps for remediation, adaptation and prevention are detailed in other materials listed on our Resources page.
Until we have regionally specific results:
- Ask a lab to use Woodruff, SMS, Sikora, Mehlich, or modified Mehlich buffer test to determine buffer pH and liming needs (Thompson et al., 2016).
- Use soil test lab recommended liming rates or use the equation from Washington State University:
Lime rate (ton/acre) = 1.86 x (final desired pH - 4.6)
- Consider aluminum or low-pH tolerant species (Table 1; http://agresearch.montana.edu/carc/reports-pdf/2017%20Annual%20Report.pdf).
We will post our study results and upcoming events on this webpage and the MSU Soil Fertility website. Watch for field days, workshops, press releases, radio interviews, and a video.
Foy, C.D. 1996. Tolerance of durum wheat lines to an acid, aluminum-toxic subsoil. J. Plant Nutr. 19:10-11. doi:10.1080/01904169609365206
Ohki, K. 1984. Manganese deficiency and toxicity effects on growth, development, and nutrient composition in wheat. Agron. J. 76:213–218
Thompson, W.H., C. McFarland, and T. Brown. 2016. Agricultural Lime and Liming Part 2. Laboratory Testing to Determine Lime Requirements. Washington State University Extension FS217E http://pubs.wpdev.cahnrs.wsu.edu/pubs/fs217e/