Acidity assessment

  • 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.
  • Test a top 3-inch soil/water slurry with a pH meter stick (MSU does not advocate any one product; this is provided as an example of a field pH 'stick') 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).
  • This AgAlert briefly explains what to look for. Dr. Amber Moore's WERA-103 presentation explains the ins and outs of soil pH and buffer pH testing.

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). Watch The Ins and Outs of Soil pH and Buffer pH Testing for more information.
  • 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)

Table 1. Small grain varieties yielding (bu/acre) same as the highest yielding variety in soil pH near 4.5 (2016, 2017, 2018) Central Ag Research Center Highwood Bench field trials; 95% confidence).
Winter wheat Spring wheat
2016 2017 2016 2017 2018 (Citadel site)

SyClearstone2CL (68.5)

Warhorse (68.3)

Judee (66.0)

SyClearstone2CL (67.6)

SYMonument (65.0)*

Decade (64.2)

Loma (60.9)

Northern (60.5)

SYWolf (60.4)

Alum (46.4)

Egan (42.2)

Lanning (40.3)*

Oneal (38.9)

SyIngmar (37.8)*

Alum (37.7)

Egan (37.5)

Choteau (37.7)

Reeder (37.0)

NSPresserCL+ (34.7)*

SySoren (34.2)

Lanning (48.1)

MT 1621 (47.6)*

Alum (43.5)

http://agresearch.montana.edu/carc/reports-pdf/2017%20Annual%20Report.pdf

* indicates variety not grown in prior year(s)

Spring Wheat: At 2 additional low soil pH fields in Highwood bench area, 2018 trials found no varieties out-producing the others.

Barley: There was high variation between malting barley yields in 2016 and 2017. None were significantly higher yielding than others in either year. 10WA.107.43 was first grown in 2018 and outyielded the other varieties by 5 bu/ac on one low pH soil field but not another.

Canola: Canola yields are sensitive to soil pH. There were no outstanding varieties on both Highwood bench sites with low pH soil in 2018. On low pH soil, top producing varieties (HyCLASS and DKL 70-10) yielded no greater than the average.

 
Table 2. Plants suitable for acid sites*. Seed a mix of 2-5 species and include a legume.
Perennial, dry site Perennial, moist site Annual Legume
'Copperhead' slender wheatgrass; Elymus trachycaulus ssp. trachycaulus creeping foxtail; Alopecurus arundinaceus annual ryegrass; Lolium multiflorum as nurse or cover crop birdsfoot trefoil; Lotus corniculatus
'Opportunity' Nevada bluegrass; Poa nevadensis meadow foxtail; Alopecurus pratensis   red clover; Trifolium pratense
'Goldar' bluebunch wheatgrass; Pseudoroegneria spicata  tufted hairgrass; Deschampsia cespitosa    
 Indian ricegrass; Achnatherum hymenoides  creeping bentgrass; Agrostis stolonifera    
fringed brome; Bromus ciliatus      
smooth brome; Bromus inermis (very aggressive)      
 sheep fescue; Festuca ovina      
 switchgrass; Panicum virgatum      
 'Washoe' basin wildrye; Leymus cinereus      
 redtop bentgrass; Agrostis gigantea      
 rough bentgrass; Agrostis scabra      

*Provided by Monica Pokorny, NRCS Plant Materials Specialist, Bozeman, and Stuart Jennings, KC Harvey Environmental.

Bridger Plant Materials Center, has publications on most of the above species https://www.nrcs.usda.gov/wps/portal/nrcs/main/plantmaterials/pmc/west/mtpmc/, and a technical note with species suggestions and descriptions https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/mtpmctn12232.pdf

 

We will post our study results on this webpage and upcoming events on the soil acidification homepage and the MSU Soil Fertility website. Watch for field days, workshops, press releases, radio interviews, and a video.

References cited:

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/