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 same as the highest yielding variety in soil pH near 4.5. (2016, 2017, 2018; on and near Central Ag Research Center, Highwood Bench; 95% confidence). 20 winter wheat and over 24 spring wheat varieties were grown. Not all varieties were grown in each location each year.
Winter wheat variety Years in highest yielding category/site-years planted Spring wheat variety Years in highest yielding category/site-years planted

Judee

SYClearstone2CL

SYMonument

Warhorse

 

2/3

4/5

3/3

3/5

Alum

Choteau

Egan

Lanning

NS PresserCL+

Oneal

Reeder

SyIngmar

4/5

2/3

3/3

3/4

2/2

2/3

2/3

2/2

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

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 out-yielded 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.

 
The following table as based on recommendations by Monica Pokorny (NRCS Plant Materials Specialist, Bozeman), Stuart Jennings (KC Harvey Environmental, Bozeman), a farmer trial, and Clain Jones’ observations. Seed a mix of 2-5 species and include a legume. To help select species adapted to given site characteristics, look at the Plant Guides produced by the USDA NRCS Plant Materials Program or TechnicalNotes produced by the USDA NRCS Bridger Plant Materials Center
 
Table 2. Acid tolerance of forage species
Common name Scientific name Cultivar(s) Acid tolerance1 Suitable sites

Native (N)

Introduced (I)

Perennial grasses observed to be good to excellent on at least one acidic agricultural soil in MT. *variety observed.

brome, meadow

Bromus biebersteinii

Cache*, Fleet*, Regar, Paddock

Marginal – Excellent

 

I

orchardgrass

Dactylis glomerata

Paiute*, Pennlate*

Fair - Excellent

 

I

wheatgrass, intermediate

Thinopyrum intermedium

Oahe*, Reliant, Manifest, Rush* Marginal - Excellent   I
wheatgrass, slender Elymus trachycaulus Copperhead, Pryor*, Revenue Marginal - Good Dry N

wheatgrass, western

Pascopyrum smithii

Rosana*, Rodan

Marginal - Good

 

N

wheatgrass, hybrid

Elytr. repens x Pseudo. spicata

NewHy*

     
Perennial grasses’ acid tolerance based in part on performance in mine-land reclamation site soils. Some of these may not be competitive in species mixes with aggressive introduced species.
bentgrass, creeping Atrostis stolonifera   Good Moist I
bentgrass, redtop Agrostis gigantea   Good Moist I
bluegrass, big Poa secunda spp. ampla Sherman Marginal - Excellent   N
bluegrass, Canby  Poa secunda spp.  canbyi  Canbar  Poor - Good   N
 bluegrass, Kentucky  Poa pratensis    Marginal - Excellent    I
bluegrass, Nevada  Poa secunda spp. nevadensis  Opportunity  Good Dry N
bluestem, little  Schizachyrium scoparium  Badlands, Blaze Average-Excellent   N
brome, fringed Bromus ciliatus   Good Dry N
brome, smooth Bromus inermis   Average-Good Dry I
fescue, hard Festuca brevipila Durar Average-Good   I
fescue, sheep Festuca oviina Covar Average-Good Dry I
foxtail, creeping Alopecurus arundinaceus Garrision, Retain Average Moist I
foxtail, meadow Alopecurus pratensis   Average Moist I
hairgrass, tufted Deschampsia cespitosa   Excellent Moist N
switchgrass Panicum virgatum Dacotah, Forestburg Good-Excellent Dry N
timothy Phleum pratense   Average-Good   I
wheatgrass, beardless/bluebunch Pseudoroegneria spicata Whitmar, Goldar, Anatone, P7 Poor-Fair Dry N
wheatgrass, streambank Elymus lanceolatus spp. riparium Sodar Poor-Good   N
wheatgrass, tall Thinopyrum ponticum Alkar, Jose Poor-Fair   I
wheatgrass, thickspike Elymus lanceolatus spp. lanceolatus Critana, Bannock Poor-Good   N
wildrye, Altai Elymus angustus   Poor-Good   I
wildrye, basin Elymus cinereus Trailhead, Washoe Poor-Good Dry N
wildrye, Canada Elymus canadensis Mandan Average-Good   N
Biennial  or short-lived perennial
ryegrass Lolium multiflorum as nurse or cover crop     I
Forbs / Legumes2          
alfalfa Medicago sativa   Marginal-Fair   I
birdsfoot trefoil Lotus corniculatus Leo, Empire Average-Good   I
clover, red Trifolium pratense   Marginal-Good   I
clover, white Trifolium repens   Marginal-Good   I
flax, Lewis Linum lewisii Appar, Maple Grove Marginal-Fair   N
sweetclover, yellow or white Melilotus officinalis, M. alba   Marginal-Good   I

1Range of acid tolerance from NRCS, MSU, farmer trial, and seed vendor resources.

2N fixation is greatly reduced in soils with pH below 5.5. Plants may need fertilizer N in low N soils.

 

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/