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Soil sampling requirements in Montana

Soil sampling requirements in Montana

State guidance: Montana State University Extension soil sampling advice.

Soil sampling in Montana: frequency, area, depth and cores

When in the year should soil be sampled in Montana?

How deep should soil samples be taken in Montana?

How many cores go into one soil sample in Montana?

Soil sampling rules in Montana, with the exact wording of each source
Country / region Purpose / programme Time / frequency Area per sample Method Depth Cores Status and source
United States
MontanaUnited StatesMontana only. Other states set their own rules.Routine soil fertility samplingMontana State University Extension soil sampling advice
  • Season Late fall to mid-spring for nitrogen. If sampled in fall above about 60 lb N/acre on soils under two feet deep, sample again in spring.
Not specifiedGrid for immobile nutrients, manure or high fertilizer history, or merged fields; zones for nitrogen, organic matter and pH, unknown history or yield linked to landscape. Uniform fields sampled at random. Georeference sampling points and return to them.Annual crops: 6 inches for most tests, at least 2 feet for nitrogen. Pasture and forage: 12 inches.Ten subsamples per composite is a reasonable average; 12 per field or zone for plus or minus 25 percent accuracy at 90 percent confidence.Official guidanceMSU Extension, The Soil Scoop: Soil Testing, Getting a Good Sample (PDF)
Who it applies to, the exact wording and every source
Who it applies to
Advice for Montana fields from Montana State University Extension. Not law.
Laboratory and analysis
Olsen phosphorus test, the basis of Montana P guidelines. Ask whether the lab is enrolled in a proficiency testing program; stay with a reliable lab in later years.
Field identifiers
Georeference sampling points with GPS; keep records of sampling locations and timing.
In force from
Under review
Legal text
MSU Extension, The Soil Scoop: Soil Testing, Getting a Good Sample (September 2025), and MontGuide MT200803AG, Soil Sampling Strategies (revised September 2017)

The wording in the source

Timing

  • Therefore, sampling in late fall to mid-spring is recommended to best capture growing season N availability.

    Soil Scoop, Timing

  • If fall nitrate levels are very high (e.g., greater than about 60 lb N/acre) and soil depth is less than two feet, a second sampling in spring is strongly suggested because there is a high likelihood of overwinter nitrate losses.

    Soil Scoop, Timing

Method

  • Grid sampling is good for fields with a history of manure or high fertilizer levels (especially P and K), and small fields merged to form a larger field.

    Soil Scoop, Location

  • Zone based sampling is suggested for fields with unknown or long cropping history, historically low levels of fertilization, no manure applications, and high with-in field variability or a relationship of yield to landscape.

    Soil Scoop, Location

  • Uniform fields can be randomly sampled throughout the entire field.

    MontGuide MT200803AG, Random Sampling

  • All sampling points should be georeferenced with a global positioning system (GPS) receiver and sampled in the same locations in subsequent years to track soil nutrient variation in a field, to see long-term trends, and to guide fertilizer application location.

    MontGuide MT200803AG, Types of Sampling

Depth

  • Pasture and forage get sampled to 12-inch depth, and annual crops to 6-inch for most characteristics and at least to 2-foot depth for N.

    Soil Scoop, Depth

Cores

  • Ten subsamples per composite sample is a reasonable average. More subsamples require more time, but improve accuracy.

    Soil Scoop, Number

  • if an accuracy level of ± 25% is deemed sufficient at a 90% confidence, then 12 subsamples per field (or zone) should be collected, composited and analyzed for nitrogen, phosphorus, and potassium.

    MontGuide MT200803AG, Number of Subsamples

Laboratory and analysis

  • For example, soil P levels in Montana soils are best tested with the Olsen rather than Bray or Mehlich tests, which are not suitable for soil pH greater than 6.

    Soil Scoop, Lab Selection

  • Also, Montana’s P fertilization guidelines are based on Olsen P values.

    Soil Scoop, Lab Selection

  • Ask if the lab is enrolled in a ‘proficiency’ testing program.

    Soil Scoop, Lab Selection

  • If a lab is reliable, stay with the same lab in subsequent years, because soil test results and recommendations can vary greatly among labs.

    Soil Scoop, Lab Selection

Field identifiers

Sources

Sources re-checked every two months, last update October 2026. Reviewed by GeoPard editorial team.

United States: federal rules and every other state

Soil sampling regulations in every country

Report an outdated requirement: info@geopard.tech

Plan the points to the rule that applies

Set the area per sample, the cores and the depth your rule asks for. GeoPard places the points on a grid or by zone, routes the walk, prints the labels and takes the plan to the field on a phone.

Create a sampling plan See the Soil Sampling Planner

A planning reference built from official sources, not legal advice. Rules apply by jurisdiction, nutrient, land use and programme: check the current official text and your laboratory’s instructions before fieldwork.

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