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Soil sampling requirements in Washington

Soil sampling requirements in Washington

State rules: WAC 16-611-020, Recordkeeping requirements (dairy nutrient management). State guidance: WSU Extension, Eastern Washington Nutrient Management Guide (dryland winter wheat).

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

How often do you need to soil sample in Washington?

How deep should soil samples be taken in Washington?

Soil sampling rules in Washington, with the exact wording of each source
Country / region Purpose / programme Time / frequency Area per sample Method Depth Cores Status and source
United States
WashingtonUnited StatesWashington only. Other states set their own rules.Dairy soil analysis records: yearly postharvest nitrate and a soil analysis every three yearsDairy Nutrient Management Act, recordkeeping
  • Repeat Postharvest soil nitrate nitrogen analysis every year
  • Repeat A current soil analysis every three years (contents under Laboratory)
Not specifiedNot specifiedNot specifiedNot specifiedConditionalWAC 16-611-020, Washington State Legislature
Who it applies to, the exact wording and every source
Who it applies to
Dairy producers, who must keep records showing that nutrients applied to crop land were within acceptable agronomic rates.
Laboratory and analysis
Three-year analysis: organic matter, pH, ammonium nitrogen, phosphorus (Bray-1 below pH 7, Olsen bicarbonate at pH 7 or above), potassium and electrical conductivity.
In force from
29 November 2012
Legal text
WAC 16-611-020, Recordkeeping requirements (dairy nutrient management), WAC 16-611-020(2)(a)

The wording in the source

Timing

Who it applies to

  • (1) In accordance with RCW 90.64.010 (17)(c) and 90.64.102, dairy producers must maintain records to demonstrate that applications of nutrients to crop land are within acceptable agronomic rates.

    WAC 16-611-020(1)

Laboratory and analysis

  • (A) Organic matter; (B) pH; (C) Ammonium nitrogen; (D) Phosphorus (the Bray-1 method must be used to determine soil phosphorus for soils below pH 7 and the Olsen bicarbonate method must be used for soils at or above pH 7);

    WAC 16-611-020(2)(a)(ii)(A) to (D)

  • (E) Potassium; and (F) A measure of electrical conductivity.

    WAC 16-611-020(2)(a)(ii)(E) and (F)

In force

  • WSR 12-22-019, § 16-611-020, filed 10/29/12, effective 11/29/12.

    History note

Sources

Sources re-checked every two months, last update October 2026. Reviewed by GeoPard editorial team.
WashingtonUnited StatesWashington only. Other states set their own rules.Soil sampling for dryland winter wheat nutrient managementWSU Extension, Eastern Washington Nutrient Management Guide (dryland winter wheat)Not specifiedNot specifiedA field composite, or 2 to 3 management units by slope, aspect and drainage, each sampled separately.Winter wheat nitrogen: one-foot increments to at least 4 feet (121.92 cm) or a restrictive layer. Phosphorus: the surface foot, 0 to 12 inches (0 to 30.48 cm).Not specifiedOfficial guidanceWSU Extension EB1987E (PDF)
Who it applies to, the exact wording and every source
Who it applies to
Advice from the public land-grant university extension service for eastern Washington dryland winter wheat. Not law.
In force from
Under review
Legal text
WSU Extension EB1987E, Eastern Washington Nutrient Management Guide (published March 2005, revised July 2013)

The wording in the source

Method

  • If a field will be fertilized as one unit, collect cores from several representative locations throughout the field and combine these together for the sample.

    EB1987E, Box C

  • A typical field in eastern Washington may be divided into 2 to 3 management units based on slope, aspect, and drainage.

    EB1987E, Box C

Depth

  • For winter wheat, samples should be collected in one-foot increments to a minimum depth of four feet or a restrictive layer.

    EB1987E, B1

  • Phosphorus recommendations are based on soil test values in a surface one-foot sample (Table 1).

    EB1987E, Phosphorus (P) recommendations

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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