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Soil sampling requirements in California

Soil sampling requirements in California

State rules: Central Valley Regional Water Quality Control Board Order R5-2013-0122, Reissued Waste Discharge Requirements General Order for Existing Milk Cow Dairies. State guidance: University of California Cooperative Extension, guidelines for soil sampling.

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

How often do you need to soil sample in California?

When in the year should soil be sampled in California?

How deep should soil samples be taken in California?

How many cores go into one soil sample in California?

Soil sampling rules in California, with the exact wording of each source
Country / region Purpose / programme Time / frequency Area per sample Method Depth Cores Status and source
United States
CaliforniaUnited StatesCalifornia, Central Valley Region only: existing milk cow dairies under Order R5-2013-0122. Other regions and states set their own rules.Soil phosphorus monitoring on dairy land application areasCentral Valley Water Board, Dairy General Order (waste discharge requirements for existing milk cow dairies)
  • Repeat Once every 5 years from each land application area. May be spread over 5 years by sampling 20 percent of the areas each year.
Not specifiedNot specifiedNot specifiedNot specifiedConditionalCentral Valley Water Board Order R5-2013-0122 with Monitoring and Reporting Program (PDF)
Who it applies to, the exact wording and every source
Who it applies to
Existing milk cow dairies in the Central Valley Region covered by the General Order, on each land application area.
Laboratory and analysis
Laboratory analysis for soluble phosphorus. Spring and fall pre-plant nitrate, organic matter and other tests at 0 to 1 foot and 1 to 2 feet are recommended but not required.
In force from
Under review
Legal text
Central Valley Regional Water Quality Control Board Order R5-2013-0122, Reissued Waste Discharge Requirements General Order for Existing Milk Cow Dairies, Monitoring and Reporting Program, Table 2 (Nutrient Monitoring, Soil)

The wording in the source

Timing

Who it applies to

  • REISSUED WASTE DISCHARGE REQUIREMENTS GENERAL ORDER FOR EXISTING MILK COW DAIRIES

    Order title page

  • all Dischargers specified by the Central Valley Water Board and all Dischargers that were formerly regulated under the original version of Order R5-2007-0035 adopted in May 2007, their agents, successors, and assigns shall comply with the following:

    Order, operative paragraph after Finding 44

Laboratory and analysis

Sources

Sources re-checked every two months, last update October 2026. Reviewed by GeoPard editorial team.
CaliforniaUnited StatesCalifornia only. Other states set their own rules.General fertility and nitrate samplingUniversity of California Cooperative Extension, guidelines for soil sampling
  • Repeat General fertility: every 3 years is common
  • Season Spring or fall, at the same time each year, not after fertilizer
  • Repeat Nitrate-N: every year, preplant or before fertilization
Not specifiedW-shaped pattern, a zigzag across the whole block, or a diagonal line. Divide non-uniform fields into blocks by cropping history and varieties, observed differences in crop development, and soil series.General fertility: 6 inches or tilling depth. Nitrate-N: 6 inches to 3 feet, by rooting depth and leaching risk.At least 20 cores per blockOfficial guidanceUCCE, Guidelines for Soil Sampling (PDF, UC ANR)
Who it applies to, the exact wording and every source
Who it applies to
Advice for California growers from University of California Cooperative Extension (UC Agriculture and Natural Resources). Not law.
In force from
Under review
Legal text
UC Cooperative Extension (Small Farms Advisor, Yolo, Solano and Sacramento Counties), Guidelines for Soil Sampling

The wording in the source

Timing

Method

Depth

Cores

  • Take a minimum of 20 cores for the block, which are mixed in 1 clean bucket, from which a single subsample is removed for lab testing

    Protocol, Taking a soil sample

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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