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Soil sampling requirements in Arizona

Soil sampling requirements in Arizona

State guidance: University of Arizona Cooperative Extension, soil sampling guide.

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

How often do you need to soil sample in Arizona?

How many acres can one soil sample cover in Arizona?

How deep should soil samples be taken in Arizona?

How many cores go into one soil sample in Arizona?

How many soil samples does a 100-acre field need in Arizona?

University of Arizona Cooperative Extension, soil sampling guide: A uniform 100-acre field needs at least 5 composite samples of no more than 20 acres each, and at least 75 cores in all, 15 per sample.

Samples and cores for any field size

Soil sampling rules in Arizona, with the exact wording of each source
Country / region Purpose / programme Time / frequency Area per sample Method Depth Cores Status and source
United States
ArizonaUnited StatesArizona only. Other states set their own rules.Soil sampling for commercial crop productionUniversity of Arizona Cooperative Extension, soil sampling guide
  • Repeat Regularly, if not every season, before planting each crop
Whole field sampling: one composite sample per 15 to 20 acresWhole field: random cores in a zigzag across the field. Grid: composites per grid cell or points at grid intersections. Zone: separate composites where variation is already known.12 inches for vegetables such as lettuce, spinach, broccoli, celery or cantaloupes. 24 inches for cotton, alfalfa, corn or wheat. Tilled soils to tillage depth.15 to 20 cores or scoops per site, depending on field size and the laboratoryOfficial guidanceUniversity of Arizona Cooperative Extension AZ2147 (PDF)
Who it applies to, the exact wording and every source
Who it applies to
Advice for commercial agriculture in Arizona from the University of Arizona Cooperative Extension. Not law.
In force from
Under review
Legal text
University of Arizona Cooperative Extension AZ2147, A Guide to Effective Soil Sampling for Sustainable Crop Production (July 2025)

The wording in the source

Timing

  • Growers managing agricultural lands are encouraged to test their soils regularly, if not every season, before planting each crop.

    AZ2147, Introduction

Area per sample

Method

  • Samples are collected randomly in a zigzag pattern across the field without consideration of any management practices or topographic features.

    AZ2147, 1. Whole Field Sampling

  • Grid sampling (Figure 4) is a type of spatial sampling that involves dividing the whole field into uniform grids.

    AZ2147, 2. Grid Sampling

  • The first method is done by collecting composite samples in the individual grid, which provides information about the area. The second method of grid sampling is done by collecting soil samples at the points created by the overlapping lines.

    AZ2147, 2. Grid Sampling

  • Zone sampling (Figure 5) is used when points of variation across a field are already known.

    AZ2147, 3. Zone Sampling

Depth

  • For example, if the crop is a vegetable such as romaine or iceberg lettuce, spinach, broccoli, celery, or cantaloupes, a 12-inch sampling depth is adequate; however, for crops like cotton, alfalfa, corn or wheat, a 24-inch sampling depth is recommended.

    AZ2147, Composite Sampling

  • For example, tilled soils only need to be taken to the depth that tilling has occurred.

    AZ2147, Composite Sampling

Cores

  • In general, 15 to 20 soil samples (cores or scoops) (Figure 2) are collected per site (or plot), depending on the size of the field and the requirements of the laboratory doing the testing.

    AZ2147, Composite Sampling

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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