Soil sampling requirements in Iowa

Q: How many soil samples does a 100-acre field need in Iowa?

Under Iowa DNR manure management plans (MMP) for confinement feeding operations: A uniform 100-acre field needs at least 10 composite samples of no more than 10 acres each, and at least 100 cores in all, 10 per sample.

State rules: Iowa Administrative Code 567, Chapter 65 (Animal Feeding Operations). State guidance: Iowa State University Extension and Outreach soil sampling advice.

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

How often do you need to soil sample in Iowa?

Iowa DNR manure management plans (MMP) for confinement feeding operations Conditional Result valid: Soil samples must be four years old or less. A complete plan with new soil sampling for each field at least once every four years.
Iowa State University Extension and Outreach soil sampling advice Official guidance Every 2 to 4 years for most crops, or once in a crop rotation, in the same crop each time.

When in the year should soil be sampled in Iowa?

Iowa State University Extension and Outreach soil sampling advice Official guidance Ideally after harvest and before fertilization. Not shortly after lime, fertilizer or manure. Avoid winter and frozen soil.

How many acres can one soil sample cover in Iowa?

Iowa DNR manure management plans (MMP) for confinement feeding operations Conditional No more than 10 acres per sample. One sample for a field of 15 acres or less. Up to 20 acres for the next sampling where manure went on at phosphorus-based rates.
Iowa State University Extension and Outreach soil sampling advice Official guidance Grid: a suggested minimum of one sample per 2.5 acres. Beyond that, zone sampling is likely more effective. Otherwise one sample per uniform area.

How deep should soil samples be taken in Iowa?

Iowa DNR manure management plans (MMP) for confinement feeding operations Conditional 0 to 6 inches.
Iowa State University Extension and Outreach soil sampling advice Official guidance P, K, Zn and organic matter: 0 to 6 inches in all tillage systems. pH: 0 to 6 inches with tillage, top 2 to 3 inches in no-till and in hay or pasture.

How many cores go into one soil sample in Iowa?

Iowa DNR manure management plans (MMP) for confinement feeding operations Conditional At least 10 cores per composite sample.
Iowa State University Extension and Outreach soil sampling advice Official guidance At least 10 to 12 cores per sample. 15 to 20 for a better average. At least 20 with recent banded fertilizer or manure.

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

Iowa DNR manure management plans (MMP) for confinement feeding operations: A uniform 100-acre field needs at least 10 composite samples of no more than 10 acres each, and at least 100 cores in all, 10 per sample.

Samples and cores for any field size

Soil sampling rules in Iowa, with the exact wording of each source
Country / region	Purpose / programme	Time / frequency	Area per sample	Method	Depth	Cores	Status and source
United States
IowaUnited StatesIowa only. Other states set their own rules.	Soil phosphorus and pH tests for the phosphorus indexIowa DNR manure management plans (MMP) for confinement feeding operations	Result valid Soil samples must be four years old or less Repeat A complete plan with new soil sampling for each field at least once every four years	No more than 10 acres per sample. One sample for a field of 15 acres or less. Up to 20 acres for the next sampling where manure went on at phosphorus-based rates.	Grid, management zone or soil type sampling, among others. Procedural details may be taken from ISU Extension CROP 31-8 (published as CROP 3108), NCR-13 Report 348 or other credible soil sampling publications.	0 to 6 inches	At least 10 cores per composite sample	ConditionalIowa Administrative Code 567, Chapter 65 (PDF, IAC 8/6/25)
Who it applies to, the exact wording and every source Who it applies to Anyone who must submit a manure management plan for a confinement feeding operation: construction permit applicants, owners of operations built or expanded after May 31, 1985 or building a manure storage structure, and people applying manure in Iowa from out-of-state confinement operations. Covers each field in the plan, the fields where the phosphorus index must be used. Outside the rule Small animal feeding operations (SAFO, 500 or fewer animal units), operations of 500 or fewer animal units that elect SAFO status for updated plans, construction permit applicants for an egg washwater storage structure, and research colleges for their research activities. Laboratory and analysis Phosphorus and pH. A laboratory enrolled in the IDALS soil testing certification program. Bray-1 phosphorus not accepted where soil pH is 7.4 or higher. In force from Under review Legal text Iowa Administrative Code 567, Chapter 65 (Animal Feeding Operations), Rule 567-65.111(11) and 65.111(12) The wording in the source Timing Soil samples shall be obtained from each field in the MMP, and the soil samples shall be four years old or less. 567 IAC 65.111(11) An operation must submit a complete MMP using a new phosphorus index, including soil sampling as required in subrule 65.111(11), for each field in the MMP a minimum of once every four years. 567 IAC 65.111(12)"h"(3) Area per sample Each soil sample shall represent no more than ten acres. For fields less than or equal to 15 acres, only one soil sample is necessary. 567 IAC 65.111(11)"c" If manure is applied as phosphorus-based rates within soil sampling periods, each soil sample may represent up to 20 acres for the next required soil sampling. 567 IAC 65.111(11)"f" Method Acceptable soil sampling strategies include but are not limited to grid sampling, management zone sampling, and soil type sampling. 567 IAC 65.111(11)"a" Procedural details can be taken from Iowa State University Extension and Outreach publication CROP 31-8, “Take a Good Soil Sample to Help Make Good Fertilization Decisions,” NCR-13 Report 348, “Soil Sampling for Variable-Rate Fertilizer and Lime Application,” effective January 1, 2001, or other credible soil sampling publications. 567 IAC 65.111(11)"a" Depth with each core containing soil from the top six inches of the soil profile. 567 IAC 65.111(11)"b" Cores Each soil sample must be a composite of at least ten soil cores from the sampling area, with each core containing soil from the top six inches of the soil profile. 567 IAC 65.111(11)"b" Who it applies to Soil sampling requirements for fields where the phosphorus index must be used. Soil samples shall be obtained from each field in the MMP 567 IAC 65.111(11), heading An applicant for a construction permit for a confinement feeding operation. 567 IAC 65.110(1)"a" The owner of a confinement feeding operation, other than a SAFO, if one of the following applies: 567 IAC 65.110(1)"b" The owner constructs a manure storage structure, regardless of whether the person is required to be issued a permit for the construction 567 IAC 65.110(1)"b"(2) A person who applies manure in Iowa that was produced in a confinement feeding operation, other than a small operation, located outside of Iowa. 567 IAC 65.110(1)"c" The confinement feeding operation was constructed or expanded after May 31, 1985, regardless of whether the confinement feeding operation structure was required to have a construction permit. 567 IAC 65.110(1)"b"(1) A person who submits an MMP shall include a phosphorus index as part of the MMP as required in subrule 65.111(12). 567 IAC 65.111(1)"c" Outside the rule “Small AFO” or “SAFO” means an AFO that has an animal unit capacity of 500 or fewer animal units. 567 IAC 65.1, definitions However, an MMP shall not be required of an applicant for an egg washwater storage structure or for a SAFO. 567 IAC 65.110(1)"a" An AFO otherwise required to submit an updated MMP and pay an annual compliance fee may make an election to be considered a SAFO for purposes of filing updated MMPs and annual compliance fees if the confinement feeding operation maintains an animal unit capacity of 500 or fewer animal units. 567 IAC 65.110(1)"e"(2) A research college is exempt from this subrule and the MMP requirements of rule … for research activities and experiments performed under the authority of the research college and related to confinement feeding operations. 567 IAC 65.110(1)"e"(1) Laboratory and analysis Each soil sample shall be analyzed for phosphorus and pH. 567 IAC 65.111(11) Soil analysis must be performed by a lab enrolled in the Iowa department of agriculture and land stewardship (IDALS) soil testing certification program. 567 IAC 65.111(11)"d" If soil pH is greater than or equal to 7.4, soil phosphorus data from the Bray-1 extraction method is not acceptable for use with the phosphorus index. 567 IAC 65.111(11)"e" Sources Iowa Administrative Code 567, Chapter 65 (PDF, IAC 8/6/25) Law Sources re-checked every two months, last update October 2026. Reviewed by GeoPard editorial team.
IowaUnited StatesIowa only. Other states set their own rules.	Routine soil fertility samplingIowa State University Extension and Outreach soil sampling advice	Repeat Every 2 to 4 years for most crops, or once in a crop rotation, in the same crop each time Season Ideally after harvest and before fertilization. Not shortly after lime, fertilizer or manure. Avoid winter and frozen soil.	Grid: a suggested minimum of one sample per 2.5 acres. Beyond that, zone sampling is likely more effective. Otherwise one sample per uniform area.	Soil map unit or management zone sampling, or grid sampling. Cores in a random zigzag pattern across each area; grid points cover an area at least 50 feet across.	P, K, Zn and organic matter: 0 to 6 inches in all tillage systems. pH: 0 to 6 inches with tillage, top 2 to 3 inches in no-till and in hay or pasture.	At least 10 to 12 cores per sample. 15 to 20 for a better average. At least 20 with recent banded fertilizer or manure.	Official guidanceISU Extension and Outreach CROP 3108 (PDF, copy hosted by Iowa DNR)
Who it applies to, the exact wording and every source Who it applies to Advice for Iowa fields from Iowa State University Extension and Outreach. Not law. Iowa manure management rules point to it for procedure. Laboratory and analysis Tell the laboratory when the pH sample came from 2 to 3 inches or the lime will not be incorporated. Field identifiers Each bag identifies the field and sample area with a unique number. In force from Under review Legal text ISU Extension and Outreach CROP 3108, Take a Good Soil Sample to Help Make Good Fertilization Decisions (December 2016) The wording in the source Timing Fields should be sampled every 2-4 years for most crops, or once in a crop rotation. CROP 3108, How often to sample and test, p. 4 Fields should be in the same crop each time sampled in order to reduce the temporal variability of test results. CROP 3108, How often to sample and test, p. 4 Ideally, the best time would be after harvest and before fertilization. Do not sample shortly after a lime, fertilizer, or manure application or when the soil is excessively dry or wet. CROP 3108, When to sample, p. 1 Sampling at other times such as in the winter, and especially with frozen soil, is discouraged CROP 3108, When to sample, p. 1 Area per sample No one grid size best fits all fields, but a suggested minimum size is one sample per 2.5 acres. If considering a larger grid sampling size, a zone sampling approach would likely be more effective. CROP 3108, Sampling using a grid pattern, p. 3 Each sample should represent a uniform field area with similar past management. CROP 3108, Sampling using soil maps and management zones, p. 1 Method For soil map unit and management zone sampling, or to represent the entire area of a grid cell, take separate cores in a random zigzag pattern from each sampling area. CROP 3108, Collecting a representative sample, p. 4 For grid-point sampling, take the cores in a random pattern from the area of the identified sample point, which should be at least 50 feet in diameter. CROP 3108, Collecting a representative sample, p. 4 Depth Use this sample depth in all tillage systems when sampling for P, K, Zn, and organic matter. CROP 3108, Sampling depth, p. 4 (the depth is 0 to 6 inches) from a depth of 0 to 6 inches because research has shown that is the best and most cost-effective depth for Iowa conditions. CROP 3108, Sampling depth, p. 4 Samples for pH and buffer pH should be collected from a depth of 6 inches when the field is managed with tillage, but from the top 2-3 inches in no-till fields and forages for hay or pasture CROP 3108, Sampling depth, p. 4 Cores As a minimum, take 10-12 cores or borings per sample and place all soil in a sample bag. CROP 3108, Collecting a representative sample, p. 4 For better representation of the average condition within an area, take 15 to 20 cores. Take at least 20 cores if the field has recent banded fertilizer or manure. CROP 3108, Collecting a representative sample, p. 4 Laboratory and analysis In these tillage and cropping conditions the laboratory must be informed that the sample was taken from a depth of 2-3 inches or that the lime will not be incorporated. CROP 3108, Sampling depth, p. 4 Field identifiers Check that each bag clearly identifies the field and sample area with a unique number. CROP 3108, Sending samples for testing, p. 4 Sources ISU Extension and Outreach CROP 3108 (PDF, copy hosted by Iowa DNR) Guidance 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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Soil sampling requirements in Iowa

Soil sampling requirements in Iowa

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

How often do you need to soil sample in Iowa?

When in the year should soil be sampled in Iowa?

How many acres can one soil sample cover in Iowa?

How deep should soil samples be taken in Iowa?

How many cores go into one soil sample in Iowa?

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

The wording in the source

Timing

Area per sample

Method

Depth

Cores

Who it applies to

Outside the rule

Laboratory and analysis

Sources

The wording in the source

Timing

Area per sample

Method

Depth

Cores

Laboratory and analysis

Field identifiers

Sources

Plan the points to the rule that applies

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