Why, When & How to Test Your Soil

 
Frequently Asked Questions
 

Soil Testing: Understanding and Managing the Foundation of Your Crop

Choosing high-quality varieties, receiving favorable weather, providing adequate water, and managing pests and diseases are all important parts of producing a successful crop. However, one crucial factor should never be overlooked: the soil in which that crop is growing. Soil testing gives growers a practical way to better understand what is happening beneath their crops and make more informed fertility and soil-management decisions.

The Big Picture

Successful crop production is rarely determined by one factor. Variety selection, soil conditions, weather, fertility, irrigation, pest and disease pressure, pollination, and management practices can all influence crop performance. Soil is one of the major factors growers can evaluate and manage, and it should not be overlooked.

Why Should I Test My Soil?

 

A soil fertility test can provide valuable information about the chemical condition of your soil and help determine whether nutrient or pH adjustments may be beneficial.

Depending on the laboratory and testing package selected, a soil test may evaluate:

Soil Chemistry
Soil pH
Phosphorus
Potassium
Calcium
Magnesium
Additional Measurements
Other macro- or micronutrients
Organic matter
Soluble salts or electrical conductivity
Recommendations
Lime requirements
Crop-specific fertilizer recommendations

Not every laboratory measures the same properties in a standard test. Growers should review what is included in the test they select and choose additional analyses when appropriate. Soil testing can help identify nutrients that may already be present in sufficient amounts, nutrients that may require attention, and soil pH conditions that could affect nutrient availability.

Why Is Soil pH Important?

 

Soil pH measures how acidic or alkaline the soil is. It is an important part of soil fertility because pH influences chemical and biological processes in the soil, including the availability of plant nutrients.

A nutrient can be present in the soil without necessarily being available to a plant in the amount it needs. Soil pH is one factor that influences that availability.

Different crops can also perform best within different pH ranges. There is no single ideal soil pH for every crop and every soil, which is why soil-test results should be interpreted according to the crop being grown rather than simply looking at the pH number by itself.

Can Soil Contain Nutrients That Plants Still Have Difficulty Using?

 

Yes. The amount of a nutrient physically present in soil and the amount that is available for plant uptake are not necessarily the same thing. Soil pH, soil chemistry, moisture, biological activity, root development, and other conditions can influence nutrient availability.

This is why simply applying more fertilizer is not always the correct response when plants show symptoms that appear to be related to nutrition. A soil test, combined with observations of the crop and growing conditions, can provide much better information than guessing based on plant appearance alone.

Does a Standard Soil Test Measure Nitrogen?

 

Not necessarily. Nitrogen behaves differently in soil than many other nutrients, and forms such as nitrate can change considerably with rainfall, temperature, biological activity, crop uptake, and other conditions.

Some laboratories offer specific nitrogen or nitrate testing, while routine fertility packages may focus primarily on pH, phosphorus, potassium, calcium, magnesium, and other measurements. Growers should check with their laboratory to determine exactly what is included in the test being ordered.

When Should Soil Be Tested?

 

Soil should ideally be tested early enough to allow time to receive the results, interpret the recommendations, and make any necessary adjustments before planting.

Fall

Often an excellent time to test because it provides time to plan fertility programs and make recommended pH adjustments before the following growing season.

Early Spring

Can also be useful when fall testing was not completed.

Established Production Areas

Testing every few years is commonly recommended, although the appropriate interval depends on the crop, management intensity, previous results, and changes being made to the soil.

Consistency is important. When comparing results over several years, sampling the same areas at approximately the same time of year and using consistent sampling methods can make those comparisons more meaningful.

Should I Test Before Starting a New Garden or Production Area?

 

Yes, whenever practical. Testing before planting provides an opportunity to identify fertility or pH concerns while they may still be easier to address.

Once perennial plants or permanent production systems are established, incorporating some amendments throughout the root zone can become considerably more difficult. A preplant soil test can also provide a useful baseline for future comparisons.

How Do I Collect a Soil Sample?

 

A laboratory can only analyze the soil that is submitted, so the quality of the sample is extremely important. One handful of soil from one corner of a field or garden may not accurately represent the entire area.

A composite sample is generally created by collecting multiple subsamples from throughout an area that is reasonably uniform. Those subsamples are thoroughly mixed together, and a portion of that mixture is submitted to the laboratory.

  1. Obtain the sampling instructions and appropriate container or bag from the laboratory you plan to use.
  2. Use clean sampling equipment such as a soil probe, auger, shovel, or trowel.
  3. Remove surface debris when appropriate without removing the soil itself.
  4. Collect multiple subsamples throughout the area being tested.
  5. Maintain a consistent sampling depth.
  6. Combine the subsamples in a clean container.
  7. Mix the soil thoroughly.
  8. Prepare and submit the sample according to the laboratory's instructions.

The laboratory's instructions should always take priority because sampling depth, sample preparation, and submission requirements can vary depending on the crop and type of analysis.

Soil from a production field
Soil conditions can vary within the same field, which is why representative sampling and consistent sampling methods are important.

How Deep Should I Sample?

 

There is no single sampling depth that is correct for every situation. Sampling depth can vary depending on whether the area is conventionally tilled, no-till, pasture, lawn, garden, orchard, or another production system. The type of analysis being performed can also affect sampling recommendations.

The best practice is to follow the sampling depth recommended by the laboratory or Extension service being used and then remain consistent when monitoring the same area over time.

Where Should I Take the Samples?

 

Samples should represent the area you actually want to understand. When collecting a composite sample, distribute the subsamples throughout the area rather than taking all of them from one location.

Avoid including unusual areas that do not represent the rest of the field or garden, such as:

  • Fertilizer bands
  • Field borders and lanes
  • Wet depressions
  • Severely eroded areas
  • Areas where manure, compost, lime, or fertilizer was recently concentrated
  • Unusual sandy or gravelly areas
  • Locations immediately beside roads or structures
  • Other visibly different areas

If those areas are important to investigate, they can be sampled separately.

What If One Part of My Field or Garden Performs Differently?

 

Consider sampling it separately. If one portion of a field consistently produces differently, has noticeably different soil, drains differently, has a different management history, or shows recurring crop problems, combining it with soil from the rest of the field can hide useful differences.

For example, if most of a field is performing normally but one section repeatedly performs poorly, a separate sample from the affected area can be compared with a representative sample from the normally performing area. That comparison may provide more useful information than mixing both areas into one sample.

Why Does the Laboratory Ask What Crop I Plan to Grow?

 

Fertilizer and lime recommendations are not based solely on the numbers measured in the soil. Different crops have different nutrient requirements and can respond differently to soil fertility and pH. Yield goals and production systems can also influence nutrient-management decisions.

Providing the correct crop information allows the laboratory or Extension service to interpret the soil test in a way that is more relevant to what you actually intend to grow.

Should I Apply Fertilizer Every Year Even If the Crop Looks Good?

 

Not automatically. Routine fertilizer applications without knowing existing soil fertility can result in unnecessary expense and nutrient accumulation.

The goal of fertility management is not simply to apply more nutrients. It is to provide appropriate nutrients in amounts and at times that correspond with crop needs while accounting for nutrients already available from the soil and other sources. A soil test can help growers make those decisions more efficiently.

Can Too Much Fertilizer Be a Problem?

 

Yes. More fertilizer does not automatically produce a better crop. Excessive nutrient applications can increase production costs, create nutrient imbalances, contribute to excessive salt levels in some situations, and increase the potential for nutrient losses into the surrounding environment.

The goal should be appropriate fertility, not maximum fertilizer. Good nutrient management considers the nutrient source, application rate, timing, and placement while accounting for soil-test results and crop requirements.

Should I Use a Home Soil Test Kit or a Laboratory?

 

Home testing kits can be useful for quick estimates or educational purposes, particularly for measurements such as pH.

However, growers making fertility decisions should consider using a reputable soil-testing laboratory. Professional laboratories use established analytical procedures and can often provide interpretations and fertilizer or lime recommendations based on the crop being grown. Commercial growers and gardeners making significant fertility decisions can benefit considerably from laboratory analysis.

Is a Soil Fertility Test the Same as a Soil Health Test?

 

Not exactly. A traditional soil fertility test primarily evaluates chemical characteristics related to nutrient management and pH. Soil health is broader.

Physical
Soil structure, water infiltration, compaction, and other physical characteristics.
Chemical
Nutrient availability, pH, organic matter, and other chemical characteristics.
Biological
Biological activity, nutrient cycling, and other soil functions associated with living organisms.

Some laboratories offer soil-health testing packages in addition to conventional fertility testing. A standard fertility test remains an extremely useful management tool, but no single measurement provides a complete description of everything occurring within a soil.

What Is Organic Matter and Why Does It Matter?

 

Soil organic matter consists of plant and animal materials at different stages of decomposition along with materials associated with soil organisms.

Organic matter is connected with many important soil functions, including nutrient retention and cycling, soil structure, water-holding characteristics, and biological activity. Organic matter levels naturally vary considerably among soils, climates, and production systems, so a number should be interpreted within the context of the soil and region rather than assuming one percentage is ideal everywhere.

Does Good Soil Eliminate the Effects of Bad Weather?

 

No. Soil management cannot control temperature, rainfall, drought, hail, flooding, or other environmental conditions. Likewise, selecting an excellent variety cannot eliminate every soil, weather, pest, or disease challenge.

Crop performance results from the interaction of many factors. Variety selection, planting date, weather, soil conditions, fertility, irrigation, drainage, pest and disease pressure, pollination, and management practices can all influence the final crop. The goal is not to find one factor that guarantees success. The goal is to manage as many of the factors within the grower's control as effectively as possible.

How Should I Use My Soil Test Results?

 

Start by reading the laboratory's interpretation and recommendations rather than focusing only on whether individual numbers appear "high" or "low."

Depending on the results and crop, recommendations may include:

  • Adjusting soil pH
  • Applying specific nutrients
  • Reducing or eliminating applications of nutrients already present at sufficient levels
  • Changing the timing or rate of fertilizer applications
  • Conducting additional testing when a particular concern is identified

Avoid applying lime, sulfur, fertilizer, or other amendments simply because a general chart recommends them. Amendment requirements can vary according to the soil, crop, laboratory method, and existing conditions. When results are unclear, contact the laboratory, your local Extension service, crop adviser, or another qualified agricultural professional for help interpreting the report.

Should I Keep Previous Soil Test Reports?

 

Yes. A single soil test provides information about the soil at a particular point in time. Keeping reports from multiple years allows growers to monitor trends.

Over time, those records can help answer questions such as:

  • Is soil pH moving in the desired direction?
  • Are phosphorus or potassium levels increasing or decreasing?
  • Is organic matter changing?
  • Are fertility practices maintaining appropriate nutrient levels?
  • Are management changes producing measurable differences?

When monitoring trends, consistent sampling methods become especially important. Sampling the same general area, at a similar time of year, and at the same depth makes comparisons more meaningful.

How Much Does Soil Testing Cost?

 

Testing costs vary by laboratory and by the analyses requested. Rather than relying on a national price estimate, growers should check directly with the laboratory they plan to use. Basic fertility tests are generally less expensive than specialized analyses or comprehensive soil-health packages.

Considering the cost of seed, fertilizer, equipment, labor, irrigation, and other crop inputs, soil testing can be a relatively small investment that provides useful information for making larger management decisions.

How Do I Find a Soil Testing Laboratory?

 

Testing services vary by state. A good starting point is your state's land-grant university or Cooperative Extension service. Some universities operate their own soil-testing laboratories, while others provide information about reputable laboratories serving their region.

When selecting a laboratory, growers should consider whether the laboratory:

  • Uses recognized analytical procedures
  • Provides interpretations appropriate for their region
  • Offers recommendations for the crops being grown
  • Clearly explains sampling and submission procedures
  • Offers the specific analyses needed

Using the same reputable laboratory over time can also make long-term comparisons easier because testing methods and reporting systems can differ among laboratories.

The Bottom Line

 

Successful crop production is rarely determined by one factor. You can select an outstanding variety and still encounter difficult weather. You can have favorable weather and still experience disease or insect pressure. You can provide excellent irrigation and management, but the crop still depends on the soil surrounding its roots.

Good seed is an important part of producing a good crop, but it is only one part of the production system.

Understanding your soil gives you another piece of information that can be used to make better decisions. Soil testing cannot guarantee a successful crop, but it can replace some of the guesswork surrounding fertility and pH with actual measurements and science-based recommendations. Whether you manage a backyard garden or hundreds of acres, taking the time to understand what is happening beneath the surface can be an important part of preparing for the season ahead.

For More Information, Please See Links Below:

 

Soil conditions and testing recommendations vary by location, crop, and production system. These science-based resources provide additional information on soil testing, fertility, nutrient management, and soil health.

→  Soil Health, USDA Natural Resources Conservation Service
→  Soil Health Testing, USDA Natural Resources Conservation Service
→  Nutrient Management, USDA Natural Resources Conservation Service
→  Soil Testing, Penn State Extension
→  Extension Soil Testing Laboratory, University of Florida IFAS Extension
→  Soil Testing and Plant Analysis, University of Georgia

For recommendations specific to your location, growers can also contact their state Cooperative Extension service, land-grant university, soil-testing laboratory, or qualified crop adviser.

Why, When & How to Test Your Soil

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