Soil sampling is a key part of understanding soil health. Work with your agronomist or SHP Field Manager to determine the best sampling and testing plan for your farm, and visit https://www.soilhealthpartnership.org… to learn more.
“You can’t manage what you don’t measure.” Which is why soil sampling is a critical tool when it comes to measuring your soil health. Soil test results don’t just reflect nutrients; they can also paint a picture of the biological and physical properties of your soil to provide the best roadmap for your cropping season.
When do I measure soil samples?
SHP typically collects soil samples in the spring after the ground is workable but before planting. Sampling occurs at the same time each year to minimize the effects of weather and seasonal movements of mobile nutrients. Seeing as how most of the US is or will soon be taking advantage of available days for planting, now is a great time to start planning to get your soil samples collected.
How do I complete my soil sampling?
SHP has an in-depth soil sampling process that we follow for growers in our program. You can also work with your local agronomist, who can assist you in completing your soil sampling accurately. It is important to follow sampling best practices to ensure you are measuring “apples to apples” over time. Some soil indicators can change very quickly, while others change over a long period of time. Having accurate sampling data will help guide you in planning this year’s fertilization efforts and future crop rotations.
There is some freedom in choosing how to pull soil samples. Some farmers pull from a 0-6-inch depth while others choose a 0-8-inch depth, but the name of the game is consistency. How you choose to pull soil samples should be done the same way year after year to provide the most accurate and robust set of data.
What will I be measuring?
There are multiple indicators measured when soil cores are pulled out of the ground. It is important to remember soil health is complex and dynamic, which means healthy soil can look different in different regions and cropping systems. A number of different soil health indicators can be useful for tracking how the soil responds to management and measuring soil health in the field and in the laboratory. Here is an idea of what indicators are primarily looked at:
- pH – Optimal pH (between 6 and 7 for corn, soybeans and wheat) is critical for crop growth.
- Primary Macronutrients – N, P and K are all essential macronutrients. Crops need sufficient quantities of these in order to grow and thrive.
- Secondary and Micronutrients – Secondary macronutrients like Ca, Mg and S, and micronutrients like Mg, Fe, Mn and Zn are also critical for crop growth, but in smaller quantities.
- Soil Organic Matter – Organic matter influences water holding capacity and contains nutrients that can be broken down by bacteria or fungi to make them available for growing plants.
- Soil Protein – Nitrogen contained in soil organic matter is primarily found in soil proteins.
- Active Carbon – A measure of the food stock available for microbes, which promotes nutrient availability and cycling.
- Respiration – Measuring the CO2 produced by microbes allows us a look into the microbial activity in your soil.
- Soil Texture – Inherent soil properties like soil texture cannot be changed through management practices, but soil texture impacts management practices that fit your operation.
- Available Water Capacity – Water capacity depends on soil texture, but can be impacted by soil organic matter and soil aggregation amounts (both can increase water holding capacity).
- Aggregate Stability – Soil aggregates are held together by root exudates, soil fungi, and inherent soil properties. Reducing tillage creates environments for “biological glues” to improve stability.
- Bulk Density – High bulk density soils have less pore space, leaving less room for air and water needed for root growth. This can also be an indicator of soil compaction.
With soil sampling, start early, be consistent and analyze data over time. While inherent soil properties and cropping systems are different across regions, you can use soil sampling results both to create your future cropping plan and to support your soil health strategy. For more resources, check out SHP’s soil sampling process.
SHP collects soil health and soil nutrient samples on working farms within the SHP network and works with various partners and service providers, including agronomists, soil samplers, and soil laboratories. This process is creating an in-depth data set to support farmers’ decisions and to understand changes in soil health over time.
SHP’s soil sampling process
Overview of the Process
In early spring, SHP assembles and mails soil sampling kits to the soil sampler, which may be an SHP field manager, an agronomist, or a soil sampling company. Each kit contains the materials and information necessary to pull the soil samples: a map of the field and sample points, barcode labels that correspond to the samples to be pulled, bags to hold the soil, and shipping materials to send the samples to the soil laboratories. Samples are shipped directly to the lab, where they are tested and the data is returned to SHP to analyze before sharing with the farmer.
- Soil sample kits contain the materials necessary for pulling the samples out in the field, labeling them properly, and shipping them to the appropriate lab. Samplers supply their own soil probe and buckets.
- Each kit is customized for each field in the SHP program. Barcode labels are printed and sampling bags are counted out each year to meet the needs of each site. This helps guarantee a high level of data quality across the SHP network.
- All kits and samples are tracked throughout the process to ensure timely results.
- Soil samples are typically collected in the spring, after the ground is workable but before planting. Sampling occurs at the same time each year to minimize the effects of weather and seasonal movements of mobile nutrients.
- Using the map and shapefile of predetermined sample points, the soil sampler uses a GPS to navigate to sample points.
- For soil nutrient sampling, the sampler uses a soil probe to take 15 soil cores in a 30-foot diameter circle around a sample point to a 6-inch depth. For each soil core, the sampler separates the core at the 2-inch mark to collect soil that represents the 0- to 2-inch depth and the 2- to 6-inch depth. SHP strip trials are sampled for soil nutrients on a 1-acre grid pattern across the field, and SHP side-by-side trials have 1-3 samples for each management system.
- For soil health samples, the sampler also pulls soil cores on a 30 ft. diameter circle around the soil sample point to six inches. In an SHP strip trial, the sampler combines the soil from all soil sample points within a strip to create a composite soil health sample over two or more soil sample points. SHP side-by-side trials have 1-3 samples for each management system.
- For every sample, the soil sampler bags soil and adheres a barcode that tells SHP and the lab where the sample was pulled and what type of analysis it will be getting.
- Samples are sealed in respective bags, boxed up, and sent to the lab.
- Soil nutrient samples are analyzed for macro- and micronutrients, including phosphorus, potassium, sulfur, zinc, iron, manganese, copper, calcium, magnesium, sodium, boron, and aluminum, along with soil organic matter, pH and buffer pH.
- Soil health samples are analyzed for soil carbon, respiration, active carbon, aggregate stability, available water capacity, and ACE soil protein.
Soil sample results are returned to the farmer after analysis and incorporated into the SHP dataset. The farmer may use the sampling results to make management decisions or track progress over time. However, sampling for soil health indicators is still a relatively new process, and indicators may change slowly with management changes or be affected by sampling and field conditions in a particular year. SHP encourages farmers to look at longer-term trends in sampling as we contribute to a broader effort to understand soil health.
Soil sampling at-a-glance
The agronomist or soil sampler will:
Navigate to the field's sampling points with GPS.
Separate each core at the 2-inch mark to create two samples for 0-2 inches and 2-6 inches.
Bag each sample and adhere a barcode that marks the location and type of analysis.
Take 15 soil cores in a 30-foot diameter circle around a sample point to a 6-inch depth (using a soil probe).
Follow the soil sampling instructions for that particular field trial type.
Seal samples in respective bags, box up, and send to the lab.
You can find a print version of this informational resource by clicking the button below.
Find Out More
Learn more about soil sampling and the soil health indicators SHP is evaluating.
Healthy soil is the foundation for productive crops and a resilient farming system. When it comes to building soil health, we often talk about the physical and chemical properties of soil – things like soil texture, aggregate stability and soil organic matter. There is a third component of soil health, though, that is highlighted less frequently: the biological component.
At its most basic level, soil is made up of weathered rock material, water, air, and the remains of decomposed plants and animals. Beyond that, the soil is an entire functioning ecosystem full of life! In just one handful of soil, there can be billions of microorganisms, including some you’re probably already aware of, like bacteria and fungi.
Other living organisms in the soil can be classified as invertebrates. An invertebrate is simply an organism that does not have a backbone. Some common soil invertebrates include mollusks, earthworms, arthropods (i.e., insects, spiders and crustaceans), and nematodes. Soil invertebrates living beneath the soil surface may be harder to detect, but by familiarizing yourself with the most common invertebrate groups, you can be sure you won’t underestimate their impact on soil health and agriculture.
Arthropods and Earthworms
The role of arthropods and earthworms in agriculture is well-established. Arthropods, at the soil surface and beneath, are great decomposers and nutrient cyclers. Arthropods that feed on plant residue help to build soil organic matter and can impact soil fertility. Soil-dwelling arthropods can be pests (e.g., cutworms or white grubs), but they can also help to control pest populations. For example, ground beetles and spiders are arthropod predators that are often encountered in fields.
When earthworms move through the soil, they create channels that can help improve soil drainage. Earthworms also enhance soil structure and nutrient cycling through their movement and feeding habits. Scouting for earthworms is fairly simple and can be done by counting the number of earthworm middens on the soil surface. An earthworm midden is a small pile of plant material and worm castings (worm poop!) that can be found at the entrance of a worm burrow. The photo below shows five earthworm middens in a no-till field. Click on the link below the photo for more information.
Credit: Sjoerd Duiker via No-Till Farmer
Nematodes – or microscopic roundworms – are lesser-known organisms in the soil. Plant-parasitic nematodes can be agricultural pests that impact plant health and yield by sucking out the contents of plant cells using piercing, needle-like mouthparts. This type of nematode can also vector plant diseases, such as tomato mosaic virus. There are also beneficial nematode groups that are present in healthy soils, such as bacteria feeding, fungal feeding, and predatory nematodes.
Nematode feeding damage is often misidentified as a nutrient deficiency in crops; plant symptoms – such as chlorosis, stunting, and wilting – are common examples. While some nematodes, like Soybean Cyst Nematode, can be visible on plant roots, most nematodes will require positive identification through a soil sample. When soil sampling for nematodes during the growing season, use a soil probe to sample 6-8 inches deep and sample at the base of the plant in the root zone. If sampling outside of the growing season, fall is the best time for detecting nematodes because populations will be at their highest.
Some plant-parasitic nematodes are very common and can be found in nearly every soil type or cropping system (root lesion and stunt nematodes [see picture below], for example). Generally, these nematodes will rarely cause economic harm to crops. Some nematodes, however, are more specific to a soil type or to the crop they are attracted to. Two examples of harmful plant-parasitic nematodes are Soybean Cyst and Corn Needle (see picture below) Nematodes.
The head of a Corn Needle Nematode. This nematode feeds almost exclusively on corn roots and the economic threshold is just 1 or 2 individuals in 100 CC of soil (about a handful of soil).
Stunt nematodes are plant-parasitic nematodes that feed on field and vegetable crops. The economic threshold for stunt nematodes varies by crop and soil type, but is 100-200 individuals in 100 CC of soil (about a handful of soil) in corn.
The soil is a living, functioning ecosystem full of organisms you can and can’t see. Microscopic or not, these organisms can have a big impact on your productivity. The next time you’re out in the field, keep an eye out for signs of earthworms and other invertebrates that can be seen with the naked eye. And, if you are interested in learning more about soil invertebrates on your farm, reach out to your SHP field manager or your local agronomist to explore scouting and soil sampling options.
Jason is the third generation in his family to farm this land. After working in the corporate world, Jason had the opportunity to buy out his uncle and began farming the 2,500 acre farm in Bloomington-Normal, Illinois full-time in 2003.
The Lay farm grows a rotation of corn and soybeans. For the last nine years, Jason has utilized strip tillage for his corn acres. He added no-till on soybeans in 2011. Jason has also added cover crops to his practices, primarily using rye grass, and occasionally oats and crimson clover. He currently has 200 acres in cover crops.
Increased testing is one of the biggest improvements Jason has made in his farming practices—testing soil and stalk nitrate levels. Jason also uses Variable Rate Technology to precisely target what his soil needs in nutrients and when.
“I am personally impressed with the partners that have come together as part of the Soil Health Partnership. Corporate partners, conservation partners and farmers—all working together toward the same goals. I plan on farming for a long while, and we have to be smarter as an industry how we do things. I can help bring about that change by adopting new practices and setting an example for others to follow.”
Kirk and Tiona Kimble are the fifth generation farming their 2000 acres in Chillicothe, Illinois. They are invested in preserving this family heritage for their three daughters, all of which help on the farm today.
Kirk has used numerous covers and combinations through the years: cereal rye, annual rye, vetch, oats, radishes, sunflowers and sun hemp. He puts a cover crop on every acre.
“I know I have my topsoil and it isn’t washed down the river. It’s a justifiable cost,” he said.
Kirk also practices no-till on every acre. When Kirk began farming, he tried no-till to save money by not purchasing more equipment, and he liked the results. With the big rain events occurring more frequently, Kirk says it just works well on his land for keeping erosion at bay.
He soil tests regularly, and depending on the results, does either variable rate or blanket rate application of nutrients. He does not do fall application of nitrogen.
“I believe in the practices that I have implemented, but the Soil Health Partnership is documenting them scientifically,” said Kirk. “I like seeing what is happening in my soil, year over year, and understanding how I can make it better. I like being part of a group that is promoting soil health and conserving our soil resource.”
Understanding the health of a particular soil may also help explain other things that are happening in that field. In our area, a rainfall event of three inches or more at some point throughout the summer is not uncommon. But what’s more important than the rain itself is what happens to the rain once it reaches the soil.
Taking a drive to look at your fields will tell part of the story. Did that rainwater runoff the surface, stay on the surface to create a puddle or did it soak into the soil pores? This ability for soil to take up water and allow movement within the soil profile is how the National Resource Conservation Service (NRCS) defines infiltration.
The infiltration of your soil can be affected by many factors and how water infiltrates your soil can be even more complicated. What if there was a way to understand where water goes and how healthy your soil is by using a basic infiltration test? There are kits available to get highly accurate tests that can translate across many fields, but for our purposes, let’s use supplies you probably have on your farm.
A shovel is the number one tool that I use when looking at soil health. Just digging up 6 inches of soil can tell you about the history, structure, and drainage ability of that soil. Does the soil crumble between your fingers or does hold together? Are there any hardpan layers that may have been caused by tillage? We can learn so much by digging into the soil.
That structure within the soil directly affects how water is either absorbed or runs off during rainfall events. We are able to compare different soils and how they are affected by rainfall with an infiltration test.
- Rubber mallet
- 2 PVC or Steel rings with 6 inch diameter
- 2 water containers filled with 444 mL of water
- Plastic wrap
To get started, figure out what your goals are and which soils you want to compare. Start on one soil type and pound the first ring in with the mallet halfway into the soil. It works best to pre-measure the rings and put a mark on the halfway point to signal how far the ring will go into the soil for the test.
- Start by pounding your ring in with the rubber mallet. If the ground is on the harder side, a board across the top might help. Pound the ring halfway until you get to your mark.
- Place plastic wrap inside of the ring. This will help prevent splash effects that could happen when pouring in your water.
- Take your pre-measured 444 mL of water and pour into the plastic wrap inside the ring. This represents an inch of rainwater.
- Start your timer as you slowly pull the plastic wrap off of the ring to let the water soak into the soil on the inside of the ring.
- Keep an eye on your ring and stop the timer once the water has completely soaked into the soil. There will be a shimmer on top of the soil. Record the number of minutes it takes for 1” of rainfall. Repeat steps 2-5 a second time to represent a second inch of rainwater.
- Repeat this process for your secondary location. This might be a different field, soil type, part of the field that was managed differently. Be consistent in the process and record 1st and 2nd infiltration numbers to compare.
- Dig up your rings and compare the soil at the bottom of the ring. Did the moisture reach the bottom?
Once you’ve finished your tests, what differences can you pick out between your soils? Is it the difference in tillage practices? Was one of the fields harvested too wet in the fall? Does one currently use cover crops?
A soil that has slower infiltration rates is more likely low in organic matter, more easily has runoff in large rain events, and can hold less water in a drought situation, so what management changes might you make based on your in-field infiltration testing?
Don’t worry about having exactly a 6-inch ring or 444 mL of water for your own in-field testing. At the end of the day, this test is meant to be a learning experience and a great way to compare one field to the next. Make sure you are consistent and continue to use the same tools and you should learn a great deal about your soils!
Soil sampling can be a great step in the pursuit of healthier soils, but it is not always easy to get soil sampling right. The correct procedures yield the best data, and the best data helps farmers achieve the healthiest soil.
But how do you get the best data?
Dr. Nick Ward of Ward Laboratories, Inc. helped farmers understand how to best sample soils on their farm in an April 28 Soil Health Partnership (SHP) Soil Sessions webinar, “Quality in, quality out: the Dos and Don’ts of Soil Sampling.”
Most importantly, Dr. Ward reminds farmers that data is knowledge. The data available from proper soil sampling can impact future fertilizer applications, environmental compliance, diagnosis of problems, and overall sustainability. The question is not should I sample my soils, but how can I best sample my soils.
“You can’t make good decisions without data,” he said.
Farmers have numerous opportunities to make specific choices about how they will collect the soil data from their farms. Soil sample depths vary. Some farmers work from a 0-6” depth and some from a 0-8” depth. Dr. Ward teaches that “constant depth is the most critical thing when we’re out soil sampling.”
Whatever depth you choose, just be sure to be consistent throughout the field and year over year to provide the best data. And when you are thinking about testing before or after tillage, just remember that consistent depth is paramount, so sample the same every year in a way that you feel most confident you are achieving a consistent depth.
Soil sample locations can vary. Many farmers chose to sample in a grid pattern, taking the samples where the lines of the grid overlap. This allows for the sampling of the same exact location over time in order to pinpoint changes in the soil, but some farmers choose to sample more heavily in certain zones or problem areas. Still, other farmers composite sample their fields, meaning they select the areas of the field to sample at random.
“Composite sampling should be doable for just about everybody,” Ward said. “Grid sampling is the most intensive practice, but it’s going to give us our most robust data set to make decisions from.”
Your soil health strategy should inform the decisions you make for how and where to sample. The most important reminder is to always be consistent.
How often should you sample? It will depend on your sampling strategy, says Ward.
“If you do something more intense like multiple zones or a grid sample, maybe doing that every 3-4 years would be a good practice. But if you are not going to build a dense data set spatially across your field, maybe it is more important to take a dense data set in time. So, that’s sampling a composite every year in different spots.”
This one-hour webinar will answer many questions and help farmers really nail down the sampling strategies that could work for their farms and soil health goals, as well as guide them with the return on investment for the effort.
Check out other SHP Soil Sessions here.
- Sample and sub sample numbers, sample depth and sample location
- Tools for successful soil sampling
- Costs to soil sample
- Plant sampling
Soil Sessions is a webinar series by the Soil Health Partnership that provides monthly, in-depth updates on various SHP programs and research findings. Soil Sessions covers a range of topics such as our evolving data insights, how SHP manages and integrates data, our connection to and work with our partners, as well as providing technical information on topics like cover crops, scouting and grazing. To view all SHP webinars, visit our website here.
The Soil Health Partnership (SHP) takes soil sampling and testing very seriously. SHP administers higher resolution grid samples, pulls more depths of soil, and dives deeper into soil health testing than most agronomy specialists. We can do so because this is the focus of our team: giving farmers more data to help make long-term management decisions.
Over our five-year program, we measure and record visual observations through crop scouting and measuring and recording soil properties that can only be understood through soil testing. Typical trials that occur on-farm usually only measure yield. This is where the uniqueness of the SHP program begins to shine. SHP goes more in-depth with the annual soil sample and the bi-annual soil health samples.
What does SHP measure?
- Chemical Soil Sampling: SHP does these tests in much higher resolutions than most agronomy specialists. For most soil samples, you are looking at a zone sample or 2.5 acre grid. Within our research, we are studying these same soil characteristics at a 1-acre grid sample resolution, or even smaller. Most test replicated plots are not this large either. With the larger plot size and higher resolution, we are afforded the opportunity to generate more data and observations throughout every growing season.
- Soil Health Testing: This is where SHP invests more time and goes more in-depth than most trials. SHP looks at soil health on each strip in Partner Fields, usually eight strips per field. We continually track aggregate stability, water infiltration, active carbon, different soil proteins, soil respiration and more. Many farmers are not currently doing soil health tests. More often than not, growers do not know that these kinds of tests exist, what they do, or how to use the data. They require more time and are more labor-intensive to acquire than periodical soil testing. These tests and findings typically do not drive annual decisions, but builds a data set over time. Soil health practices provide long term information on adapting inputs and making amendments to soil and management practices.
Results from these tests are reviewed with SHP on a consultation-based approach. It is not about the here and now. Soil health testing requires a different cadence than the annual cycle that most of us are accustomed to in farming.
Together, we must stay focused for the long term, to not only make sure we acquire the information on soil health annually but also that we know what to do with the information that is collected. Soil health data is beneficial to review each year to understand the ebb and flow of your field, but annual management changes should not be driven by the data.