“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:
Chemical Indicators
- 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.
Biological Indicators
- 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.
Physical Indicators
- 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.
Digging In
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.