Understanding the Different Methods & Importance of Soil Sampling

To get a complete picture of how an agroecosystem is doing, you have to look at what’s happening below the ground. One way to do so is with soil testing, which measures a wide range of soil characteristics and data points, including pH, organic matter, and microbial activity. The process and specific metrics vary depending on which type of soil test is used. When done right, soil sampling can provide a representative snapshot of fertility across an agricultural field–providing growers with critical information to make their best management decisions.

Why is Soil Sampling Important?

Soil sampling is important because it measures a broad scope of chemical, biological, and physical soil characteristics, giving farmers greater insight on the health of their soils and crop systems. One of the most critical elements that testing can reveal is the amount of soil microbial activity.

Also known as “microscopic organisms,” soil microbes perform several complex functions that are essential to crop productivity including:

• Breaking down crop residues
• Cycling nutrients through the soil
• Enhancing water and nutrient uptake
• Stimulating plant growth

Not all microbes are created equal. Fertile soils require a balanced presence of beneficial microbes and an absence or low presence of harmful microbes.

The question of when, where, how deep, and how often you should sample your soil remains a running debate among soil scientists.

There are also several types of soil tests used to analyze the many soil components and properties that may impact crop development.

Measuring Carbon in Soil – Bulk Density & Soil Organic Content (SOC)

As a living system, soil depends on the presence of carbon for a wide variety of chemical, physical, and biological functions.

Carbon measurements are derived from a combination of bulk density and SOC analysis.

• Bulk density tells you the amount of pore space and storage capacity of the soil sample. It is an indicator of soil compaction, calculated of dry weight of soil divided by its volume.
• Soil organic content (SOC) is derived from soil organic matter and plays an integral role in the formation of energy that is usable to plants.

The presence of SOC provides a wide host of benefits, including improved nutrient and water-use efficiency, better soil structure, and reduced erosion.

Well-balanced SOC pools result in:

• Soil structure or tilth for greater physical stability
• Improved soil aeration
• Higher water drainage and retention
• Greater nutrient absorption
• Increased biological productivity of a field
• Increased yield / net productivity
• Higher overall agroecosystem resilience

Changes in SOC generally occur over the span of several years. It is often difficult to track and identify small changes, but a strong soil sampling strategy can help to capture the variation in soil carbon over time.

Rather than taking physical soil samples, many carbon farming programs rely on soil modeling, which calculates soil composition averages for an entire geographic region or zone.

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