Soil isn’t just dirt. It’s a living archive of nutrients, biology, and chemical interactions that shape every crop season. Soil testing is how we decode that archive. But what exactly are we testing for, and why does it matter?

Soil Testing for the Macronutrients That Power Plant Life

When it comes to feeding the soil and fueling plant growth, five elemental heavyweights rise to the top. These macronutrients are the backbone of biological productivity, each playing a distinct role in the symphony of photosynthesis, root development, and resilience.

• Nitrogen (N) Nitrogen is the lifeblood of leafy growth. It fuels chlorophyll production, protein synthesis, and that lush, verdant vigor every grower craves. But too much? You’ll get all leaf, no fruit.
• Phosphorus (P) Phosphorus drives root expansion, seed formation, and energy transfer. It’s the underground strategist, helping plants establish strong foundations and reproductive success.
• Potassium (K) Potassium regulates water use, strengthens cell walls, and activates enzymes. It’s the plant’s immune system booster, enhancing drought tolerance, disease resistance, and overall stamina.
• Calcium (Ca) Calcium fortifies cell walls and supports root and shoot development. It’s essential for nutrient transport and cellular communication, especially in fast-growing tissues.
• Sulfur (S) Often overlooked, sulfur is vital for amino acids, enzymes, and chlorophyll. It’s a key player in protein formation and flavor development (hello, pungent brassicas!).

Why Soil Testing for These Five Macronutrients Matter

Together, these five macronutrients form the elemental toolkit for regenerative growers. They’re not just nutrients, they’re strategic levers for soil health, crop quality, and climate resilience. But just because they’re in the soil doesn’t mean they’re in forms that are available for plant uptake.

Nitrogen comes in many forms. Testing gives you an indication of what quantity of N you have in the soil that will mineralize around your crop plant roots. There can also be a lot of phosphorus in your soil, but not all of it will be available for plant uptake. Soil pH determines the form of phosphorus available to your crops. In acidic or neutral soils, it’s dihydrogen phosphate (found in MAP). In alkaline soils, it’s hydrogen phosphate.

It’s important to know that most soils have an abundance of phosphorus, but it’s in forms that are unavailable for plants. With the addition of microbes, especially phosphate-solubilizing microorganisms (PSMs), you can access the soil phosphorus and save a lot of money on phosphorus fertilizer.

Potassium, calcium, and magnesium all compete for plant root real estate. They’re all necessary, but in balance. Yield is affected when potassium is deficient. Optimum root development is tied to calcium. Testing for calcium determines lime needs and whether calcium is balanced with magnesium and potassium. Calcium affects pH, base saturation, and cation exchange capacity (CEC), so it is more important than we tend to think.

Sulfur is essential for amino acids, enzymes, and chlorophyll processes. It’s prone to leaching, and sulfur deficiencies are increasing worldwide. Wheat, canola, and legume plant health and yields are dependent on the right amount of sulfur.

Regular soil tests don’t measure total nutrient content. They measure plant-available forms, which are the ions roots can actually absorb. This distinction is critical for making informed decisions about fertilization and biological amendments. A new test we are using is the TND test (Total Nutrient Digestion) to give us the total nutrients in the soil so we know what is in the soil makeup for release.

It’s not just about the nutrients plants need in large quantities. Your crop won’t reach its highest potential without the micronutrients, and testing for them is just as important.

Soil Testing for the Small but Mighty Micronutrients

Micronutrients like zinc, boron, manganese, copper, iron, and molybdenum are needed in trace amounts but can make or break a crop’s performance. Deficiencies often show up as subtle symptoms—stunted growth, chlorosis, poor fruit set.

Soil tests can reveal hidden imbalances, especially in high-pH soils where micronutrients get locked up.

Remember to Measure Soil Biology in Your Soil Test Regimen

Biological tests look at:
● Microbial biomass
● Fungal-to-bacterial ratios
● Enzyme activity
● Respiration rates

These indicators show how alive your soil is and how well it can cycle nutrients, break down residues, and support root symbiosis. Tools like the Haney test or PLFA analysis offer insights into biological health.

The Soil’s Chemical Parameters Influence Nutrient Availability

Soil is an interconnected, living, dynamic set of relationships. The microbes, nutrients, plant roots, sun, air, and water are some of the factors that determine soil and plant health.

● pH: Influences nutrient availability. Most crops prefer 6.0–6.8.
● CEC (Cation Exchange Capacity): Measures the soil’s ability to hold nutrients.
● Base saturation: Shows the balance of calcium, magnesium, potassium, and sodium.
● Electrical conductivity (EC): Indicates salinity levels.

These metrics help you understand how nutrients behave in your soil and whether amendments will be effective. Though we talk about acid or alkaline soil and the base saturation of nutrients, none of these are fixed. Even the CEC of a clay soil can be changed with enough organic matter. Some are more easily changed than others, but anyone who’s grown a hydrangea (and wanted blue when it was pink, or had a purple bloom) knows how pH affects plants and how it can be manipulated.
That interconnectedness isn’t just in the realm of chemistry; it’s also about the physics of soil.

Physical Properties: Texture, Structure, and Water

Sandy, silt, clay, or loam, or some mix of them all, impact the physics of your soil and also the chemistry and biology. A clay particle is 25 times smaller than a sand particle and holds a boatload of nutrients and water. But because it tends to compact, it holds onto those nutrients tightly. Sand, on the other hand, is so porous that nutrients and water just flow right through it. The nutrients aren’t held for the plants, and the water isn’t available either.

● Soil texture: Sand, silt, and clay ratios affect drainage and nutrient retention.
● Bulk density: Indicates compaction and root penetration potential.
● Aggregate stability: Reflects soil’s resistance to erosion and crusting.

These are often assessed visually. You can also get a penetrometer and test for compaction on site. Just push a rod into the ground and see how much push back you get from the soil. This is a valuable test to see how regenerative farming practices with cover crops and no-till have decreased the amount of compaction in your soil. Aside from agriculture, architects and builders are always interested in testing for the physical properties of soil, for obvious reasons.

Interpreting Your Soil Test Results: It’s All Connected

Soil testing isn’t just about numbers, it’s about relationships. A high phosphorus level might not mean availability if the pH is off. A good nitrogen reading might be misleading if microbial activity is low. The best soil tests integrate chemistry, biology, and physics to give a holistic view.

Soil testing is the art of listening to the land. It’s how we move from guesswork to stewardship, from inputs to insight. On our blog, we dig into how to take a good sample in the fall and use it to plan for a resilient, productive next year.

In the meantime, be sure to schedule your soil testing for macros, micros, and biology for this fall. Contact us and we can explain what those tests mean and how you can prepare for next spring. We’re here to help you succeed. When soil speaks, we listen.