SoilOptix® Blog

The Basics of Measuring Soil Fertility

The secret to raising healthy crops is excellent soil. Now, the question is, how do you know if the soil is fertile enough? This needs a soil test. A soil test is the best way to measure soil fertility. When you send a sample to the lab, you’ll get a detailed analysis of the soil nutrients, including any deficiencies. Using an accredited lab or soil analysis technology is always recommended to get the most accurate measurements. However, there are a few easy ways that you can monitor your soil quality while you are out in the field scouting yourself. In the following section of this blog, we’ll provide a few tips and tricks to help you assess your soil quality. Remember, the more detail you have, the more reliable and accurate the results will be.

Soil Structure and Tilth

When the soil is neither too wet nor too dry, dig a hole of 6 to 10 inches deep. Separate an entire section of the soil and break it with your fingers. Determine whether the soil is cloddy, granular, or powdery. Ideally, the soil must have different-sized crumbs that hold the shape even after slight pressure. The crumbs or aggregates break apart only when the ground is too hard.

Why is it important?

As a measure of soil fertility, the soil rich in organic matter will form round crumbs that lead to porosity. Open and porous soil will allow the free movement of oxygen and water. Thus, plants can develop strong and healthy roots.


Plunge a wire flag into the soil at different locations. Mark the depth at which the wire bends. The quicker it bends, the more compact the soil is. A foot or more of easily penetrable soil is perfect.

Why is it important?

Compacted soil inhibits root growth and water availability, and it keeps the earthworms and other vital soil fauna from circulating freely.


You might have learned about the soil’s workability if you have been farming for quite some time. However, the workability will be low if tilling or digging the soil offers cloddy or plate-like clumps. Farmers can measure workability by monitoring tractor fuel consumption. Then, you can simply judge the effort needed to prepare the beds for planting.

Why is it important?

Workable soil allows the water to reach the roots efficiently and is less prone to compaction. If you fail this step, your field is likely to show disappointing results for a lot of other soil tests. When the soil is not easily worked, there could be other problems in the soil that have been there for a while.

Soil Organisms

Measure the animal life in the soil by digging down 6 inches and peering intently into the hole for four minutes. Tick off the species of each organism observed, including the centipedes, the ground beetles, and spiders. Most of the soil organisms spurn daylight. If you gently probe the soil, you shall unearth more shy residents. If the soil organism count is less than 10, this could be a sign that the soil doesn’t have enough active players in the food chain. This is a crucial element in determining soil fertility.

Why is it important?

A thriving population of diverse fungi, bacteria, insects and invertebrates is one of the primary indicators of soil quality. The more that creeps and crawls under your garden, the less opportunity there is for unwelcome pests and diseases. Each level of soil life has a role in breaking down the plant residue and making more nutrients available for growth.


As a measure of soil fertility, when the soil is not too dry or too wet, you must examine the soil surface for earthworm castings and burrows. Dig out 6 inches of the soil and count the number of earthworms squirming on the shovel. Three worms are good, and five are better. The absence of worms could be an indicator that the soil doesn’t have enough organic matter for them to feed on.

Why is it important?

Not only do the earthworms aerate the soil, but the castings infuse the soil with bacteria, enzymes, organic matter, and plant nutrients. Also, it increases the soil infiltration and secretes compounds that bind the soil particles together with higher tilth.

Plant residue

If you have grown a cover crop, you must dig down 6 inches after a month and seek plant matter. Again, the range of organic material is crucial to notice. The presence of plant parts, plant fibres and darkly coloured humus indicate an ideal rate of decomposition.

Why is it important?

Organic matter is one of the most important indicators of healthy and fertile soil. However, plants and other organic materials decompose only when the soil organisms are there to do the work. Any sign of this process is a good sign, but the speed of decomposition is crucial. Quick decomposition is an indicator of soil quality. In poorly aerated soil, the plants break down slowly. You can recognize this condition from a sour scent.

Plant Vigour

Plant vigour is also a good indicator of soil fertility and quality. You must start this test during the active growing season and look for a uniform healthy plant colour and size. The overall health and development must be judged to consider what is normal for your region. One caveat – if you suffered a pest infestation or planted late or there has been a drought, the results will be unreliable.

Why is it important?

Plant vigour indicates soil with good structure and tilth, good water regulation and a diverse population of organisms. It is the best sign of effective soil management and a measure of soil fertility.

Now that you know the best methods to measure soil fertility, you can do the above steps to check soil quality. However, it is better to get help from professionals and send soil samples to an accredited lab to get an accurate soil quality analysis. Contact SoilOptix today to learn about the benefits of high resolution soil analysis.