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Testing the physical properties of the soil before sowing: why is it worth it?

For a farmer, the soil represents a "workplace" that provides both revenue and satisfaction. Understanding the structure of the land in your field and managing its properties can help maintain high fertility levels. Soil quality can be analyzed through various interrelated aspects that affect yield. This article will discuss its physical properties and explain how to test them.

Physical Structure of the Soil

Regarding physical structure, the soil consists of various elements, whose optimal condition leads to high yields. Two critical factors are the lumpy structure and the humus content. The type of soil and the living organisms within it (earthworms) are also important.

How to Assess the Condition of Soil Yourself?

Evaluating the physical properties of soil enables informed decisions regarding technological activities and fertilization. How can you assess its condition independently?

Soil Profile Analysis

To independently evaluate the physical properties of the soil, use a spade and conduct careful observations. Dig at least three holes up to 30 cm deep:
- Dig one hole where plant growth suggests poor soil quality
- Dig the second hole in an area presumed favorable for plants
- Dig the third hole in a location undisturbed by crops.

A soil structure profile will be created in the hole dug the width of the spade. It is advisable to take a photo of it (even with your phone) and then carefully analyze the soil structure at your home. What to examine? Observe the size of the soil aggregates, particularly in the upper layer. For plants to absorb the appropriate amount of water, the aggregates should be up to 5 cm wide. Larger aggregates indicate that the soil is too dry, as does the absence of a lumpy structure. Additionally, examine the plant roots—do they spread sideways or go down? If they reach a certain depth and then spread sideways or ascend, it indicates soil compaction at that depth. Look for a plow base or a layer of thin compacted soil and note its depth. In quality soil, pores—cavities where water and air accumulate—should also be visible.

You can use a penetrometer to determine the depth of the plow sole, allowing for proper adjustment of the subsoiler teeth. Additionally, regulating soil pH is crucial.

Dropping soil from a height

A detailed analysis can be conducted by taking a soil sample, preferably with a plant rooted in it, and dropping it from a height of approximately 1 meter. The lump will break into smaller particles. The more particles retained at the root, the more pores are present, enhancing the roots' ability to absorb water. The size of the lumps provides additional insights into the soil structure.

Slamp Test

When using the collected sample, you can perform the slamp test. Place a lump of earth in a strainer immersed in a transparent container filled with water. Once the soil is soaked, empty the contents of the strainer onto a plate. Soil with unstable and poor-quality aggregates will start to merge with the water and, when poured onto a plate, will resemble a mud puddle. Conversely, soil with a stable structure, which implies better water penetration properties, will remain virtually intact. A proper structure will ensure that plants have access to water and nutrients throughout the entire growing season.

Assessment of Soil Grain Size

The structure of soil is influenced by its type; for instance, sandy soils are more compact. To assess soil grain size, rub the cleaned sample between fingers, either dry or wet, or by rolling it between the thumb and index finger.
- Sandy soil: Easily rubbed, does not dirty fingers, and cannot form rollers
- Dry clay soil: Slightly crumbles, dirties fingers; wet clay soil clumps and is sticky, forming a roller with a diameter of 1-2 mm
- Silty soil: Intermediate between sandy and clay soil, forms a roller with a diameter of 4-6 mm.

The number of earthworms in the soil

The number of earthworms in the soil is also an important factor to consider. These beneficial organisms process crop residues, transferring them from shallow layers to deeper ones. Earthworms can produce 200 tons of organic fertilizer per hectare per year. It is assumed that 2 to 4 earthworms should be present in one shovel of earth, although estimating this can be challenging due to their speed and elusiveness. Another measure is 10-20 earthworms per square meter, with fertile soils potentially housing up to a thousand. To gain an accurate understanding of earthworm activity, a complete soil profile—digging a hole up to 2 meters deep and 7 meters wide—is necessary to count their corridors. Alternatively, digging an outcrop on a proportional scale, such as ⅕ square meter, and counting the holes in the scraped soil profile can be effective. A result of around 20 holes on such a surface indicates high earthworm activity.

Testing the Humus Content in Soil

In the laboratory, specific organic fractions can be analyzed to determine the quantity of freshest organic matter, along with young, intermediate, and even 50-year-old humus. This analysis is conducted at District Chemical and Agricultural Stations and includes testing the content of humus or organic carbon. If organic carbon is tested, the result must be multiplied by 1.724 to obtain the humus content. For the other option, no additional calculations are required. It is important to note that an additional 1% of humus in soil equates to 160 tons of stored water and nutrients, as humus can store 800 times more than clay particles. Therefore, knowing the humus content and its structure in the soil is valuable. The increase in humus and improvement of soil structure is influenced by its acidification. Fungi, which bind soil aggregates, are less effective in low pH environments yet crucial for enriching soil with humus—producing 50 kg of young humus from 100 kg of introduced straw. When examining humus content, it is also advisable to test the soil's pH level.

When and how often should soil testing be conducted?

It is optimal to conduct all soil property tests after harvest and prior to fertilization. Avoid testing during excessively dry or humid weather, as this may yield inaccurate results. Soil samples should be analyzed every four years at a minimum. However, given today's unstable climatic conditions that can alter soil properties throughout the year, assessing soil condition each growing season is advisable.

Testing the Physical Properties of Soil – What Next?

By assessing the physical properties of the soil, appropriate agrotechnical treatments can be implemented in the field. For sandy lands, spring cultivation should be minimized. Introducing organic substances that retain water and fertilizer is crucial. Dusty soils with poor structure in the top layer require different treatments, including the use of rollers, while clay soils necessitate separate approaches. Improving soil structure can be achieved by foregoing traditional plowing, utilizing a subsoiler, and employing preparations containing humic acids. To increase the humus content, it is essential to incorporate substantial organic matter, such as leaving straw and plant residues.