Soil compaction is a global issue that has resulted in reduced crop yields of between 25 and 50 percent in North America and Europe. This problem costs the US economy about US$1.2 billion every year.
The adoption of mechanized farming has been a significant contributor to this issue. This article will offer an overview of the problem, causes, detection, and how to manage and prevent it.
What is Soil Compaction?
What is soil compaction? Soil compaction is the reduction of space between soil particles after a heavy load passes on the soil surface. It can be caused by a variety of things such as heavy farm machinery, animals or regular crop production.
When compaction happens, the air between the soil escapes and the soil grains get closer to each other. When the soil is wet, this process is quickened due to availability of lubrication. Moreover, when the soil has minimal organic matter, it is more exposed to compaction since it does not create strong aggregates.
Negative Effects of Soil Compaction on a Garden
1. Root Growth Inhibition
Soil compaction contributes to the restriction of root growth and impacts the mechanical resistance to the development of roots. Compaction reduces the size and number of large pores called macropores. Therefore, roots will not find pores with a diameter bigger than that of the roots’, which allow roots to grow freely, with no mechanical resistance.
Because roots will not be able to grow beyond certain layers of soil, they spread horizontally. This is referred to as ‘pancake’ root development.
2.Lack of Water & Oxygen
Soil compaction limits the downward movement of water through the soil. Hence, the water in your garden saturates in the upper layers, and roots cannot get access to oxygen.
3. Lack of Nutrients
Moreover, the lack of air in the soil leads to the lack of plant nutrients like manganese and nitrogen. Denitrification can result in great loss of nitrogen in the form of nitrogen gas and nitrogen oxide to the atmosphere under anaerobic conditions. Hence soil compaction can decrease the levels of nitrogen in the soil.
The absorption of potassium by the roots of your plants takes place in a process requiring cellular respiration. But if there is no oxygen in the soil due to compaction, the potassium will not be absorbed by the root membrane.
Diagnosis of Soil Compaction
So, how do you determine that the soil has been compacted? There are a few ways that can help you in making this diagnosis. But these methods are relative, and you need to compare the results with areas where compaction does not happen, and soils are similar.
1. Shovel or Hand Probe
The shovel or hand probe method assists you in determining compaction through the resistance you face when trying to penetrate the soil. The technique assists you in detecting dense soil layers that can resist root growth or penetration.
A hand probe refers to a steel rod that you push through the garden soil with your hand. You will detect compacted soil layers when you experience a lot of resistance as you try to push through the soil. The resistance will reduce once you are past the compacted layer.
Do you want to make a hand probe? You can create one from heavy-gauge fencing wire or steel rod that is about 40 cm long. Loop one end of the wire or steel rod into a handle.
2. Visual Observation
You can detect soil compaction by observing the soil in your garden. So, dig a hole that goes beyond the root layer. Then use a knife to assess the resistance of the soil and the rooting pattern. Keep an eye on areas with high resistance and check if they coincide with minimal root growth.
This assessment will assist you to detect the compacted layer. This is because the soil below and above this layer is less dense than the compacted layer. This layer is easy to see as it has a blocky appearance. It is a horizontal layer that takes place from 10 to 40 cm deep in the soil.
3. Cone Penetrometer
A cone penetrometer operates like a hand probe. However, it does more by measuring the force needed to penetrate the soil layer. The device is pushed inside the soil by hand at a steady speed. Then the device’s gauge will measure and record the force needed for soil penetration at a particular depth. The force is measured in kilopascals (KPa) or megapascals (MPa).
This information will be kept in a data logger, and you can download it to assess the density of the soil. Generally, the growth of your plant roots will be restricted when the penetration resistance is more than 1.5 MPa. Severe restriction takes place at a force of over 2.5 MPa.
Subsoil Compaction Management
1. Growing Vigorous Pasture and Crop Rotation
To reduce soil compaction in the long run, crop rotation is essential. When the crop rotation is diverse, there is stability and creation of soil aggregates. Be sure that the crops include both fibrous-rooted and deep-rooted plants.
2. Changing the Yearly Tillage Depth
This method will prevent soil compaction caused by tillage, and that occurs below the regular working depth of the main tillage implement. The depth of tillage decreases when the soil is wet and increases when the soil is sufficiently dry to shatter a compacted soil layer. A Roto-Tiller is an ideal tillage implement in this case.
3. Deep Ripping
You can use robust tynes to break the hardpan of the soil to a depth of between 20 and 40 cm. Do this only when the soil is between dry and moist and shatters at the ripped depth. Be sure to operate a few centimeters below the compaction zone to save energy and prevent deeper compaction.
Keep in mind that soils with heavy texture can experience re-compaction by machinery.
How to Prevent Soil Compaction in a Garden
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