Soil Compaction Affects Moisture Content, Pore Size Distribution and Ultimately Plant Growth

Soil compaction impacts heavily disturbed reclaimed pipeline corridors leading to severe limitations including reduced crop and native vegetation growth, low fertility, poor soil structure leading to low water holding capacity and availability.  A high degree of compaction that can occur along a right-of-way (ROW) is one of the most significant limitations to revegetation. Soil compaction occurs when disturbed soil leads to  soil aggregates being broken apart into loose fragments.  When replaced during reclamation, soil with a weakened structure is susceptible to compression from repeated movement of heavy machinery and equipment.

What is soil compaction?

Soil porosity and water content of a well-structured and compacted poorly structured soil

In undisturbed soils,  the distribution of pore sizes is determined primarily by soil structure, or the arrangement and geometry of soil particles as they aggregate and become more grouped or clustered together.  Well aggregated soils are comprised of roughly 50% mineral soil and 50% pore space. Pore spaces and connectivity are important for gas and water transport, and water retention properties in the soil.  Pore spaces can be simplified into categories of macropores (> 100 um), mesopores (30-100 um) and micropores (< 30 um). Soil water holding capacity at saturation is governed by the proportion of macropores and soils typically have a higher water holding capacity as the distribution of macropores increases. As the soil dries macropores are drained first by gravity as the adsorptive forces between the water and mineral soil are low. Water is then held by finer meso- and micro- pores that retain water in thin films along the pore edges. These pores can remain saturated even when the soil dries, however, the water retained is often held so tightly to the soil that it is unavailable for plant use.

During soil compaction, there is a decrease in soil porosity and a shift in the distribution of pore sizes compared to off ROW conditions. Macropores become compressed due to their weaker internal structure increasing the distribution of meso- and micro-pores.  At saturation, compacted soils have a lower volumetric water content compared to uncompacted, structured soil since the proportion of macropores in the soil have been reduced. As free water drains from the soil profile the water content is typically greater in the compacted soil. Gravitational forces are unable to overcome the adsorptive forces that retains the water to the finer pore edges and as a result, unsaturated water content in compacted soils can be greater than the undisturbed soils on off-ROW. Although, soil water content may be greater in compacted soils, it is less plant available as plants must exert greater energy to pull the water away from the soil particles. As a result, vegetation can encounter “drought-like” conditions even when soil moisture content is higher, and this can lead to reduced crop yields and native plant regrowth on a reclaimed ROW.

How can I improve soil compaction?

Improving the soil structure and the pore size distribution within your soil can significantly improve post construction reclamation success by increasing plant available water and minimizing plant water stress. There are several mechanical and biological solutions to minimize, mitigate or control soil compaction and improve the soil pore distribution that includes:

Avoidance

The simplest way to minimize soil compaction is to avoid excessive trafficking over the area by using designated travel lanes and controlled traffic.

Cover Crops

Soil Compaction Management – Deep Rooted Cover Crops

Radish and turnip cover crops act as a natural bio-decompaction alternative when mechanical loosening is not feasible such as on steep slopes. Tap rooted species such as these can break up compacted layers and promote the rearrangement of soil particles facilitating aggregation and increasing soil porosity.

Deep Ripping

Soil Compaction Management – Deep Ripping

Subsoiling has been shown to be an effective method to alleviate compaction induced effects on soil properties. Subsoiling works by lifting the soil and allowing it to bend over the shanks, creating cracks or fissures in the soil. This can reduce the soil bulk density and increase macroporosity which increases infiltration capacity, drainage, and water holding capacity.

Soil Organic Matter

Healthy soil for plant growth requires a range of organic matter composition

Maintaining adequate soil organic matter can help stabilize the soil structure and increases its resiliency to compressive forces. In disturbed soils soil organic matter can aid in structural development and aggregation of soil particles.  A range of organic matter that provides easily used components, and more recalcitrant organic is best for long-term management of soil compaction.

 

 

 

 

Duraroot can identify and develop methods to improve compacted soils and improve plant growth on reclaimed pipeline ROW’s. For a free 30 minute consultation reach out to Christina Hebb at chebb@duraroot.com

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