Consequences of compaction. Under the influence of microbial activity, soil particles bind into generally stable units called aggregates (Figure 7). Heavy equipment and tillage implements can damage these and reduce soil structure.
With an increase in the level of compaction, the amount of water held at a high soil matric potential decreases, whereas the amount of water held at a low soil matric potential increases. The shift in water-retention-characteristic curves reflects a change in the relative proportion of soil pores.
Structural degradation of the soil most commonly refers to compaction, the compression of soil particles so that the space between them is diminished (especially large pores), but can also refer to the lack of cohesion that occurs in sandy soils.
Compaction reduces yields:
Compaction is a significant factor influencing crop yield. Barriers to root growth restrict access to water, air and nutrients, reducing yield by more than 50% in many crops, and causing a total write-off in severe cases. Excessive runoff and erosion can also result.
As an example 1m3 in the ground may become 1.2m3 loose which in turn may become 0.85m3 after compaction (20% swell, 15% shrinkage). SF=1.2, DF=0.15.
Soil compaction can influence plant height by preventing normal root development. This is most detrimental if it's shallow compaction (6 to 8 inches). If timely rains don't soften the compacted layers so roots can penetrate the soil, plants will be stunted, and have fewer fine roots and less overall root mass.
During Compaction
If you make too many passes in a single direction with your compaction equipment you can over compact the soil. Over compaction will actually lower soil density and cause unnecessary wear to the machine. Always check the work surface before beginning soil compaction for dangerous inclines or declines.
Adding compost to your soil is one of the best ways to combat compaction. As organic materials decompose, they attract soil organisms that naturally aerate the soil through creation of pore space.
Soil compaction is defined as the method of mechanically increasing the density of soil. In construction, this is a significant part of the building process. If performed improperly, settlement of the soil could occur and result in unnecessary maintenance costs or structure failure.
Loss of large pores between aggregates is particularly harmful for fine- and medium-textured soils that depend on those pores for good infiltration and percolation of water, as well as air exchange with the atmosphere. Although compaction can also damage coarse-textured soils, the impact is less severe.
While soil degradation is a natural process, it can also be caused by human activity. In the last few decades, soil degradation has been sped up by intensive farming practices like deforestation, overgrazing, intensive cultivation, forest fires and construction work.
However, tillage has all along been contributing negatively to soil quality. Since tillage fractures the soil, it disrupts soil structure, accelerating surface runoff and soil erosion. Tillage also reduces crop residue, which help cushion the force of pounding raindrops.
The impact of individual raindrops can destroy soil aggregates which could result in erosion. Erosion most often occurs on slopes, bare soil, and near downspouts and other places in the landscape where water rushes onto or overland. Storms and extreme high tides can cause erosion along shorelines.
(1986) found that compacted soils resulted in: (a) restricted root growth; (b) poor root zone aeration; and (c) poor drainage that results in less soil aeration, less oxygen in the root zone, and more losses of nitrogen from denitrification. Subsoil tillage has been used to alleviate compaction problems.
In simple terms, when we say a soil sample has achieved 95% compaction, it means that the compacted soil has reached 95% of its maximum possible dry density as determined by a Proctor test. Proctor testing is a test performed in the laboratory that compares the density of a soil sample to various moisture contents.
But sand isn't perfect. There are some downsides to consider: Not great for foundations – Sand lacks the dense compaction you need for structural foundations to bear loads. Gravel or concrete would be better options.
When the soil is weak at depth, compaction can result from vehicle traffic, and it is generally harder to reverse than compaction at the surface. Some soils may naturally return after tillage to a compacted state that will significantly impede root growth.
Luckily, this can be done fairly easily just by covering the soil with organic material such as fall leaves or woodchips. And if you've got a bunch of grass or other plants you don't want anymore, just add a layer of cardboard first before you add the organic material.
1 Aeration creates holes down into the soil to alleviate compaction so air, water and nutrients can reach grass roots. Deprived of their basic needs by compacted soil, lawn grasses struggle in stressful situations, such as heat and low rainfall, and lose their healthy, rich color.
Artificial drainage can help increase the number of trafficable days on poorly drained soil. Keep axle loads below 10 tons. Subsoil compaction is caused by axle load and is basically permanent. To avoid subsoil compaction, keep axle loads below 10 tons per axle--preferably below 6 tons per axle.
Compacted soil has its density increased and its pore spaces reduced. This has the result of decreasing the ability of water to infiltrate through the soil into the ground. This creates surface runoff that can carry pollution, creates standing water for mosquitoes, and increases flooding.
As water builds on the surface, more and more pressure is applied to the soil. For each foot of water, 2.31 pounds per square inch is applied to the soil particles, and over time this can start to cause those void spaces to collapse. That collapse in void space is compaction.