understanding soil compaction - ocean county · slide 2: “the outline for this presentation is as...

“Welcome to today’s ‘Understanding Soil Compaction’ workshop.”

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“The outline for this presentation is as follows:‐We will define and describe soil compaction.‐We will describe the causes of soil compaction.‐We will discuss the effects of soil compaction on soil health, especially changes to the physical and biological properties of soil.‐We will talk about ways that soil compaction can be minimized or managed.‐We will describe ways to assess whether or not soil is experiencing compaction ThisWe will describe ways to assess whether or not soil is experiencing compaction. This includes both observations one can make and using a device known as a penetrometer to measure soil resistance.‐And finally I will describe what I would like to obtain from you (Rutgers Master Gardeners) after today’s workshop.”

Photo Credit(s):Steve Yergeau, Rutgers Cooperative Extension of Ocean & Atlantic Counties

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“When trying to define soil compaction there are two different views to take. One is looking at soil compaction from an engineering perspective and the other is an environmental perspective.”

Photo Credit(s):Wikimedia Commons (https://commons.wikimedia.org/)Steve Yergeau Rutgers Cooperative Extension of Ocean & Atlantic CountiesSteve Yergeau, Rutgers Cooperative Extension of Ocean & Atlantic Counties

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“Soil compaction in engineering is defined as the increase in soil density due to an outside force such as a mechanical compactor or steamroller. This increase in density is due to the loss of air from the soil matrix.

Loose soils do not provide strength and support to loads traveling over them. Whereas, compacted soils have increased strength and provide improved support of loads traveling over them ”over them.

Photo Credit(s):Geotechnical Engineering 101 & More(https://kshitija.wordpress.com/2006/09/29/soil‐compaction/)

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“Many types of construction, such as dams, retaining walls, roads, and building foundations, require additional soil, or fill. This fill needs to be compacted to stabilize soils and improve their engineering behavior since the fill can be of a different soil type and texture from the native soil where these structures are being built. Soil compaction during construction helps to decrease future settlement of the soil, to increase the amount of the stress that a soil can sustain, and to decrease permeability and prevent water damage to the structures ”the structures.

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“Without proper compaction of the soil and fill material, structures will succumb to problems associated with settling or shifting of the soils, erosion or loss of soil due to water seepage. This graphic illustrates some of the results of improper compaction and how proper compaction can ensure a longer structural life, eliminating future problems.”

Photo Credit(s):Engineering Daily – The Basics of Soil CompactionEngineering Daily The Basics of Soil Compaction(http://www.engineersdaily.com/2014/03/basics‐of‐soil‐compaction.html)

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“In engineering, the goal of soil compaction is to ensure the two ‘S’s’: stability and safety.”

Photo Credit(s):Wikimedia Commons (https://commons.wikimedia.org/)

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“We now look at compaction from an environmental perspective. The definition of soil compaction is similar to the engineering definition: it is the increase in soil bulk density due to the loss of air from the soil matrix. The differences are that compaction during construction is intentional and is created quickly. Natural compaction occurs very slowly and is an unintentional result of natural processes.”

Photo Credit(s):Photo Credit(s):Jelusic, P. (2015). “Soil compaction optimization with soft constrain.” Journal of Intelligent and Fuzzy Systems. 29(2): 955‐962.

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“Bulk density is a measurement that indicates the level of soil compaction. The soil sample volume is measured and the soil is allowed to dry, and then gets weighed. It is calculated as the weight of a sample divided by the volume of the soil sample. Usually the weight is measured in grams and the volume in cubic centimeters, so bulk density is expressed as grams per cubic centimeter.

The higher the bulk density the more compacted the soil ”The higher the bulk density the more compacted the soil.

Photo Credit(s):Introduction to Soil(http://www.slideshare.net/andykleinschmidt/introduction‐to‐soil‐science‐presentation)

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“Bulk density can also vary depending on the prevailing land uses in an area. Lands left relatively undisturbed, have low bulk densities and suffer less soil compaction. As lands become more developed and/or managed, construction and management activities can increase bulk density and compact the underlying soils. The construction materials themselves, such as concrete, can be considered compacted.”

Photo Credit(s):Photo Credit(s):Ocean County Soil Conservation District (http://www.soildistrict.org/)

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“Most soil compaction occurs near the ground surface, but repeated activities in a given area can cause compaction to travel down through the soil column and create subsoil compaction, which may occur below the ground surface.

Sometimes, subsoil compaction can occur even though there is no surface compaction.”

Photo Credit(s):Photo Credit(s):Introduction to Soil(http://www.slideshare.net/andykleinschmidt/introduction‐to‐soil‐science‐presentation)

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“Now that we know what compaction is, let’s turn our attention to what causes soil compaction.”


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“Compaction is most often caused by continuous wheel and foot traffic. For agricultural areas, this includes livestock traffic in pastures and fields.

Soil is most susceptible to compaction when soil moisture is at field capacity, which is when about half of the soil’s pore spaces are filled with water and half are filled with air. If there is too much water and the soil is saturated, the soil is too fluid and muddy to compact. If there is too little water and too much air it becomes too difficult to remove the air andthere is too little water and too much air, it becomes too difficult to remove the air and compact the soil. Remember that compaction is the removal of air from the pore spaces.”

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“Here is a graphic depicting the three scenarios discussed in the previous slide. Field capacity is the ‘sweet spot’ condition that makes soil more likely to become compacted. This is the reason why we measure soil moisture/soil water content whenever we take any measurement of compaction.”

Photo Credit(s):Irrigation Management and Water Wise GardeningIrrigation Management and Water Wise Gardening(http://www.slideshare.net/sherylwil/2‐wwg2‐soil‐hydrozone‐irrigation)

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“These are the many ways that compaction can and usually does occur due to foot traffic. Remember that these activities need to occur repeatedly over a long period of time to cause compaction.”


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“Wheel traffic from farm equipment and vehicles can also lead to compacted soils. One of the problems with soil compaction in agriculture is that as farms get larger, the equipment needed to farm the land get larger and heavier. This leads to greater instances of soil compaction.”

Photo Credit(s):Wikimedia Commons (https://commons wikimedia org/)Wikimedia Commons (https://commons.wikimedia.org/)

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“Not all of the wheel traffic comes from agricultural equipment, but also from lawn maintenance equipment in residential and recreational areas. For example, a lawn mower being used for 1 hour drives the equivalent of 20 miles.”


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“Two factors help to contribute to compaction due to traffic: soil moisture and the weight of the load borne by the wheel (or the livestock animal, for foot/hoof traffic). Higher amounts of moisture in the soil have the effect of transmitting the pressure exerted on the soil deeper down the soil column. The graphic on the left shows, with the same weight and tire pressure, that tires can exert pressure further into the soil with increasing soil moisture. The same can be said for a heavier load being carried on the wheels. The graphic on the right shows that with increasing load (weight bearing down on the tires) pressure is exertedright shows that with increasing load (weight bearing down on the tires) pressure is exerted further into the soil.

Also, this applies to livestock and human foot traffic, if you imagine replacing the tires in these graphics with feet, or animal hooves.”

Photo Credit(s):Understanding and Managing Soil Compaction in Agricultural Fields(http://aces.nmsu.edu/pubs/_circulars/CR672/welcome.html)

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“Soils can also have inherent properties that naturally make them more likely to compact. This map shows Ocean County (NJ) and the risk that soils have to being compacted. This risk is determined from factors such as estimated water content, depth to the water table which influences soil moisture, the soil texture, and the amount of sands, silts, and clays in the soil matrix.”

Photo Credit(s):Photo Credit(s):Steve Yergeau, Rutgers Cooperative Extension of Ocean & Atlantic Counties

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“Now let’s take a look at how compaction affects both the physical and biological properties of soils.”


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“As mentioned before, 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 and to pond on the surface, as in the photo seen here.”


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“An uncompacted layer has enough porosity to allow water to pass through it and into the groundwater/aquifer system during rain. Compacted soils become more impervious and prevent water from passing through it, due to the lack of spaces between the soil grains. The water will travel across the landscape, either below the soil or above it as runoff. The pictures above show compacted soils with rain water pooling on the surface.”

Photo Credit(s):Photo Credit(s):Michael Gross, Georgian Court University

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“Because the water travels through the uncompacted soils or over the ground surface, it has the potential to carry away these uncompacted soils through erosion. The looser soils that surround compacted soils are at risk of being washed away.”


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“Soil compaction also causes the penetration resistance of the soil to increase with increasing density. There is little root growth through soil above 300 pounds per square inch (psi), except if there are cracks and macropores in the soil that can be followed by plant roots. The plant roots are unable to develop enough force as they grow to penetrate the compacted soil.”

Photo Credit(s):Photo Credit(s):Wikimedia Commons (https://commons.wikimedia.org/)

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“Compaction affects the ability of plants to take up nutrients and grow. Denitrification (creation of nitrogen gas) can increase in compacted soil. Denitrification occurs best under soil conditions without much oxygen, and the loss of air (and therefore oxygen) due to compaction allows this. Plants are unable to utilize the nitrogen gas directly for growth, as they need the oxygenated forms of nitrogen (nitrite and nitrate). This affects both the above ground leaf growth and below ground root growth. Phosphorus and potassium uptake can be reduced if root growth is inhibited Aerating the soils can help replace someuptake can be reduced if root growth is inhibited. Aerating the soils can help replace some of the air/oxygen that’s been lost due to compaction and help plants grow better.”

Photo Credit(s):Fertilizer Plus – Core Aeration (http://fertplus.com/core‐aeration/)

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“This loss of leaf and root growth affects the overall production of plant material and this can cause problems for agriculture. As can be seen from this graphic, corn yields do poorly under compacted soil conditions. Research has shown that tilling (breaking up and turning over soil) helps to counteract the extent of compaction.”

Photo Credit(s):Soil Fertility and CompactionSoil Fertility and Compaction(http://www.cropnutrition.com/soil‐fertility‐and‐compaction)

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“Organisms that live in the soil can also find that compaction affects their environment. Compaction makes it more difficult to dig through the soil to create burrows and homes. Animals, like earthworms, can’t dig to find food to survive. This has the affect of impacting other organisms higher up the food chain.”

Photo Credit(s):LifeUnderYourFeet orgLifeUnderYourFeet.org(http://lifeunderyourfeet.org/en/soileco/intro/biogeochemistry.asp)

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“The are many ways that one can deal with soil compaction. Compaction can be managed (never eliminated) using any of the following ways:‐Limit or ban the use heavy machinery on wet soils; wait for soils to dry before driving or walking over them.‐Restrict or redirect foot traffic; line paths with stone, mulch, or pavers.‐Aerate the soil to help improve nutrient availability to plants.‐Mechanically break up compacted soils; hand dig or use a tiller to fracture soilsMechanically break up compacted soils; hand dig or use a tiller to fracture soils.‐Remove and replace topsoil; you can also add compost or another amendment to the soil to reduce compaction.‐Create raised beds for plantings.‐Plant deep rooting vegetation prior to compaction creation; plant after compaction occurs.”

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“One plant that has received a lot of attention in the agricultural community is tillage radish, or daikon. This plant grows a long, thick taproot that is able to grow through compacted soils and is used as a cover crop. Tillage radish allows farmers to continue to grow their crops, but also to help manage compaction during that process.”


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“Let’s now discuss some of the outward signs that you can observe to identify where soil compaction may be occurring.”


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“Look for areas that have obvious signs of heavy foot traffic. Areas with exposed soil in continuous pathways, and a lack of vegetation may indicate soil compaction.

Remember that one of the major causes of soil compaction is heavy vehicle and foot traffic.”


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“Even without high foot and vehicle traffic, compacted soils can impede root growth. Look for areas where shallow or surface roots are found, because the roots can’t grow downward through the compacted soils. Also look for areas where vegetation is lacking that are not associated with footpaths.

This may be due to natural properties of the soil that may increase the likelihood of them compacting ”compacting.


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“Areas where water ponds on the ground can indicate where water can’t infiltrate due to compaction.

These could also indicate areas where clay soils are creating a barrier to water. So make sure you look into what types of soils are present.”

Photo Credit(s):Photo Credit(s):Michael Gross, Georgian Court University

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“One method to determine if soil compaction is present, as recommended by the Ocean County Soil Conservation District, is to use a wire marking flag. You push the wire into the soil as far as you can and measure the distance the wire has entered the soil. If less than 4 inches of the wire has penetrated the soil, you can consider the soil to be compacted.”

Photo Credit(s):Ocean County Soil Conservation District (http://www soildistrict org/)Ocean County Soil Conservation District (http://www.soildistrict.org/)

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“The previous methods to assess compaction can indicate whether or not compaction is present, but they can’t help you measure the extent of compaction. For that you need a measuring device known as a penetrometer, or soil compaction tester.

The penetrometer measures the resistance of the soil in a pressure gauge mounted at the top of a pole inserted into the soil. The pointed tip of the penetrometer is designed to mimic a plant’s roots as it grows through the soil Soil compaction is measured andmimic a plant s roots as it grows through the soil. Soil compaction is measured and reported as the depth reached when the pressure gauge reads a soil resistance of 300 psi.”


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“What I need from you after this workshop is to use a penetrometer at home to measure soil compaction and report the results back to me. I will now describe the procedure for taking soil compaction measurements properly with a penetrometer.”


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“To maintain consistency in sampling, I am asking that all of you sample only the grassed, turf areas of your yards. Since turfgrass is pretty constant over residential areas, it will allow for comparisons between different yard if samples come from the same types of vegetation.”


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“When you collect your samples, make sure that you do so 2‐3 days after it rains or after you irrigate your lawns. As mentioned previously, soil compaction is most likely when soil conditions are not too wet nor too dry. By waiting a few days after it rains or after you irrigate, it ensures that you’re collecting the measurements during this critical stage.

As you can see from this graph, when conditions are too dry compaction will usually be measured making this measurement a ‘false positive ’ Where conditions are too wet themeasured, making this measurement a false positive. Where conditions are too wet, the penetrometer will slide too easily through the muddy soil and give an overestimation of the looseness of the soil.”


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“The first step to taking a soil compaction measurement is to ensure that the equipment is working properly. First, inspect the dial at the top of the tester to make sure it is set at 0 psi and the dial is all the way over to the left.

Remove the locking ring by unscrewing the nuts from the ring with an adjustable wrench and sliding the ring off of the penetrometer. The wrench is provided in the set of field equipment that we will provide to you when you sign up to test your yards ”equipment that we will provide to you when you sign up to test your yards.

ADD IF APPROPRIATE: “Just a reminder that you have been given copies of the procedures today, and that a copy of the procedures will be with the field equipment you will get to take the soil compaction measurements.”


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“Next, screw on the smaller of the two cone‐shaped tips onto the end of the penetrometer rod. Then install the rubber o‐ring by slipping it over the conical tip of the penetrometer and making sure that it rests snugly on the lip of the cone tip.”


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“To take the compaction measurement, grab the penetrometer by the handles and insert the pointed end of the rod into the soil. As you push the device into the ground, apply even pressure to the handles on the instrument to keep the rod point penetrating the soil at a slow and even pace. Be sure to keep the instrument as vertical as possible and not to lean forward as you push the penetrometer into the ground.”


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“Push the penetrometer into a random location in your yard until the gauge reads 300 psi, then stop.

NOTE: The inner ring of the gauge is read when the ½‐inch tip is installed.”

Photo Credit(s):Steve Yergeau Rutgers Cooperative Extension of Ocean & Atlantic CountiesSteve Yergeau, Rutgers Cooperative Extension of Ocean & Atlantic Counties

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“Pull the penetrometer out of the ground slowly. Then, measure the distance that the rod has penetrated into the soil from the end of the ½ inch tip of the instrument to the point on the rod where the rubber o‐ring has stopped. This is your ‘depth to compaction.’ Record the depth (in inches) on the data sheet. Carefully wipe off the instrument with a rag or paper towel before taking additional measurements.”

Photo Credit(s):Photo Credit(s): Steve Yergeau, Rutgers Cooperative Extension of Ocean & Atlantic Counties

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“Before taking additional measurements, reset the rubber o‐ring by sliding it to the end of the rod where it meets the ½ inch conical tip.

Continue the steps to take a total of ten measurements at random locations in your yard. Make sure that all measurements are taken in turfgrass areas only.”


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“When you finish with the ten measurements, remove the penetrometer tip by unscrewing it off the rod and also remove the rubber o‐ring. Reattach the locking ring by sliding it all the way to the top of the rod and tightening the nuts with the adjustable wrench. You know the locking ring is securely in place when you can push the penetrometer into the ground and the needle does not move.”


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“Finally, take a composite soil sample, by gathering several small soil samples from random spots in your yard and combining them into the sampling bag. Take samples from just below the turf roots. You do not have to take these soil samples from the exact same spots as the compaction readings, just in the same section of yard and vicinity you measured.

Once completed, return all of equipment, the completed data sheet, and the soil sample bag with your sample to the office ”bag with your sample to the office.


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“Thank you for your time and I’ll take any questions you may have.”


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understanding soil compaction - ocean county · slide 2: “the outline for this presentation is as...

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