Heal Compacted Soil

 

“Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past.” —  Kellogg

Parts adapted from http://www.ediblelandscapingmadeeasy.com/tag/roots/

Compaction makes it difficult for water to penetrate, for air to infiltrate and for roots to grow in a healthy manner.

Soil Compaction TheOrangeGardener_Org

Compaction results when soil particles are pressed together, reducing pore space and aeration.  The damage to the soil structure reduces the soil’s ability to hold and conduct water, nutrients, and oxygen.  Rate of water infiltration is decreased and more water is lost to runoff.  Other effects of compaction include decreased organic matter, reduced microbial activity, poor drainage, increased erosion, and nutrient leaching.

These undesirable effects on the soil directly affect plant growth.  Roots have increased difficulty when penetrating the soil which often results in reduced root growth and reduced ability to take up water and nutrients.  Compacted soils can cause short and stunted plants.  Severely compacted areas often have sparse growth or are bare due to these problems.

To stop and heal compaction:

A. Observe to define the source of compaction. Brainstorm ideas to naturally re-route compacting traffic and to define official paths. For example, line the trail with curved branches (i.e. not flat), install a log, etc. Or if a stronger sense of border is needed to hold the area or to regain area, construct a short ‘fence’:  Drive 3′ segments of thick stemmed branches {or try live stakes} into the ground alternating a few inches apart in 2 rows. Along these branch posts intertwine long narrow branches, vines, & leaves between rows. {If you place sticks on soil level, you can intertwine ivy above to dry out.}

B. Turn the soil, flatten, and add several inches of an organic mulch to hold in moisture, decompose and serve as a food for small animals and beneficial microorganisms. Mulch material depends on site circumstances. The first choice in mulch is a mix  of native materials from the area that mimics natural processes {e.g. native plant leaves, pine needles, cones, branches, etc.}, but since there is generally a shortage of this material in our urban forest and it’s also best to not disturb this material, another option is to use nonnative material {e.g. blackberry canes (leaving roots & tips high & dry), laurel branches, etc.}. Arborist mulch {which includes leaves, needles & cones} is preferred over woodchips. Another option is combinations of site material and hauled in mulch, for example woodchips with thorny blackberry stems on top to prevent further compaction .  Over time the mulch will be worked into the soil by small soil creatures and improve the soil.

C. For large bare areas where there is less control over the source of compaction, the priority is to prevent further compaction. After that is achieved, work slowly from the least compaction toward the most. Apply mulch in narrow strips (3′ – 4′) along inner compacted area borders with a means to prevent traffic on top of mulch. After a season with mulch, plant patches of barrier species that belong in the plant community. Then mulch another adjacent narrow strip of the bare area.

D. Plant site appropriate species with strong, deep roots, or seed in first successional species to hold the space and naturally amend the soil until second successional species move in.  First successional plant roots not only break up the soil, but decompose when they die adding organic matter  and minerals such as nitrogen to the soil.

The right plant can:

  • Increase the  organic matter content of the soil
  • Increase the availability of nutrients
  • Improve the soil’s tilth {soil texture}
  • Reduce weeds by choking out undesirable plants
  • Reduce soil pests
  • Enhance soil’s biological activity.

Compaction & soil type: Different soil types react differently to being walked on.

Sandy soil has the largest particles among the different soil types. It’s dry and gritty to the touch, and because the particles have huge spaces between them, it can’t hold on to water and does not compact so easily.

Silty soil has much smaller particles than sandy soil so it’s smooth to the touch. When moistened, it’s soapy slick. When you roll it between your fingers, dirt is left on your skin. It can easily compact and become poorly aerated.

Clay soil has the smallest particles and has good water storage qualities. It’s sticky to the touch when wet, but smooth when dry. Due to the tiny size of its particles and its tendency to settle together, little air passes through its spaces. This type of soil is also prone to major compaction.

 

Segments of training from Rodney Pond – PhD Student in Restoration Ecology UW

Excited Skin of the Earth

Soil is:

*A growth medium for plants – provides physical support, water, nutrients, reproductive environment. Ideally 1/2 pores for 1/ water, 1/2 air for effective evapotranspiration..

*A complex ecosystem – 1. soil biota, 2. soil structure, 3. plant-soil interaction, 4. system complexity: organic matter (waste, residue and metabolites from plants, animals and microbes)), plants roots, nematodes, fungi, bacteria, arthropods, nematodes, protozoa, arthropods, birds feeding, animals feeding, tunneling, etc.

*The excited skin of the Earth!

Soil Layers:

O – Organic layer (leaf, humus, plant residues, organisms decomposed organic fibers)

A – Topsoil (mineral particles, organic matter, rich humus)

E – Thin leached layer (low organics , fine particles being washed downward}

B – Accumulation zone – collection of leached materials. Clay + calcite + gypsum.

C – Parent material – Little changed by soil formation, but generally partially weathered.

R – Bedrock – Unweathered parent material.

Soil texture is determined by ratio of  particles

*Sand .05 – 2mm, feels gritty

*Silt .002 – .05,  feels smoother

*Clay <.002, feels smooth & sticky, chemically transformed, electrical charge

Soil structure – granular (like crumbly garden soil) & blocky are preferred & most common in our area. Sandy & compacted structure are the most challenging.

Soil Disturbances – compaction (less O2, infiltration, root penetration, biota), erosion (loss of organic topsoil, lack of biotic activity, altered hydrology), clear cutting (rapid changes in coil tem, initial loss of nutrients, drier), invasive species (altered nutrient cycling, altered hydrology, sediment accumulation, altered fire regime), fire (soil heating, death of biota, loss of nutrients, root kill, loss of organic matter, decreased infiltration), pollution (decreased biotic activity due to toxicity, slowed nutrient cycling, water repellency)

Soil Management for Restoration

Assessment – soil pits (soil horizons, moisture, texture, root zone, surface structure, plant community, critters), CLORPT (climate, organisms, relief, parent material, time), disturbances (erosion, compaction, flooding, sedimentation, contamination, invasive plants), site characteristics inventory for each vegetation zone.

Conservation – {INTACT SOILS CONTAIN LIVE CULTURES!} preserve intact natural soils: restrict access, erosion control, temporary covering, stockpiling.

Topographic alterations – recontouring, constructed features, hydrology to support plant community.

Amendments – Replace what’s missing: organic matter, inoculants, inorganic matter, cover crops.

Surface treatments – protection (erosion control, moisture retention, temperature moderation), soil ecology (seed germination, soil biota, habitat, nutrients, organic matter), forms (organic mulches, inorganic mulches, woody debris, stone).

Soils & Invasive Control – removal techniques (topsoil removal, burning, herbicide, cutting, manual removal, suffocation), barriers to re-establishment (thick mulch, low nutrient conditions, conservative watering)

Effects of Preparation on Soil Development – increasedmoisture, organic matter, biotic activity, available nitrogen; decreased bulk density, water loss, temperature fluctuation, erosion.

 

Segments of training from Nicole Jacobsen

Soil Ecosystem – All soil is made up of air, water, living and/or dead organisms (organic matter), and mineral matter (sand, silt, clay). The relative proportions of these four major components greatly influence the behavior and productivity of soils. Although mixed in complex patterns, the proportions are relatively consistent. A handful of soil may seem to be solid, but about half the soil volume actually consists of pore spaces filled with air or water.

Energy Cycles and Food Webs – The energy cycle begins when the sun’s energy is captured by the plant-based food web. Energy flows from the sun, through plants, and through many trophic levels of soil organisms. This energy is recycled repeatedly through soil organisms. Nutrient availability is governed by the detritus-based (below ground) food web.

Soil organisms can be divided into six groups: bacteria, fungi, protozoa, nematodes, arthropods, and earthworms. Within each group, here is great diversity of form and function and each group plays important roles. Macro- and micro- environmental characteristics largely determine the structure of soil communities, particularly the species present and their level of activity. Conditions such as temperature, moisture, aeration, pH, pore size, and types of food sources are especially influential.

Soil Functions – Soils play a very important role in storing, regulating, and filtering both air and water resources. Concurrent soil functions include: soak up rainwater and limit runoff impacting groundwater recharge and flood-control, store and release water, air and nutrients for plants and animals to use, store carbon and prevent its loss to the atmosphere, filter water and air, buffer, degrade, immobilize, detoxify, and trap pollutants and keep them from entering groundwater.

Soil organisms – Bacteria, fungi, and other micro-organisms are largely responsible for breaking down dead plants and animals in soil. Small organisms (microbes) have negatively charged sites where soil nutrients can bind to form soil aggregates and compounds. Earthworms and larger animals eat and digest organic materials and minerals, transform them into soil aggregates, and deposit them as waste.

Soil organisms are part of a living system. In most ecosystems, there is more life and diversity underground than above. A single square meter of forest soil may support 250,000 arthropods, ranging in size from the microscopic mite to the highly visible, orange-striped shiny black millipede. Millipedes eat between 1/3 and 1/2 of the foliage that falls to the forest floor. Arthropods are numerous in undisturbed forest soils. Earthworms are common in deciduous forests, but rare among conifers.

Forest soils have high ratios of fungi relative to bacteria; coniferous forests may have 100 to 1000 times more fungal biomass than bacterial biomass. The fungi are mostly ectomycorrhizae that infect tree roots and then extend their hyphae into the soil. A single gram of soil may have many kilometers of mycorrhizal hyphae and tens to hundreds of millions of bacteria representing more than 10,000 species This greatly increases the tree’s effective root zone, allowing access to a greater area of soil from which to extract water and nutrients. The mantle (dense sheath) created by mycorrhizae around the root also helps prevent pathogenic fungi and bacteria from attacking the root system.

The rhizosphere is the interface between plant roots and the soil environment. It is the location of much soil biological activity and plant-microbe interactions including symbioses, pathogenic infection, and completion. As much as 50% of a tree’s photosynthesis may be used to support its fine roots and the fungi and bacteria in the surrounding 2-3 mm-thick rhizosphere.

Plant growth and nutrition are closely linked to soil properties; organic matter is the heart of a forest soil. The ability of soil particles to hold and release nutrients for plants and micro-organisms to use is called cation-exchange capacity (CEC). Organic matter has many active sites that bind chemicals (high CEC) in a manner similar to the way clay particles bind chemicals in soil (almost as high a CEC as organic matter). Clays and other soil materials are mixed with organic matter in each soil layer to form a chemical system. In general, CEC is directly linked to soil fertility.

Biological Processes in Soil – Biological processes in soil proceed simultaneously and in complex interrelationship: nitrogen fixation and transformation, nutrient capture and cycling, carbon cycling, water and oxygen exchange. Good soil management practices generally favor desirable biological activity. For example, minimizing soil compaction maintains not only beneficial soil physical properties but also optimal populations of soil organisms.

Organic Matter  – A large portion of the nutrient capital in the forest ecosystem is contained in the forest floor. Organic matter is often visible in a thick, dark surface layer in which plants begin to grow and take up nutrients. Organic matter is the main energy source for micro- and macro- organisms in the soil. Activities of these organisms play an important role int he maintenance of soil fertility, particularly in the development of optimal soil physical conditions. A number of factors determine the rate of decomposition and humus formation, but perhaps the most important are temperature, moisture, and chemical content of the litter, particularly N content.

Disturbed Soils – There is no such thing as an imappropriate soil, but not all soil types are suitable for many uses that humans desire. In many ways, disturbed soils differ form soils in natural areas: horizons may have been mixed, destroyed, or removed; structure has likely been altered or destroyed; compaction has likely occurred; water transmission rates have probably been reduced; runoff and soil erosion rates typically have increased.

Urban soils that have been disturbed and mixed may no longer posses the natural characteristics needed to support life. Soil amendments, modifications and other interventions may be required to re-establish plants.

After soils are disturbed, the landscape must still function as a natural system. In other words, the soil must still regulate, partition, and filter air and water; sustain biological diversity and productivity; and support structures. Effective management includes overcoming the physical and chemical root restrictions, providing nutrients by managing fertility and acidity, and reducing the likelihood of contamination or disease problems.

Compaction – For practical purposes, compaction is permanent. This is especially true of deep compaction. Unintentional compaction is a symptom of mismanagement and can be a cause of excessive runoff.

Even a single compaction event can significantly affect the location and quantity of the food supply and the physical habitat of soil organisms. If enough nitrogen is present, practices that mix the soil usually lead to a flush of microbial activity and nutrient release, and loss of soil organic matter via CO2 respiration.

Soil composition can be dramatically changed by pedestrian traffic, especially when the soil is wet. The soil components most easily changed by compaction are the amounts of soil air and water. Trees are especially sensitive to compaction and low soil oxygen levels.

Soil has structure and porosity and a complex biological community that develops over long periods of times. Soil structure is important to hydrologic function of a soil: soil biology is important to nutrient cycling.

The size and continuity of pores controls whether larger microbes, such as protozoa, can prey upon bacteria and fungi. Compaction reduces the diversity of pore sizes and the amount of space and pathways available for larger organisms to move through the soil. This favors bacteria and small predators over fungi and the larger predators. Arthropods are severely affected by compactions.

Take-home message: where healthy soil and trees are present, it is more effective to preserve existing soil than attempt to remediate the damage caused by compaction.

Erosion – Most soil organisms – especially the larger ones – live in the top fes inches of soil. Erosion disrupts and removes the surface habitat while sedimentation buries the surface habitat and deprives organisms of space and air.

Unmanaged use of parks can cause damage to plants and severe soil compaction, which restricts the movement of water into the soil. The result is increased soil erosion, poor plant vigor and growth, increased runoff and offsite sedimentation, and restoration costs.

Invasive Plants – Invasive plants can cause a shift in the types of soil organisms present because the quantity and quality of plant residue and root exudates change. Plants that cause increased litter buildup tend to promote more fungal dominance in soil. The encroachment of annuals into perennial plant systems will cause changes in organism community composition because soil biological activity corresponds with plant growth stages and periods of litter fall and root die-off.

Qucik Soil Health Assessment:

Get to Know Your Community

Thorough soil health assessments require background investigation and monitoring of parameters over time. Relevant background information and monitoring areas may include historic and current regional and local land use (local knowledge, Dept of Ecology’s Dirt Alert Program, site management plans), current vegetation and changes over time (plant health, status of invasives, persistently bare or muddy areas?), wildlife use, diversity and abundance (historic vs. current use, types and diversity of species, pollinator-friendly plants?).

Soil Organisms

Choose a few places to closely examine your soil ecosystem. Look under a shrub, in the woods, along a fence line, in a field, etc. Examine the plant litter and look for organisms that move. Look for biotic crusts, burrows, fungal hyphae, and other evidence of soil organisms. Over the seasons, look for birds and bats feeding on insects. Observe the rate that leaves and annual plants decompose. Notice the amount of runoff or ponding after a rain.

ChemicalProperties

The soil solution is the immediate source of most nutrients used by plants. The chemistry of the soil solution includes many different elements and inorganic compounds, as well as organic compounds and gasses. The composition and dynamics of the soil solution depend on interactions  with the solid phases of the soil, as well as on the overall ecosystem biogeochemistry.

Physical Properties

Get dirty! Dig a hole and pull out a soil aggregate – texture, particle size, structure, and consistency can all be determined in the field by touch and feel. Color can be generalized. Bulk density can be ‘guesstimated’.

Texture and Particle Size

Fine-textured soils have higher available water storage capacity, tend to retain more water, are usually more poorly drained, and often have low load-bearing capacity compared to coarse-textured soils that have higher/faster water flow. Trafficability is best on coarse-textured soils (e.g. very gravelly loamy sand).

Structure and Consistency

Massive, or structureless, soils are prone to puddling. Soils with large water-stable aggregates are less prone to erosion. Uncompacted, friable soils with large, stable aggregates generally have good soil aeration. The ideal consistency for plant growth is ‘friable’ when moist (i.e. the soil mass coheres when pressed together, but crushes under gently to moderate pressure between thumb and forefinger).

Color

High chroma and red to yellow-red hues suggest abundant free iron oxides. Low chroma and bluish hues indicate poorly drained areas. Low values are usually associated with high organic matter content.

Density

Glacial till and surface horizons compacted by traffic will likely have high bulk density.  Organic forest soils may have a bulk density of .13 g/cm3; whereas surface mineral horizon might be near 1.0 g/cm3. Root penetration is impaired above 1.2 g/cm3 and complete at 1.8 g/cm3.

 

 

Any ideas on how to coax in and protect moss?

Email suggestions & stories to mekwamooks@yahoo.com.

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