The sad state of soil is the common cause of failure in vegetable gardens, herb gardens, secret gardens, and even rain gardens. So whether you are a gardener, a professional landscaper, or a farmer, improving the soil is your number one priority in growing a healthy garden or maintaining an attractive landscape. The soil is the lifeblood of your plant’s health. Though not everyone is blessed with good soil, everyone can improve their soil fertility.
Soil augmentation, soil amendment, or soil conditioning are synonymous and mean the same thing. If your goal is to recover or improve the soil quality, structure, nutrients, and pH by adding organic and inorganic materials to make it fertile and conducive for growing plants, you’ve come to the right place. That is the true definition of soil augmentation. This article will teach you all you need to know to get your soil back into tip-top shape. We will use soil augmentation to describe this action throughout this article for commonality.
Before diving right in on what organic and inorganic materials we can use, let us first cover soil basics. By having a basic understanding of soil, we will know how to augment or treat our soil to bring it back closest to its ideal condition. But if you are already familiar with soil, feel free to skip this section and jump right into the soil augmentation topic.
In this article, we will talk about:
- What is ideal soil?
- Understanding the properties of soil
- Soil Augmentation: The secret to regaining your soil’s fertility
- Types of Soil Augmentation
- Soil Augmentation Application
Shall we dig in?
Table of Contents
What is an Ideal Soil?
The soil is the foundation of every successful sustainable garden, and it’s also the key to the most successful and breathtaking landscapes. Vegetables, perennials, shrubs, and trees grow best when the soil is fertile.
The soil supports and creates an environment for plants to grow by providing:
- water to carry nutrients to the plants
- air needed by the roots for respiration
- nutrients such as Nitrogen, phosphorus, potassium, sulfur, calcium, etc.
- microbes that feed on water, air, and nutrients and in-turn aid the roots in absorbing the nutrients
- serves as a base or anchor for the plants
For optimum plant growth, the soil should ideally contain 50% solids and the remaining half a combination of air and water. The solids contain 45% minerals: sand, silt, or clay or their combination, and 5% organic matter, which is residue from plants, animals, and other organisms.
The other half, consisting of 50% water and 50% air, creates the “pore space.” The pore space affects the plant’s ability to take up nutrients and grow its roots. For example, the pore space is compressed if the soil is compacted, limiting the roots’ movement, which affects their ability to get nutrients from the soil. Understanding the concept and their relationship will help us balance what contributes to healthy plant growth.
In reality, most of us don’t have this ideal soil mixture due to topography, climate, existing soil texture, and even soil management practices. Soil texture refers to the size of the particles that make up the soil and determines whether it is sandy, silty, clayish, or loamy. Soil management may refer to tilling practices that increase pore space or poor drainage, leading to soil compaction and reducing the pore space.
Understanding the properties of soil
Soil has several properties such as its physical makeup, chemical and biological content, color, etc. But our focus will only be on properties that influence plant growth. This will help us understand and appreciate the areas where we can intervene and help restore the soil’s fertility through soil augmentation methods.
This is the physical makeup and attributes of soil. The essential characteristics that contribute to plant growth can be classified under soil texture and soil structure. Soil texture influences its nutrient contents and ability to hold and drain water. Soil structure also affects the soil’s ability to hold and drain water, the movement of air and water, its ability to absorb nutrients, and how easy it is for the plant roots to grow.
As mentioned, soil texture pertains to the relative size of the particles that comprise the soil’s minerals, which also determines the soil type.
- Sand (2.0 to 0.05mm in size) – is porous (water and air can pass easily), cannot hold nutrients, is light, and feels gritty when rubbed between fingers.
- Silt (0.05 to .002mm in size) is more fertile than sand and clay, adds body to the soil, and feels smooth to the touch like flour.
- Clay (less than 0.002mm in size) – is heavy and retains nutrients and moisture (and does not drain well); it is sticky to the touch and can be molded.
- Loam – the combination of sand, silt, and clay that offsets their adverse effects. This is the type of soil every gardener would like to achieve because it is fertile, easy to work with, and has good drainage.
Soil structure describes the soil particles’ arrangement how they clump together and form aggregates. The aggregates are held together by organic matter such as decaying plants and animals. The arrangement of the soil particles creates spaces or pores in between. The pores’ size influences air and water movement in the soil structure. This movement is also called “aeration.”
A well-structured soil is friable or crumbly to the touch, and it is easy to work with. The well-structured soil is perfect for seedlings as it allows the tender roots to establish a robust rooting system. A well-structured soil can be achieved by the proper mixture of solids (sand, silt, and clay), good tilling practices, and soil augmentation.
A poorly structured soil is compact and tends to collect water. Because the pores are tight, it creates poor drainage and aeration. The result is soil that stunts or prevents plants from growing.
The soil’s chemical properties are essential to soil fertility and plant growth, and it influences the soil’s capacity to store and release nutrients such as Nitrogen, phosphorus, potassium, etc.
The soil’s pH level determines the soil’s chemical property, and the soil pH affects the availability of nutrients to the plant. The soil can be acidic (pH less than 7), neutral (pH of 7), or alkaline (pH more than 7). While most plants grow best in a neutral pH environment, certain plants still prefer an acidic or alkaline habitat. To know which plants grow at a particular pH level, you may download The pH Reference of Plants by the Hawaii Cooperative Extension Service of the University of Hawaii.
The soil’s pH level may change over time as minerals are leached away.
When this happens, the soil may become more acidic. Or because of conditions where the soil is often dry, high soluble salt content develops, making the soil alkali. In both cases, soil augmentation comes in to correct the pH imbalance.
The soil’s biological properties cover the microbes and other living organisms in the soil’s organic matter. The organisms break down the organic matter, the decaying plants, and animals and make the nutrients available for uptake by the plants. The soil organisms also store the nutrients in their bodies, preventing nutrient loss by leaching. Other organisms, such as the earthworm, help rework the soil through burrowing, ingestion, and defecation of sediment grains.
Soil Augmentation: The secret to regaining your soil’s fertility
Soil degrades and loses its fertility over time due to excessive rainfall that causes flooding or erosion, drought, improper use of pesticides or fertilizers, and unsustainable farming practices that deplete the soil nutrients or affect the soil structure. The soil’s pH may also change, which affects the type of plants that can grow in your landscape or garden.
This is where soil augmentation comes in. Adding organic and or inorganic material to the existing soil will improve soil properties such as:
- water holding capacity
- availability of nutrients and
- living conditions of soil organisms
All these contribute to plant growth. Almost all types of soil can be made fertile using this method. The amendment factors can be applied to the soil locally and by anyone who can handle a shovel.
Types of Soil Augmentation
Soil augmentation can either be organic or inorganic matter. Sometimes it can be a combination of both.
An organic matter comes from something living, such as a decaying plant, animal, or organism. This can be humus, compost, mulch, aged manure, biosolids, peat, wood chips, hardwood bark, sawdust, shavings, and wood ash.
Inorganic matter is mined or man-made. This includes sand, profile soil conditioner, peat gravel, lime, sulfur, vermiculite, and perlite.
Organic matter is the most effective and practical remedy for improving soil conditions. A small part of organic matter can significantly impact the soil’s physical, chemical, and biological properties. It provides aeration, better drainage, holds water well, and can keep nutrients. It addresses a lot of soil issues.
Humus is the black, spongy, and jelly-like carbon matter that remains after dead plants and animals have decayed and microorganisms have completed processing and breaking down the organic matter to its final state. This process takes a considerable amount of time or years to complete. Humus has many mineral nutrients that aid in soil health and fertility. Since hummus is rich in carbon, this makes it ordinarily acidic.
Benefits of hummus:
- it retains the nutrients in the soil like Nitrogen, phosphorus, calcium, etc.
- improves moisture retention making it more drought resistant
- traps oxygen needed for respiration by the roots and microorganisms
- feeds and protects microbes
- prevents erosion by helping bind the soil particles
- helps root structure by improving soil porosity
- stabilizes temperature and
- corrects soil PH.
Also called “black gold,” compost is decomposing organic materials recycled from kitchen waste or plant scraps, dried leaves, branches until it is crumbly and looks and smells like soil and not rotted vegetables. Compost adds nutrients and aids in microbes’ activity to release more nutrients to the soil, and compost can balance the soil’s pH level.
Benefits of compost:
- retains moisture
- encourages microbial growth that produces humus
- suppresses plant disease and pests with the help of beneficial microorganisms
- Reduces the need for fertilizers
Dried leaves or cuttings, shavings, or any organic material placed as a layer or covering on top of the soil. Realize that when applying fresh cuttings, they will compete with the plants in taking up the Nitrogen in the soil as the cuttings decay. To address this, supplement the soil with Nitrogen. Most mulches tend to raise the pH level of the soil slightly.
Benefits of mulch:
- improves soil moisture by reducing evaporation and water run-off
- regulates soil temperature
- reduces soil erosion and compaction
- helps in soil nutrition as it decomposes
- acts as a weed control
Aged Manure and Biosolids
Aged manure is animal dung from cows, horses, goats, sheep, chickens, and even bats composted for 4-6 months. Aged manure is a good source of Nitrogen, Phosphorus, and Potassium, and it is also sometimes mixed with the compost. Animal manure tends to raise soil pH because it contains calcium and magnesium.
Fresh manure is not advisable as it contains high uric acid levels, which may burn the roots. It may also have pathogens that may contaminate the plant and make it harmful for human consumption, especially when eaten raw.
Biosolids are sludge recovered from sewage treatment plants that have been physically and chemically treated. Biosolids are often high in salts and may have the potential for heavy metals, and it is not advisable for use in the vegetable garden. Biosolids also have a high chance of raising the soil’s pH level, especially with those treated with lime at the processing stage to stabilize the organic matter and reduce pathogens.
Benefits of manure and biosolids:
- adds nutrients such as Nitrogen, phosphorus, potassium, and other micro-nutrients
- conditions the soil by loosening compacted soil
- reduces run-off or leaching of nitrates
Peat is known as “turf,” which are brown deposits of partially decomposed organic materials formed in wet, acidic conditions of bogs, peatlands, mires, moors, or muskegs. It is acidic (low pH level) and ideal for acid-loving plants like blueberries. It is an excellent amendment for sandy soil because of its water-retention property.
Benefits of peat:
- helps in nutrient retention
- increase in water retention makes it ideal for sandy or rocky soil; also stabilizes clay soil
- provides good aeration
Wood Chips, Hardwood Bark, and Shavings
Wood chips and shavings are the small excess pieces or waste materials resulting from cutting or chipping trees, branches, lumbers, or other wood materials. Hardwood barks are the outer covering of hardwood trees discarded when cutting tree logs to make lumber.
Wood chips, hardwood barks, and shavings are applied as layers over the soil top like mulch. But they are denser and take longer to compact and break down. Note that wood chips, hardwood bark, and shavings need Nitrogen to decompose. Because it is competing with the plant in using up this nutrient, this may result in nitrogen deficiency to the plant. To avoid this, a nitrogen supplement may be required. Like mulch, it tends to raise the pH level of the soil. But using pine bark may cause it to be more acidic.
Benefits of wood chips, hardwood bark, shavings:
- improves soil moisture
- regulates soil temperature
- reduces soil erosion and compaction
- helps in soil nutrition
- acts as a weed control
Because inorganic matter is extracted or processed, they are not as sustainable and more expensive than organic augmentation. They also need large volumes to make significant changes to the soil’s physical properties. Inorganic matter is used to increase aeration and drainage, decreasing the water-holding capacity.
Sand, Profile Soil Conditioner or Pea Gravel
Sand is a granular mineral particle in size, profile soil conditioner is a ceramic-type particle that is porous, and pea gravel is a smooth small rounded stone the size of a “pea” vegetable.
Benefits of sand, profile soil conditioner, or pea gravel:
- improves water and nutrient holding capabilities at the root zone
- improves aeration
- reduces compaction
There are two types of lime used for soil augmentation, agricultural lime and dolomite lime. Both limes contain calcium, with dolomite lime having extra magnesium. Lime is generally used to correct the pH of acidic soil.
Benefits of lime:
- improves pH of soil by making them less acidic
- aggregates soil particles and improves aeration
A mineral that, when in contact with soil bacteria, changes to sulfuric acid and lowers the pH of the soil—used to either bring soil with an alkaline pH to neutral levels or make a neutral pH soil become acidic.
Benefits of sulfur:
- makes the soil more acidic
- reduces the sodium content of the soil
A mineral that resembles mica in appearance that is dark brown to golden brown in color. When heated, it forms flakes with a pH of 7.0 and can soak up 3-4 times its volume in water, making it ideal for water-loving plants. It is generally used with potting-mix soil.
Benefits of vermiculite:
- Improves aeration
- aids in water retention
- increase oxygen levels at the root zone
- reduce compaction
- ease drainage when soil is saturated
Perlite is an amorphous volcanic rock which when heated, expands like popcorn. It is whitish in color with micro air bubbles making it light and able to keep moisture. It has a pH of 6.6 to 7.5. Best for indoor cactus plants. It cannot be used with garden soil since it will be crushed. Best used with a potting mix like peat moss.
Benefits of perlite:
- improves aeration and drainage
- keeps the soil loose
- prevents compaction
Soil Augmentation Application
It is not realistic to change the texture of the soil. A large volume of a soil type (sand, silt, or clay) will be needed to achieve an ideal soil condition. Focus instead on improving the soil structure. Do this by addressing the organic content, which will impact the soil’s porosity. Soil porosity is ideal at half pore space and half solids, with the pore space being filled by half air and half water. This change will also influence the nutrient uptake and microorganisms living in the soil.
Of the organic matter mentioned, humus, compost, aged manure, and biosolids are often used to condition the soil and bring it to its fertile state and neutralize the pH. Do not use peat, sand, vermiculite, or perlite. Peat makes the soil acidic; sand will harden the soil like concrete, and vermiculite and perlite are expensive. Most inorganic matters are generally used in potting mixes or seedling beds.
When doing soil augmentation, work on the top 6 to 8 inches deep of your soil. Place 2 to 3 inches of organic matter or 1 inch if it’s manure or biosolids and thoroughly mix into the soil to distribute evenly. Simply dumping or burying it in the soil will not work, and it may interfere with air and water movement and root growth. It has to mix with the existing soil to allow the organic matter to clump and achieve aggregation. If mulches, wood chips, hardwood bark, and shavings will be used as an organic matter mix, it must be composted first. Otherwise, it is suitable for surface application only.
Because organic matter such as compost, humus, and manure breakdown easily, it is best to apply and till the organic matter yearly at the start of the planting season. This ensures that your soil maintains its fertility throughout the season.
To get a clear picture of your soil’s health, you may conduct your test based on the Soil Testing Methods Manual by FAO. Or, for a more thorough analysis of your soil pH and nutrients, you may take a soil sample and send it to the nearest soil testing lab.
The pH level can be corrected using lime or sulfur following the procedure used when applying the organic matter. Note that it may take six months for the lime to react to the soil. The best time to apply lime is during fall. For nutrients lacking in the soil, this can be supplemented by applying the corresponding fertilizer. It is recommended to do a soil test at least once every 2 to 3 years.
With these recommendations and incorporating soil augmentation into your workflow, you can provide a healthy environment for your vegetables, perennials, shrubs, and trees to grow. This also raises your chances of success in any garden or landscaping project you plan to undertake.