Soil Amendments: Why and How to Use Them

Soil amendments are any supplements applied to the soil to improve its condition in terms of its physical and biochemical functions.

They are also called soil conditioners, and they are nutrient-rich.

Productive soil is the foundation for every gardener, but very few gardeners know how to convert their garden soil into a productive one.

Healthy soils are ideal for plants as they contain all the essential nutrients required for growing plants.

Soil amendments can be animal or green manures, cover crops, decomposed materials, organic wastes, bio-solids, etc. [1].

However, scientists often recommend not using industrial waste to amend the soil for organic gardening as those by-products may contain heavy metals or other harmful chemicals.


If you’re looking for other types of soil or fertilizers to use in your garden, go back to our Soils and Fertilizers page.


Why should you use soil amendments?

Soil conditioners will improve the soil texture and condition by ensuring better aeration and water holding capacity.

Compost or composted materials, peat moss, coco peat, worm casting, leaf mold, or plant debris encourage microbial activity.

After decomposing, the released organic compounds react with soil minerals and form organo-mineral complexes that ensure structural stability and water retention capacity.

Soil amendments or soil organic matter will increase plant growth by supplying essential macro and micronutrients [2].

Lettuces growing on soil amendments

Organic amendments produce organic acids after being decomposed by the soil microbes, and the acids retain large quantities of nutrients and minimize their runoff or leaching loss.

In addition, during the rainy season, you will not have to worry about soil erosion as the conditioners will protect the soil aggregates from the impacts of raindrops.

Although chemical fertilizers are concentrated in nutrients, they can lead to soil degradation by changing the pH abruptly and damaging the soil structure and microbial population.

Even these fertilizers can burn the plant roots if applied too close to the plants’ roots.

Without this, the nutrients released from the synthetic fertilizers are susceptible to leaching or runoff loss, which impairs the water quality.

Types of Soil Amendments

Soil amendments come in many different forms, each with their own benefits.

There are two significant types of soil amendments. Soil amendments are either contain organic matter or inorganic matter.

Below are some common soil amendments that are added to the soil for gardening.

Organic Soil Amendments

Organic-Soil-Amendments

Organic soil amendment is the process of adding organic matter to soils to improve their composition and function.

Organic matter refers to plant and animal material that has been degraded by aerobic or anaerobic processes but retains carbon, nitrogen, and other essential elements.

These amendments can be made in a variety of ways, including adding composted manure, aged chicken litter, and blood meal (dried animal blood).

Organic soil amendments include decomposable organic materials. These amendments are rich in organic carbon as well as macro-and micronutrients.

The benefits of using organic soil amendments are numerous. First and foremost, organic matter provides important nutrients for plants.

These nutrients include nitrogen, phosphorus, potassium, magnesium, sulfur, and iron.

In addition to providing these essential elements for plant growth and development, organic matter also helps amend the pH balance of soils, which can promote better root growth and nutrient uptake.

Alfalfa meal

Alfalfa meal is a by-product of the alfalfa crop that is composed of two main components: organic carbon and macronutrients.

Organic carbon is a key component in soil amendment because it helps to improve soil fertility, provide nutrients, and neutralize toxins.

Macronutrients are essential for plant growth and include nitrogen, potassium, and phosphorus. Alfalfa meal also contains micronutrients such as magnesium, zinc, and chromium, which are essential for plant health.

It is a popular organic amendment due to the balanced N-P-K (nitrogen-phosphorus-potassium) ratio.

If your soil lacks nitrogen, applying alfalfa will be one of the best choices as it is rich in nitrogen.

Blood meal

Blood meal is a by-product of the slaughtering process and consists of organic carbon, macronutrients, and micronutrients.

A blood meal is another type of amendment widely used by organic gardeners.

It is an important soil amendment because it increases the amount of organic matter in the soil and makes it more fertile.

Bloodmeal also helps to improve the growth of crops by providing them with essential nutrients.

This material is very high in nitrogen; the N-P-K ratio of blood meal is approximately 31-1-0.

Besides these significant nutrients, this organic fertilizer also contains a few trace elements at a minor concentration that are extremely important for the plants.

Chicken manure

Chicken-Manure-Soil-Amendments

Chicken manure is a by-product of chicken farming.

It is a dark black material composed mostly of nitrogen, phosphorus, potassium, and other nutrients that are essential for plant growth and organic matter.

It is an excellent soil amendment because it helps to improve soil fertility and increase crop production. As a bonus, chicken manure has a lot of organic carbon, which is good for the environment.

Chicken manure doesn’t contain nitrogen as high as blood meal, but it has a balanced nutrient content with the N-P-K ratio of 3-2-2.

It indicates that chicken manure contains 3% nitrogen, 2% phosphorus, and 2% potassium.

You may either use it in composted manure form or apply it directly, but we suggest you make compost from the chicken manure to increase its efficacy.

Coconut Coir (Coco Coir)

Coco-Peat-Soil-Amendments

Coconut coir, also known as coco coir and coco peat, is a natural soil amendment that is made from the husks of coconuts.

It is an organic carbon source and has high levels of nutrients, including nitrogen, phosphorus, potassium, and magnesium.

Coconut coir is highly eco-friendly and a solid alternative to peat moss in potting soils; it also helps to improve water retention and drainage.

Coco peat is mainly used to improve the potting mix’s drainage system and moisture retention capacity.

The downside of using coco coir is that it contains very few nutrients that feed plants.

Therefore, we suggest you use additional amendments with coconut coir. It is a good idea to mix coco coir with sand.

Compost

Compost-Soil-Amendments

Compost is made up of organic matter that has been broken down by microorganisms.

Compost also helps to increase the available organic carbon and nutrients in the soil, while improving the soil’s ability to retain water.

As an added benefit, compost also helps to improve the overall environment in your garden, reducing landfill waste.

It is one of the best organic fertilizers applied to any soil type.

It does improve not only physical properties but also encourages the activity of microorganisms in the soil.

Compost can be made of many materials, including dead leaves, branches, animal manure, and kitchen waste.

Compost amended soils are rich in essential nutrients and organic content, and they retain water for a longer period of time.

Kelp meal

Kelp meal is a type of organic matter that can be used in gardens to improve soil fertility and help with the growth of plants.

Kelp is a type of seaweed that grows in shallow waters and can be harvested from the ocean or lakes.

The seaweed is washed and dried before being ground into a powder. 

Kelp meal is a valuable and sustainable soil amendment that contains high levels of organic matter, which helps to improve the growth of plants.

Kelp meal also contains organic matter, which helps improve the soil’s texture and provides food for beneficial microorganisms.

Kelp meal is a high-quality source of macronutrients, including nitrogen, phosphorus, and potassium.

Kelp meal can be used as a fertilizer for plant growth and contains essential nutrients such as nitrogen, phosphorus, potassium, magnesium, and calcium.

The N-P-K ratio of kelp meal is around 1-0-4. Though the concentration of NPK is lower in this fertilizer, the level of plant growth hormone is very high.

So, it would be best to use kelp along with other organic fertilizers.

Peat moss

Peat-Moss-Soil-Amendments

Peat moss is a natural soil amendment that comes from the decomposition of bog plants.

It is another inert material like coconut coir. These materials absorb a lot of water and have a higher capacity for holding water than coco coir, but they are acidic.

It is a type of organic matter and is composed of plant cells and other organic materials.

Peat moss can improve aeration and drainage in soils, providing key nutrients to plants. It is also an excellent source of organic matter, making it an important part of a garden’s nutrient cycle.

The downside of peat moss is the harvesting of the material.

Harvesting peat moss is not considered environmentally friendly because once harvested, peat moss can take hundreds of years to form or regrow.

Worm castings

Worm Castings Soil Amendments

Worm castings are a type of fertilizer made from the castings (feces) of worms.

It is high in nitrogen and potassium, two of the key macronutrients that plants need in order to grow.

Worm castings also contain organic matter, which helps to improve soil fertility.

Worm casting is considered a complete fertilizer package and the best soil amendment because it contains all the macro and micronutrients.

It increases the organic content of the soil and improves the soil’s capacity to retain more moisture. You can mix it with the topsoil to improve the aeration.

Worm casting will minimize the abrupt fluctuation of soil pH and improve soil structure by flocculating the soil particles. 

Inorganic soil amendments

Inorganic-Soil-Amendments

Inorganic soil amendments include materials that are low in carbon. Some inorganic materials include gypsum, fly ash, vermiculite, and perlite.

Inorganic soil amendment refers to the use of substances that are not part of the natural soil composition in order to improve the quality or fertility of soils.

Common inorganic soil amendments include nutrients, gypsum, fly ash, and vermiculite.

Nutrients are essential for plant growth and can be supplied by adding them to the soil as a fertigation agent or as a component of organic fertilizers.

Perlite

Perlite is an inorganic material that is made of tiny pieces of volcanic glass and can be used as a source of potassium, magnesium, and other nutrients for plants.

Used as a soil amendment, perlite can improve the texture and structure of soil while reducing water uptake.

Perlite is a material mainly used for improving drainage conditions and maintaining soil pH.

Vermiculite

Vermiculite is a mineral-based insulation material that can be used as an amendment to soil because it provides good water retention and stability.

Vermiculite is a type of soil amendment that is composed of small, void-like spaces that are filled with a mixture of broken pieces of rock and other inorganic matter.

Vermiculite is a natural product that has been used in agriculture and gardening for many years and is most commonly used as a soil amendment because it increases the available space for plants to grow and allows them to better absorb nutrients.

It is extracted from the ground, exfoliated, and subjected to intense heat and pressure in order to expand; the result is a curly, worm-like appearance.

Vermiculite also helps to improve the texture and structure of soils, making them more resistant to erosion.

Ultimately, it helps the soil retain water and nutrients.

Fly Ash

Fly ash is a byproduct of the burning of coal and other fossil fuels. It is composed mostly of mineral components such as potassium, phosphorous, and sulfur.

Fly ash is used as an amendment to soil because it is high in nitrogen and phosphorous.

It can also be used as a fertilizer for plants because it has micronutrients, like zinc and magnesium, which help plants grow.

Gypsum

Gypsum is an inorganic mineral that is often used as a soil amendment. Gypsum can be found in nature as well as being produced industrially.

Gypsum has a high concentration of calcium and magnesium, which makes it an excellent macronutrient for plants.

Gypsum also helps to improve the moisture-holding capacity of the soil.

Lastly, gypsum can be used to control the pH level in the soil.

Dolomite Lime

Dolomite lime is a soil amendment that can be used in gardens to improve the quality and fertility of the soil.

Dolomite lime is made from dolomitic limestone, while gypsum is a type of mineral containing calcium sulfate that is found mostly in sedimentary rocks. 

Dolomite lime (agricultural limestone) can be used to fix nitrogen in the soil, which is important for plants because it helps them uptake nutrients.

Both gypsum and dolomite lime is used to control the soil pH.

If the soil in your lawn is too acidic, you can use any one of these to increase the pH value before planting any vegetables or other plants.

It contains around 23% calcium and 17%–18% sulfur. Instead of applying it to the topsoil, you should mix these materials within the first 7 inches of soil correctly.

FAQ

What is a soil amendment?

A soil amendment is a material that is added to the soil to improve fertility and helps increase plant growth. There are two main types of soil amendments, organic and inorganic matter. Organic matter includes materials such as manure, compost, coconut coir, peat moss, kelp meal, and worm castings. Inorganic matter, such as perlite, vermiculite, sand, clay, or limestone, helps bind the soil together and provides essential nutrients. Nutrients include nitrogen, phosphorus, potassium, and calcium.

When should I use soil amendments?

The best time to add soil amendments, organic or inorganic materials, is when you’re first starting out planting your garden. If you already have a garden, soil amendments are usually a year-round job, and they can be as simple as adding perlite, compost, or worm castings to the soil. However, if your plants are doing well, you won’t have to do much with the soil.

Do soil amendments work?

Yes, soil amendments work well. When used properly, soil amendments change the soil’s properties, making it easier for plants to grow. For example, soil amendments can help roots more easily penetrate the surrounding soil or could help improve water infiltration. Even if the soil amendments are natural or inorganic, they change the soil in a way that affects the availability of nutrients and the composition of the soil. 

Can I apply soil amendments to the existing soil?

Yes, you can apply it to the existing garden soil. Soil amendments will help add drainage capabilities, add nutrients to the soil, aid in moisture retention, and aid in maintaining the proper pH balance. Among the most frequently used soil amendments are the following: compost, perlite, and vermiculite. 

Which Soil amendments have good water retention capacity?

Organic soil amendments like coconut coir, peat moss, or inorganic soil amendments such as vermiculite, will retain water in the soil and keep it for plants to use when it’s dry. Soil amendments also improve the structure, aeration, and overall health of the soil, which means that your garden will be more successful in the long run if you add them to it.

Conclusion

Soil amendments are great organic fertilizers for garden soils.

Different amendments contain different concentrations of NPK, along with all the micronutrients.

Therefore, it would be best to mix all the amendments and then apply them to the topsoil.

You can even mix the organic matter with the conditioners to improve the nutrient density.

References

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