What are the Different Types of Soil Amendments?

C. K. Lanz

Soil amendments are typically divided into two categories or types: inorganic or man-made and organic or made with naturally occurring products. Each type has its specific uses and benefits as well as its detriments. Organic soil amendments are generally made from straw, leaves, and biosolids. Compost and peat and are used to fertilize and prevent pest infestation. Amendments that are man-made or inorganic include tire pieces, pea gravel, and sand and can over time deplete the soil’s naturally occurring nutrients.

Compost is an organic amendment to improve crop production.
Compost is an organic amendment to improve crop production.

The appropriate type of soil amendment depends on the particular needs, texture, and salinity of the soil and the types of crops and flowers that will be grown. For example, sandy soil often benefits from the addition of an amendment like peat that will increase moisture retention. Clay soil may require an amendment that will improve aeration and therefore should not be mixed with sand.

Need will dictate the appropriate types of soil amendments to use.
Need will dictate the appropriate types of soil amendments to use.

Soil amendments made from organic materials can work as organic fertilizers as they improve the soil’s properties. A constant and stable supply of nutrients will encourage healthy plant growth. Helpful fungi, bacteria, and worms rely on organic matter in the soil for energy and will break down organic soil amendments.

Grass clippings are a form of organic soil amendments.
Grass clippings are a form of organic soil amendments.

Some of the organic soil amendments that decompose the quickest are manure and grass clippings. These amendments will begin to decompose within a few days and can improve soil fast. Composts, peat, and wood chips decompose far more slowly and are useful when the goal is to achieve soil improvement that is long lasting.

Sand can be added to soil to improve drainage.
Sand can be added to soil to improve drainage.

Small particles of rubber tires are a common non-organic soil amendment that help improve the porosity of soil. Both perlite and vermiculite are usually mixed with potting soil to boost oxygenation. Pea gravel can loosen clay soil so that water and air can reach plant roots. Sand can also improve drainage.

Fertilizer is a commonly used form of soil amendment.
Fertilizer is a commonly used form of soil amendment.

Inorganic soil amendments can quickly improve the physical properties of soil such as drainage and porosity but will add few nutrients other than macro nutrients like nitrogen, phosphorus, and potassium. Organic soil amendments may break down at a slower pace but can provide many secondary and trace nutrients and minerals while feeding helpful soil organisms. Soil amendments made from organic materials are often more environmentally friendly than non-organic products.

Clay soil can be mixed with gravel to improve aeration.
Clay soil can be mixed with gravel to improve aeration.

The appropriate amount of a soil amendment should be well mixed into the ground in order to improve the soil’s physical properties and create an environment conducive to root growth. The effectiveness of soil amendments that are lightly covered with soil is impaired. Scattering a product on the surface is actually mulching and will slow evaporation and weed germination as well as help keep soil temperature constant.

Earthworms break down the organic matter in soil.
Earthworms break down the organic matter in soil.

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