Soil conditioner

Also known as: soil amendment

A soil conditioner is a material added to soil to improve its physical properties, such as structure, aeration, water infiltration and water-holding capacity, rather than to supply nutrients. Examples include compost, gypsum, polymers and soil surfactants.

What is a soil conditioner?

A fertilizer feeds the crop. A soil conditioner improves the soil itself, mainly its physical condition: how well it holds together in crumbs, how easily water and air move through it, and how much water it can store for roots. The terms soil conditioner and soil amendment are often used interchangeably, although soil amendment is also used more broadly for materials that change soil chemistry, such as lime for pH.

Common soil conditioners

Conditioner	Main effect
Compost and manure	Add organic matter, improve structure and water holding
Gypsum	Supplies calcium that helps clay particles group together, improving structure and infiltration, especially in sodic soils
Polyacrylamide polymers	Stabilize soil surfaces and reduce erosion, notably in furrow irrigation
Biochar	Adds a stable, porous carbon material
Soil surfactants	Improve how water wets and moves through soil

What soil conditioners are used for

Improving water infiltration and reducing runoff and crusting.
Improving aeration and root growth in dense or compacted soils.
Increasing water-holding capacity in sandy soils.
Building soil organic matter and supporting soil health.
Reclaiming sodic soils.

Results depend on the soil’s specific problem. A conditioner that fixes a sodic clay may do little for a sandy soil, so diagnosis comes first.

Regulation

In the United States, soil conditioners and amendments are generally regulated by states, often under fertilizer or soil amendment laws that govern labeling and claims. Model definitions developed by the Association of American Plant Food Control Officials are widely used.