A soil conditioner is a product which is added to

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

to improve the soil’s physical qualities, usually its

fertility Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate ...

(ability to provide nutrition for plants) and sometimes its

mechanics Mechanics () is the area of physics concerned with the relationships between force, matter, and motion among Physical object, physical objects. Forces applied to objects may result in Displacement (vector), displacements, which are changes of ...

. In general usage, the term "soil conditioner" is often thought of as a subset of the category soil amendments (or soil improvement, soil condition), which more often is understood to include a wide range of

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

s and non-organic materials. In the context of construction soil conditioning is also called soil stabilization. Soil conditioners can be used to improve poor soils, or to rebuild soils which have been damaged by improper

soil management Soil management is the application of operations, practices, and treatments to protect soil and enhance its performance (such as soil fertility or soil mechanics). It includes soil conservation, soil amendment, and optimal soil health. In agricult ...

. They can make poor soils more usable, and can be used to maintain soils in peak condition.

Composition

A wide variety of materials have been described as soil conditioners due to their ability to improve soil quality. Some examples include

biochar Biochar is a form of charcoal, sometimes modified, that is intended for organic use, as in soil. It is the lightweight black remnants remaining after the pyrolysis of biomass, consisting of carbon and ashes. Despite its name, biochar is steril ...

, bone meal,

blood meal Blood meal is a dry, inert powder made from blood, used as a high-nitrogen organic fertilizer and a high protein animal feed. By weight, it is generally 12% nitrogen with trace amounts (≤1%) of phosphorus and potassium. It is one of the hig ...

, coffee grounds,

compost Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by Decomposition, decomposing plant and food waste, recycling organic materials, and man ...

, compost tea,

coir Coir (), also called coconut fibre, is a natural fibre extracted from the outer husk of coconut, and used in products such as floor mats, doormats, brushes, and mattresses. Coir is the fibrous material found between the hard, internal shell ...

manure Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the fertility of soil by adding organic matter and nut ...

straw Straw is an agricultural byproduct consisting of the dry wikt:stalk, stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the crop yield, yield by weight of cereal crops such as barley, oats, rice, ry ...

peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...

sphagnum moss ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store water, since ...

vermiculite Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently; commercial furnaces can routinely produce this effect. Vermiculite forms by the weathe ...

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

, lime, hydroabsorbant polymers, biosolids, and rock flour. Many soil conditioners come in the form of certified organic products, for people concerned with maintaining organic crops or organic gardens. Soil conditioners of almost every description are readily available from online stores or local nurseries as well as garden supply stores.

Polyacrylamides

Polyacrylamides have been widely investigated as soil conditioners. They were introduced as "linear soil conditioner" in the 1950s by

Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed in ...

under the trade name Krilium. The soil conditioning technology was presented at a symposium on "Improvement of Soil Structure" held in Philadelphia, Pennsylvania on December 29, 1951. The technology was strongly documented and was published in the June 1952 issue of the journal ''Soil Science'', volume 73, June 1952 that was dedicated to polymeric soil conditioners. The original formulation of poly acrylamide soil conditioners was difficult to use because it contained calcium which cross-linked the linear polymer under field conditions. Krilium was abandoned by Monsanto. Water-soluble soil conditioners offer the following benefits: # increase pore space in soils containing clay # increase water infiltration into soils containing clay # prevent soil crusting # stop erosion and water runoff # make friable soil that is easy to cultivate # make soil dry quicker after rain or irrigation, so that the soil can be worked sooner Consequently, these translate into # stronger, larger plants with more extensive root system # earlier seed emergence and crop maturity # more efficient water utilization # easier weed removal # more response to fertilizers and to new crop varieties # less plant diseases related to poor soil aeration # decreased energy requirement for tillage The cross-linked forms of polyacrylamide, which strongly retain water, are often used for horticultural and agricultural under trade names such as Broadleaf P4 and Swell-Gel. In addition to use on farm lands, these polymers are used at construction sites for

erosion control Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development, coast, coastal areas, Bank (geography), river banks and construction. Effective erosion controls handle surface runoff and are ...

, in order to protect the

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

of nearby

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s and streams. As an nonionic monomer it can be co-polymerize with anionic for example Acrylic acid and cationic monomer such as DADMAC and resulted

copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...

that can have different compatibility in different applications. Polyacrylamide is also used in some potting soil. Another use of polyacrylamide is as a chemical intermediate in the production of N-methylol acrylamide and N-butoxyacrylamide.

Purpose

Soil structure

The most common use of soil conditioners is to improve soil structure. Soils tend to become compacted over time.

Soil compaction In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water (or other ...

impedes root growth, decreasing the ability of plants to take up nutrients and water. Soil conditioners can add more loft and texture to keep the soil loose.

Soil nutrients

For centuries people have been adding things to poor soils to improve their ability to support healthy plant growth. Some of these materials, such as compost, clay and

, are still used extensively today. Many soil amendments also add nutrients such as carbon and nitrogen, as well as beneficial bacteria. Additional nutrients, such as calcium, magnesium and

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

, may be augmented by amendments as well. This enriches the soil, allowing plants to grow bigger and stronger.

Cation exchange

Soil amendments can also greatly increase the cation exchange capacity (CEC) of soils. Soils act as the storehouses of plant nutrients. The relative ability of soils to store one particular group of nutrients, the

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

. The most common soil cations are

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

, and

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

. The total number of cations a soil can hold, its total negative charge, is the soil's cation exchange capacity. The higher the CEC, the higher the negative charge and the more cations that can be held and exchanged with plant roots, providing them with the nutrition they require.

Water retention

Soil conditioners may be used to improve water retention in dry, coarse soils which are not holding water well. The addition of organic material for instance can greatly improve the water retention abilities of sandy soils and they can be added to adjust the pH of the soil to meet the needs of specific plants or to make highly acidic or alkaline soils more usable. The possibility of using other materials to assume the role of composts and clays in improving the soil was investigated on a scientific basis earlier in the 20th century, and the term soil conditioning was coined. The criteria by which such materials are judged most often remains their cost-effectiveness, their ability to increase soil moisture for longer periods, stimulate microbiological activity, increase nutrient levels and improve plant survival rates. The first synthetic soil conditioners were introduced in the 1950s, when the chemical hydrolysed

polyacrylonitrile Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin, with the linear formula (CH2CHCN)n. Almost all PAN resins are copolymers with acrylonitrile as the main monomer. PAN is used to produce large variety of products in ...

was the most used. Because of their ability to absorb several hundred times their own weight in water, polyacrylamides and polymethacrylates (also known as hydroabsorbent polymers, superabsorbent polymers or

hydrogel A hydrogel is a Phase (matter), biphasic material, a mixture of Porosity, porous and Permeation, permeable solids and at least 10% of water or other interstitial fluid. The solid phase is a water Solubility, insoluble three dimensional network ...

s) were tested in agriculture, horticulture and landscaping beginning in the 1960s. Interest disappeared when experiments proved them to be phytotoxic due to their high acrylamide monomer residue. Although manufacturing advances later brought the monomer concentration down below the toxic level, scientific literature shows few successes in utilizing these polymers for increasing plant quality or survival. The appearance of a new generation of potentially effective tools in the early 1980s, including hydroabsorbent polymers and copolymers from the propenamide and propenamide- propenoate families, opened new perspectives.

Soil stabilization

In the context of construction there are some soil improvement techniques that are intended to improve the effective strength and resistance of very soft soils, for example when excavating deep tunnels for underground subway or tunnel construction. The soil stabilization technique of low pressure chemical permeation grouting has also been used for high rise foundation underpinning as an alternative to pile foundations at a residential development over the East River landfill. Pressure grouting can be difficult to apply correctly at sites with waste materials or heterogeneous and coarse soils.

Application

Soil conditioners may be applied in a number of ways. Some are worked into the soil with a tiller before planting. Others are applied after planting, or periodically during the growing season. Soil testing should be performed prior to applying a soil conditioner to learn more about the composition and structure of the soil. This testing will determine which conditioners will be more appropriate for the available conditions.

Ecological concerns

While adding a soil conditioner to crops or a garden can seem like a great way to get healthier plants, over-application of some amendments can cause ecological problems. For example, salts, nitrogen, metals and other nutrients that are present in many soil amendments are not productive when added in excess, and can actually be detrimental to plant health. (See fertilizer burn.) Runoff of excess nutrients into waterways also occurs, which is harmful to the water quality and, through it, the environment.