Soil structure The most common use of soil conditioners is to improve soil structure. Soils tend to become compacted over time.
Soil compaction 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
peat, 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, 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. The most common soil cations are
calcium,
magnesium,
potassium,
ammonium,
hydrogen, and
sodium. 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 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
hydrogels) 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==