Soil conditioner

A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. 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 fertilizers and non-organic materials.^[1] 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. They can make poor soils more usable, and can be used to maintain soils in peak condition.^[2]

Composition

A wide variety of materials have been described as soil conditioners due to their ability to improve soil quality. Some examples include biochar,^[3] bone meal, blood meal, coffee grounds, compost, compost tea, coir, manure,^[4] straw, peat, sphagnum moss, vermiculite, sulfur, lime, hydroabsorbant polymers,^[5] and biosolids.^[6]

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.^[7]

Polyacrylamides

Polyacrylamides have been widely investigated as soil conditioners.^[8] They were introduced as "linear soil conditioner" in the 1950s by Monsanto Company 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 polyacrylamide 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:^[9]

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, in order to protect the water quality of nearby rivers and streams.^[10] As an nonionic monomer it can be co-polymerize with anionic for example Acrylic acid and cationic monomer such as diallyldimethyl ammonium chloride (DADMAC) and resulted co-polymer that can have different compatibility in different applications.

Polyacrylamide is also used in some potting soil.^[11] Another use of polyacrylamide is as a chemical intermediate in the production of N-methylol acrylamide and N-butoxyacrylamide.^[12]

Purpose

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.^[13]

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.^[14]

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.^[15]^[16]

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.^[17] 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.^[18] 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.^[19]^[20]

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.^[21]

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.^[22]

References

^ "Glossary of Soil Science Terms". Soil Science Society of America. Retrieved May 10, 2012.
^ Noble, R (March 2011). "Risks and benefits of soil amendment with composts in relation to plant pathogens". Australasian Plant Pathology. 40 (157): 157–167. doi:10.1007/s13313-010-0025-7. S2CID 8999229.
^ Kavitha, Beluri; Reddy, Pullagurala Venkata Laxma; Kim, Bojeong; Lee, Sang Soo; Pandey, Sudhir Kumar; Kim, Ki-Hyun (2018). "Benefits and limitations of biochar amendment in agricultural soils: A review". Journal of Environmental Management. 227: 146–154. doi:10.1016/j.jenvman.2018.08.082. PMID 30176434. S2CID 52168678.
^ Bolan, Nanthi; Adriano, Domy; Mahimairaja, Santiago (2004). "Distribution and Bioavailability of Trace Elements in Livestock and Poultry Manure By-Products". Critical Reviews in Environmental Science and Technology. 34 (3): 291–338. Bibcode:2004CREST..34..291B. doi:10.1080/10643380490434128. S2CID 97016838.
^ Guilherme, Marcos R.; Aouada, Fauze A.; Fajardo, André R.; Martins, Alessandro F.; Paulino, Alexandre T.; Davi, Magali F.T.; Rubira, Adley F.; Muniz, Edvani C. (2015). "Superabsorbent hydrogels based on polysaccharides for application in agriculture as soil conditioner and nutrient carrier: A review". European Polymer Journal. 72: 365–385. doi:10.1016/j.eurpolymj.2015.04.017. hdl:11449/172035.
^ "Questions and Answers on Land Application of Biosolids" (PDF). Water Environment Federation. Archived from the original (PDF) on 4 April 2015. Retrieved 24 April 2015.
^ "Natural Fertilizers Amendments". Archived from the original on April 24, 2012. Retrieved May 10, 2012.
^ Friedman, Mendel (2003). "Chemistry, Biochemistry, and Safety of Acrylamide. A Review". Journal of Agricultural and Food Chemistry. 51 (16): 4504–4526. doi:10.1021/jf030204+. PMID 14705871.
^ Arthur Wallace, Sheldon D. Nelson (1986). "Foreword". Soil Science. 141 (5).
^ Construction Contract Standards [1] "Standard Specifications State of California".
^ Environment Canada; Health Canada (August 2009). "Screening Assessment for the Challenge: 2-Propenamide (Acrylamide)". Environment and Climate Change Canada. Government of Canada.
^ Dotson, GS (April 2011). "NIOSH skin notation (SK) profile: acrylamide [CAS No. 79-06-1]" (PDF). DHHS (NIOSH) Publication No. 2011-139. National Institute for Occupational Safety and Health (NIOSH).
^ "Soil Compaction: Causes, Effects, and Control". Archived from the original on May 29, 2012. Retrieved May 10, 2012.
^ "Soil Amendments and Fertilizers" (PDF). Archived from the original (PDF) on May 26, 2012. Retrieved May 10, 2012.
^ "Fundamentals of Soil Cation Exchange Capacity (CEC)". Retrieved May 10, 2012.
^ "What is Soil Conditioner?". Retrieved February 18, 2013.
^ "Improving Your Soil". Retrieved May 10, 2012.
^ Architectural Graphic Standards. The American Institute of Architects. 2008. p. 18. ISBN 9780470085462.
^ Lees, David (May 2021). "Permeation Grouting in Sydney". Conference: Geotechnical Advances and Challenges in Urban Development. ...application is limited by the soil conditions and whilst ideal in the aeolian sands, it may not be appropriate in the fluvial deposits which are richer in silts and organic matter.
^ "Laboratory Evaluation of Performance and Durability of Polymer Grouts for Subsurface Hydraulic/Diffusion Barriers". UNT Digital Library. Brookhaven National Laboratory. 1994. The selection of subsurface barriers for any given site which needs remediation, and the selection of a particular barrier technology must be done, however, by means of the Superfund Process, with special emphasis on the remedial investigation and feasibility study portions. The chemical compatibility of the material with the wastes, leachates and geology with which it is likely to come in contact is of particular importance for barriers constructed from fluids which are supposed to set in-situ. EPA emphasizes this compatibility in its guidance documents, noting that thorough characterization of the waste, leachate, barrier material chemistry, site geochemistry, and compatibility testing of the barrier material with the likely disposal site chemical environment are all required.
^ "Producing Garden Vegetables with Organic Soil Amendments". Archived from the original on May 23, 2000. Retrieved May 10, 2012.
^ "Protecting Water Quality from Agricultural Runoff" (PDF). Retrieved May 10, 2012.