Soil conditioner- Classification, Usage & Effects on Plants
What is Soil conditioner?
Soil conditioner generally refers to any material or chemical added to a soil solely or in combination to improve plant growth and health typically by improving the soil structure and/or nutrient concentrations.
A soil conditioner is a product which is applied to soil in order to improve the soil’s physical qualities, usually its fertility and also its behaviours. Soil conditioner can make poor soils more usable, and can be used to maintain soils in peak condition, hence it can be used to improve poor soils, or to rebuild soils which have been damaged by improper soil management.
Soil conditioners can be applied to the upper layers of soil, where the root systems normally develop. The use of soil conditioners has been proved effective in providing a reservoir of soil water to plants.
With respect to soil conservation measures, Soil conditioners are products that are applied to control water erosion and improve soil properties. PAMs, phosphogypsum, and flue gas desulfurization (FGD) gypsum etc. are some conditioners used to reduce water erosion. These conditioners have not been widely used in agricultural lands but are used as potential erosion control practices.
There is a vast market for soil conditioners because of their effectiveness. Currently, numerous commercial products are available in the market. They could be of natural or synthetic origin in either solid or liquid phase.
Classification of Soil Conditioners
soil conditioners can be classified based on their origin and composition. The origin of materials can be natural or synthetic, whereas the composition of soil conditioners may be organic or inorganic.
Therefore, soil conditioners may be roughly classified into four categories based on the major ingredient: organic, inorganic, synthetic, and other soil conditioners.
- Organic Soil Conditioners
Materials derived from living organisms such as, plants and animals make up organic soil conditioners. Organic materials as soil amendments have been widely used to improve the soil properties and plant growth. Organic soil conditioners can be applied to improve the infiltration and water retention, promote aggregation, enhance microbial activity, and increase resistance to crusting and compaction of soil with soil organic matter.
Examples: farmyard manure, crop residues, manures, peat, biochar, bone meal, blood meal, coffee grounds, compost tea, coir, sewage sludges, and sawdust.
- Inorganic soil conditioners
These are either mined or manufactured by-products, occurring naturally or synthetically which improve the soil physical properties, thereby enabling the successful utilisation of soil and water resources.
Examples: Gypsum, lime, limestone, pyrites, crushed rocks, fly ash, sulphur, zeolites, dolomite, phosphogypsum.
- Synthetic soil conditioners
Due to short lifespan and high cost of conventional organic soil conditioners; synthetic soil conditioners, which are cheaper and more eco-friendly are now getting attention.
Polymers are typical synthetic soil conditioners and can be applied cost-effectively at a low rate. The compounds are long-chain, polymeric, and organic materials with a very high molecular weight that bind soil particles together and form aggregates. Minor amounts of linear and cross-linked polymers can be used as effective stabilising agents for improving soil water holding capacity because of their low cost and great efficiency in avoiding seal formation, infiltration rate reduction, and soil erosion.
Organic polymers, primarily polysaccharides (PSDs) and polyacrylamides (PAMs), are commonly used to improve aggregate stability, maintain fertility, and reduce seal formation.
- Other soil conditioners
Other industrial wastes, enzymes, microorganisms, and activators are examples of other soil conditioners. Many industrial by-products can be useful for sustainable agricultural productions.
Usage of Soil Conditioner
Mostly soil conditioner is used for following purposes-
- To improve Soil structure: The most common use of soil conditioners is to improve soil structure. Soils tend to become compacted over time that 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.
- To increase Soil Nutrients: to promote healthy plant growth, materials such as compost, clay and peat, are used extensively. 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 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.
- To improve 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.
- 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.
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.
Effects of Soil Conditioners on Soil Properties
Natural and synthetic soil conditioners can both have a tremendous influence on the soil’s physical, chemical, and biological properties. Plant-based by-products play a major role in recycling the essential plant nutrients, sustaining soil fertility and reducing the toxicity of some heavy metals, which lead to increased yield with the proper dosages of the by-products.
- Biochar (organic soil conditioner) directly increases the soil’s pH and organic matter. At the same time, it decreases the bulk density and extractable salt content in soil and increases nitrate availability. Soil amendment using biochar from rice husk, corn cob, and tobacco by-products with organic fertilisers (e.g., compost and chicken manure) improve soil organic matter and the soil’s physical properties. Biochar can potentially enhance soil properties, soil health with microbial abundance, and biological nitrogen fixation, hence, improving agro-ecosystem sustainability in plant production. Moreover, the available nitrate, potassium, and cation exchange capacity (CEC) in the soil are increased accordingly with an increase in the biochar concentrations, while the available phosphate decreases.
- Biomass bottom ash and dolomite-based soil conditioner are proven to improve the availability of P, K, and most other nutrients in the soil. Moreover, the addition of wood ash to soils can act as a liming agent or artificial fertilisers to improve the fertility of agricultural soils, reducing specifically the exchangeable quantities of Al and Mn elements.
- Granular seaweed (Sargassum johnstonii) increases Na, K, Mg, Ca, and Zn in the soil with improved porosity and water holding capacity (WHC) in the tomato production. Seaweed are found to be better utilise N, P, and K for the growth and yield of eggplant (Solanum melongena).
- Composted sewage sludge with liming effectively improves soil health and plant growth, achieving higher rates of OM mineralisation followed by higher respiration rates in amended soils due to decreased soil acidification.
- Bauxite residue (BR), in combination with bio-wastes, improves the physical and chemical characteristics of soil. BR has been applied to manage a variety of problems in soils, including acidity, limited water holding capacity, and phosphorus loss. It is reported that, the addition of BR to degraded acidic sandy soils at a rate of 5% increases pH, WHC, and improves soil texture without significant harmful effects on plants and microorganisms. With the increase of pH in acidic soil, the nutrient availability and microbial activity are improved. Consequently, plants grow better and produce more root exudates as a carbon source available for survival and multiplication of microbes.
- Farmyard manure contains substantial amounts of nutrients as biological soil fertilisers.
- Digestate has been excellent fertiliser with reduced emissions of CH4and N2
- Fly ash has been utilised for soil conditioning to restore the structure, conductivity, and particle size of soil, as well as to reduce bulk density while increasing WHC and conserving the soil from erosion.
- Gypsum increases the macroporosity of soil in the superficial layer.
Effects of Soil Conditioners on Plant Growth & Development
With the addition of soil conditioners, the increased availability of nutrients in the soil enables plants to compete with weeds, pests, and diseases and improves abiotic stress tolerance.
Biochar, household compost, vermicompost, spent mushroom compost (SMC), and farmyard manure are proven to increase tomato yield.
- Biochar enhances plant growth with increased dry matter in the above-ground and root tissue of berseem clover (Trifolium alexandrinum, L.), accompanied by significant reductions in Cr, Cu, Ni, and Pb in the above-ground tissues. The application of biochar to the soil enhanced the fresh matter,dry matter, and leaf number of a leafy vegetable.
- BA amendments found to improve the vegetative growth and edible hypocotyl yield of radish (Raphanus sativus) with increased Cd accumulation in all tissues.
- The application of SMC has proven a significant effect on soybean’s leaf number, leaf area index, height, fresh matter (FM), and dry matter (DM).
- Different types of seaweed extract also found to significantly increase the growth and yield of eggplant.
- Poultry litter pellets were applied as organic fertiliser to promote maize (Zea mays) growth, supplying nutrients from the pellets.
- “UGmax” (soil conditioner) with mineral fertilisation (N, P, K) showed better production of DM, total protein, and soluble carbohydrates in grass species with increased nutrients.
- The total maize dry matter was enhanced using polymeric natural and synthetic soil conditioners with improved water retention ability.
- Soil conditioners play a significant role in the growth and development of plants.