Ameliorative Effect of Silicate in Soil and Plant. A Review
Keywords:Silica, soil, plant, silicates, silicic acid
Silica is the scientific name for a group of minerals made of silicon and oxygen. Silica is found in most mineral deposits in the world in both crystalline and non-crystalline (amorphous) forms. Silicon concentrations vary greatly in plant aboveground parts, ranging from 0.1 to 10.0% of dry weight. Silicates soil amendments provide effective and efficient means to correct a number of soil chemical imbalances, nutrient deficiencies and toxicity issues. Soil treatment with biogeochemically active Si substances optimizes soil fertility through improved water, physical and chemical soil properties and maintenance of nutrients in plant-available forms. The amount of Si in soil may vary considerably from 1 % to 45 %. Most Si is present in the soil as insoluble oxides or silicates, but plants can easily absorb silicic acid Si (OH)4 from soil. Silicic acid is generally found in the range of 0.1-0.6 mM in soils. Unfortunately, soluble Si polymerizes rapidly if the concentration of Si increases above 2 mmol L-1. Uptake of Si from external solution and its transport through roots might be an active or a passive (diffusion) process. Once silicon is absorbed by the plant, it actively contributes to a balanced state of nutrient availability through uptake processes and micro-distribution of mineral ions. As a result of increasing silicon concentrations in plant tissues the mechanical strength may be improved. The Si content in plant tissue varies greatly among the species and can range from 0.1 to 10% on a dry weight basis. Rice is a typical Si accumulator and its uptake is about twice that of nitrogen. Application of silicon as a soil amendment has been reported to result in elevated concentrations of chlorophyll per unit area of leaf tissue, resulting in improved photosynthetic efficiency. Si is effective in mitigating salinity in different plant species, (barley, cucumber, tomato). Some possible mechanisms through which silicon may increase salinity tolerance in plants include immobilization of toxic sodium ion and enhanced potassium uptake. In plants growing under salt-stress conditions, added silicon helps in maintaining an adequate supply of essential nutrients and reduces sodium uptake and its transport to shoots. Important aspects of silicon fertilization that have gained interest are increased drought resistance. Reduction of transpiration rate (or increase of leaf resistance) has been attributed to silicon. An alleviative function of Si on Mn toxicity has been observed in rice, barley, and pumpkin. Silicon may be responsible for the alleviation of Zn and Fe excess toxicity in rice roots. Si-enhanced tolerance to Cd and this was attributed that not only to Cd immobilization caused by silicate-induced pH rise in the soils but also to Si-mediated detoxification of Cd in the plants. Several studies have shown that Si is effective in enhancing the resistance to diseases and pests. Silicon reduces the epidemics of both leaf and panicle blast at different growth stages. Silicon has been reported to prevent the incidence of powdery mildew disease, brown spot, and stem rot, sheath brown rot on rice, fusarium wilt, and corynespora leaf spot on cucumber. Silicon suppresses insect pests such as stem borer, brown plant hopper, rice green leaf hopper, and white backed plant hopper, and no insect pests such as leaf spider and mites. It prevents physical penetration and/ or makes the plant cells less susceptible to enzymatic degradation by fungal pathogens.
This work is licensed under a Creative Commons Attribution 4.0 International License.