THEORY AND PRACTICE OF SILICON FERTILIZERS
E.A. Bocharnikova1 , V.V. Matichenkov2,
Institute Physical-Chemical and Biological Problems in Soil Science Russian Academy of Sciences, Pushchino,
142290, Russia, [email protected]
2
Institute Basic Biological Problems Russian Academy of Sciences, Pushchino, 142290, Russia,
[email protected]
1
Abstract: Silicon is the second widespread element on the Earth after oxygen. Besides inert
forms of silicon (quartz, glass et al.), biogeochemically active forms of Si present in nature:
monosilicic, polysilicic acids and organosilicon compounds. Silicon plays a distinctive and
significant role in soil formation processes, affecting soil properties and plant nutrition.
Beginning in 1840 numerous experiments have shown benefits of Si fertilization for crop
productivity. Si fertilizers and Si soil amendments promote restoration of degraded soils as well
as increased soil fertility. Silicon soil amendments provide reduction in Al toxicity in acid soils
more effectively than lime. Silicon improves plant P nutrition. Active Si has a positive influence
on soil microbial population. Plant adsorbs Si in the amounts higher than those of nitrogen,
potassium, and phosphorus. Adsorption of Si is realized with specific transport proteins. High
concentrations of monosilicic acid (150 to 500 ppm of Si) and polysilicic acid (800 to 5000 ppm
of Si) are tested in plant tissue. Numerous studies have been demonstrated that optimization of
plant Si nutrition protects cultivated plants against diseases, fungi and insects attacks without
negative effects on the environment. The main function of Si in plant seems to be a formation of
the natural plant defense system to be realized on several mechanisms. Silicon accumulated in
epidermal tissues forms “a shield” that protects and mechanically strengthens plant. Polysilicic
acid can provide reinforcing biosynthesis of anti-stress hormones and substances. The
application of Si fertilizers or/and Si soil amendments benefits productivity and sustainability of
agriculture.
Key Words: Monosilicic acid, polysilicic acid, plant nutrition, drought, salt toxicity, technology.
Introduction
Beginning in 1848, numerous laboratory, greenhouse and field experiments have shown
benefits of Si fertilization for rice (Oryza sativa L.) (15 to100%), corn (Zea mays L.) (15 to35%),
wheat (Triticum aestivum L.) (10 to 30%), barley (Hordeum vulgare L.), sugar cane (Saccharum
officinarum L,), cucumber (Cucumis sativus L.) (10 to 40%), strawberry (Fragaria spp.) (20 to
30%), citrus (Citrus spp.) (15 to 50%), tomato (Lycopersicon esculentum Mill.) (15 to 50%),
grasses (Stenotaphrum secundatum Kuntze, Cynodon dactulon L., Lolium multiforum L.) (10 to
25%) et al. (Snyder et al. 2006). Silicon fertilization has a double effect on the soil-plant system.
Firstly, improved plant Si nutrition reinforces plant protective properties against diseases, insect
attacks, and unfavorable climatic conditions such as drought, salt, heavy metal or hydrocarbon
toxicity. Secondly, 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 theoretical prerequisites for the first investigations of silicon fertilizers were found in
the end of 18th century. In 1819, Sir Humphrey Davy wrote “The siliceous epidermis of plants
serves as support, protects the bark from the action of insects, and seems to perform a part in the
economy of these feeble vegetable tribes (Grasses and Equisetables) similar to that performed in
the animal kingdom by the shell of crustaceous insects”. In 1840, Justius von Leibig suggested
using sodium silicate as a Si fertilizer and conducted the first greenhouse experiments on this
subject with sugar beets. Starting in 1856 and being continued at present, a field experiment at
the Rothamsted Station (England) has demonstrated a marked effect of sodium silicate on grass
productivity (Rothamsted 1979).
1
In the 19th and 20th centuries, many naturalists measured the elemental composition of
plants. Their data has shown that plants usually contain Si in amounts exceeding those of other
elements (Kovda 1956). Today numerous researches have demonstrated a possibility to raise
crop production on various soils in different climatic zones including extremely dry sub-tropic
(Ahmad et al. 1992) and humid tropic regions (Datnoff et al. 1997).
Si Chemistry
Si is one of the most widely distributed elements in the Earth’s crust, and in turn soil is
the most enriched with silica layer of the Earth’s crust – 40 to 70 % of SiO2 are contained in clay
soils and 90 to 98% in sandy soils. Mainly, Si is present as quartz, alkali and aluminum silicates,
they form a soil skeleton and are chemically or biochemically inert (Perelman et al. 1989). In the
classification of elements on their mobility, Si is defined both as an inert element and as a mobile
element (Perelman et al. 1989). Mobile Si substances represent monosilicic acid, polysilicic acid,
organosilicon compounds, and complex compounds with organic and inorganic substances
(Matichenkov et al. 2001).
Monosilicic acid possesses high chemical activity (Iler 1979, Lindsay 1979). Monosilicic
acid can react with aluminum, iron, and manganese with the formation of slightly soluble
silicates (Lumsdon & Farmer 1995):
Al2Si2O5 + 2H+ + 3H2O = 2Al3+ + 2H4SiO4
Al2Si2O5(OH)4 + 6H+ = 2Al3+ + 2H4SiO4 + H2O
Fe2SiO4 + 4H+ = 2Fe2+ + 2H4SiO4
MnSiO3 + 2H+ + H2O = Mn2+ + 2H4SiO4
Mn2SiO4 + 4H+ = 2Mn2+ + H4SiO4
Monosilicic acid under different concentrations is able to combine with heavy metals
(Cd, Pb, Zn, Hg, and others) forming soluble complex compounds if monosilicic acid
concentration is low (Schindler et. al. 1976) and slightly soluble heavy metal silicates when the
concentration of monosilicic acid is higher in the system (Cherepanov et al. 1994, Lindsay
1979).
ZnSiO4 + 4H+ = 2Zn 2+ + H4SiO4
PbSiO4 + 4H+ = 2Pb 2+ + H4SiO4
The anion of monosilicic acid [Si(OH)3]- can replace the phosphate anion [HPO4]2- from
calcium, magnesium, aluminum, and iron phosphates (Matichenkov & Ammosova 1996).
Besides monosilicic acid, polysilicic acid is an integral component of the natural solution
as well. The mechanism of polysilicic acid formation is not clearly understood (Matichenkov et
al. 1995). Unlike monosilicic acid, polysilicic acid is chemically inert and basically acts as an
adsorbent and forms colloidal particles (Jacinin 1994).
n(Si(OH)4) → (SiO2) + 2n (H2O) or
[SinO2n-(nx/2)(OH)nx] + mSi(OH)4 = [Sin + mO2n-(n2x/2 + 2m(2-p)(OH)nx + 4m - p]
Polysilicic acids are readily sorbed by minerals and form siloxane bridges (Chadwik et al.
1987). Since polysilicic acids are highly water saturated, they may have an effect on the soil
water holding capacity. Polysilicic acids have been found to be important for formation of soil
structure (Matichenkov et al. 1995). There is a pressing need to obtain additional information
about biogeochemically active Si-rich substances involved in the soil formation processes.
Besides mono- and poly-silicic acids, organosilicon compounds are present in soil, water
systems and living organism tissues (Voronkov et al. 1978). The occurrence of organosilicon
substances and their classification is discussed now.
Si and Soil Fertility
The application of Si soil amendments has a positive effect on the chemical and physical
properties of cultivated soils. Most investigations of Si soil amendments or Si fertilizers in soil
concern their interaction with phosphates (Matichenkov & Ammosova 1996).
2
The thermodynamic calculations showed that the reaction of displacing phosphate-anion
by silicate-anion from slightly soluble phosphates and formation of the corresponding silicates is
possible (Matichenkov & Ammosova 1996). Model and field experiments conducted in several
countries have completely confirmed this suggestion (O'Relly & Sims 1995, Singh & Sarkar
1992).
CaHPO4 + Si(OH)4 = CaSiO3 + H2O + H3PO4
2Al(H2PO4)3 + 2Si(OH)4 + 5H+ = Al2Si2O5 + 5H3PO4 + 5H2O
2FePO4 + Si(OH)4 + 2H+ = Fe2SiO4 + 2H3PO4
Our laboratory and field tests have demonstrated that the application of Si fertilizer positively
effects the content of plant-available P in soil (Table 1) (Matichenkov 2008, Matichenkov et al.
2000, Matichenkov et al. 2005). Silicon fertilizers optimize plant P nutrition without the
application of P fertilizer. In practice, this phenomenon gives possibility to reduce rate of
traditional P fertilizers by 25 to 50% without a negative influence on yield.
On the other hand, Si fertilizers or Si soil amendments usually possess good adsorption
capacity. Our field demonstrations on sandy soils (deep sandy Entisol) in Florida have shown
that the application of Si soil amendment provides reduction in the P leaching by 200-300% and
it is important to note that P remains in plant-available forms (Fig. 1) (Chimney et al. 2007). The
leaching of N, K and organic matter reduced under application of Si soil amendment as well
(Matichenkov et al. 2000).
Active Si compounds initiate the formation of the secondary clay minerals in the soil and
increase water-holding capacity, exchange capacity and improve soil texture (Matichenkov et al.
1995). Laboratory and field studies indicate that application of active Si could reduce a rate of
irrigation water application by 20-30 % without negative effect on the plant viability and
productivity (Matichenkov & Bocharnikova 2003).
Considering that monosilicic acid reacts with mobile Al, active Si can reduce the Al toxicity
in acid soils more effectively than lime (Myhr & Erstad 1996, Haak & Siman 1992). It is
possible to postulate five different mechanisms of Al toxicity reduction by Si-rich compounds. 1)
Monosilicic acid can increase soil pH (Lindsay 1979). 2) Monosilicic acids can be adsorbed by
aluminium hydroxides impairing their mobility (Panov et al. 1982). 3) Monosilicic acid can form
slightly soluble substances with ions of aluminum (Lumsdon & Farmer 1995). 4) Mobile
aluminum can be adsorbed by silica surface (Schulthess & Tokunda 1996). 5) Silicon can
increase plant tolerance to Al toxicity (Rahman et al. 1998). All these mechanisms may work
simultaneously with prevailing one or another under determined soil conditions.
The combination of Si soil amendments with active organic substances such as humic
compounds or other sources of organic matter give possibility to create the soil high in fertility
or spot soil degradation processes (Matichenkov et al. 1998). Active Si has a direct positive
effect on clay mineral formation while humic compounds have a positive influence on
humification. The formation of soil organo-mineral complex from Si-rich and organic substances
to improve physical and chemical soil properties and soil structure is a background of this
technology.
Soil microorganisms increase the fixation of nitrogen from the atmosphere, in turn silicon
fertilizers accelerate microbial activity in the soil (Biel et al. 2008).
Si and Plant
Plant absorbs Si from the soil solution in the form of monosilicic acid also called orthosilicic
acid [H4SiO4] (Yoshida 1975). Tissue analyses from a wide variety of plants found Si
concentrations to range from 0.1% to 10% of dry weights depending on plant species (Epstein
1999). Comparison of these values with those for such elements as P, N, Ca, and others shows Si
to be present in amounts equivalent to those of macronutrients.
Mainly Si adsorbed is concentrated in epidermal tissue (Yoshida 1975). Monosilicic acid
accumulated transforms into polysilicic acid and amorphous silica that can associate with pectin
and calcium ion (Waterkeyn et al. 1982). By this means, the double cuticular layer forms
3
protecting and mechanically strengthening plants. The effect of Si fertilizer on plant resistance to
diseases, insect and fungi attacks is explained by this mechanism (Datnoff et al. 1997, Hodson &
Sangster 1988).
Today Si fertilization is recognized as environmentally friendly alternative for pesticides and
fungicides (Datnoff et al. 1997).
Optimization of Si nutrition results in increasing weight and volume of roots, total and
adsorbing surfaces (Adatia & Besford 1986, Bocharnikova 1996). Silicon fertilizer perfects root
respiration (Yamaguchi et al. 1995). The lack in Si nutrition has a negative effect on flowering
and fruit formation (Miyake 1993, Savant et al. 1997).
Silicon may alleviate salt stress in higher plants (Liang 1999, Matichenkov et.al. 2001). For
example, the irrigation by NaCl-bearing solution reduced the biomass of 3-week old barley from
1.05 to 0.66 g for 10 fresh shoots as compared with control. The application of active Si (liquid
or solid forms) increased the biomass of plants under and without salt stresses by 5 to 64% (Fig.
2). Several hypotheses have been suggested to explain this effect. They are (i) improved
photosynthetic activity, (ii) enhanced K:Na selectivity ratio, (iii) increased enzyme activity, and
(iv) increased concentration of soluble substances in the xylem, which results in reduced sodium
adsorption by plants (Liang 1999, Matichenkov et al. 2001).
The interaction between monosilicic acid and heavy metals, aluminum, and manganese
(discussed below) helps to clarify the mechanism by which heavy metal toxicity is reduced
(Barcelo et al. 1993, Foy 1992).
Si in Sustainable Agriculture
Using soil under cultivated plants destroys a balance of nutrients through their annual
harvesting with crop. The active Si removal from cropland ranges from 40 to 300 kg Si per ha.
Totally about 210-224 million ton of Si are harvested with crop from arable soils annually
(Matichenkov & Bocharnikova 1994).
Increasing Si deficit causes a number of negative
consequences for soil and plant. Silicon is a constructive soil element; its lack leads to soil
fertility degradation. The desilication of such minerals as montmorillonites or vermiculites leads
to their transforming to sesquioxides and kaolinites (Savant et al. 1997). In the result, the soil
texture, exchange capacity, water-holding capacity, and other properties are deteriorated.
Plants without sufficient Si nutrition are not able to create effective defense against
abiotic and biotic stresses. Pesticides, fungicides, biostimulators, and overfertilization are
necessary requirements of agricultural production in the absence of proper Si management. At
present, the Si fertilizer demands of the world agriculture are estimated to reach about 700
million ton. The main problem concerning the Si fertilizer implementation is scanty information
being disseminated on the benefits of using Si-rich materials as a fertilizer.
Conclusion
Practical implication of Si fertilizers provides the following benefits:
1) Si increases crop production and quality,
2) Si promotes restoration of degraded soils and increases soil fertility,
3) Si increases soil resistance to wind and water erosion,
4) Si increases plant drought resistance,
5) Si neutralizes Al toxicity in acid soils,
6) Si increases plant P nutrition,
7) Si reduces P, N and K leaching from cultivated areas,
8) Si increases plant salt tolerance,
9) Si protects plant against diseases, insect and fungi attacks,
10) Si restores heavy metal and hydrocarbon-polluted areas,
11) Si promotes biosolid utilization,
12) Si increases productivity in horticulture.
4
The main problem concerning the Si fertilizer implementation in the world is scanty
information being disseminated on the benefits of using Si-rich materials as a fertilizer.
References
Adatia MH, Besford RT. 1986. The effects of silicon on cucumber plants grown in
recirculating nutrient solution. Annals of Botany 58:343-351.
Barcelo J, Guevara P, Poschenrieder C. 1993. Silicon amelioration of aluminum toxicity in
teosinte (Zea mays L. ssp. mexicana). Plant Soil 154: 249-255.
Biel KY, Matichenkov VV, Fomina IR. 2008. Protective role of silicon in living systems. In
Functional foods for chronic diseases. Advances in the Development of Functional Foods
(Martirosyan DM, ed.). Richardson, Texas: Copyright © by D&A Inc., 3: 208-231.
Bocharnikova EA. 1996. The study of direct silicon effect on root demographics of some
cereals. In Proceedings 5th symposium international society root research “The root
demographics and their efficiencies in sustainable agriculture, grasslands, and forest
ecosystems”. South Carolina, p. 84.
Chadwick OA, Hendriks DM, Nettleton WD. 1987. Silica in durick soil. Soil Science
Society of America Journal 51: 975-982.
Cherepanov KA, Chernish GI, Dinelt VM, Suharev JI. 1994. The utilization of secondary
material resources in metallurgy. Moscow: Metallurgy Press.
Chimney MJ, Wan Yongshan, Matichenkov VV, Calvert DV. 2007. Minimizing phosphorus
release from newly flooded organic soils amended with calcium silicate slag: a pilot study.
Wetlands Ecology Management 15: 385–390.
Datnoff LE, Deren CW, Snyder GH. 1997. Silicon fertilization for disease management of
rice in Florida. Crop Protection 16: 525-531.
Epstein E. 1999. Silicon. Annual Review Plant Physiology and Plant Molecular Biology 50:
641-664.
Foy CD. 1992. Soil chemical factors limiting plant root growth. Advances in Soil Science
19: 97-149.
Haak E, Siman G. 1992. Field experiments with Oyeslag (Faltlorsok med Oyeslag). Report
185. Uppsala.
Hodson MJ, Sangster AG. 1989. X-ray microanalysis of the seminal root of sorghum bicolor
with particular reference to silicon. Annals of Botany 64: 659-675.
Iler RK. 1979. The chemistry of silica. New York: John Wiley & Sons .
Jacinin NL. 1994. Colloid-highmolecylar systems in north Kazahstan solonetz. Doctoral
dissertation. Tashkent: Uzbekistan Univerity Press.
Kovda VA. 1956. The mineral composition and soil formation. Pochvovedenie 1:6-38.
Leibigh J. 1840. Organic chemistry in its application to agriculture and physiology. London:
Taylor and Walton.
Liang Y. 1999. Effects of silicon on enzyme activity and sodium, potassium and calcium
concentration in barley under salt stress. Plant Soil 209: 217-224.
Lindsay WL. 1979. Chemical equilibria in soil. New York: John Wiley & Sons.
Lumsdon DG, Farmer VC. 1995. Solubility characteristics of proto-imogolite sols: how
silicic acid can detoxify aluminum solutions. European Soil Science 46: 179-186.
Matichenkov VV. 2008. Role of mobile silicon compounds in the soil-plant system. Doctoral
dissertation. Pushchino.
Matichenkov VV, Ammosova YM. 1996. Effect of amorphous silica on soil properties of a
sod-podzolic soil. Eurasian Soil Science 28: 87-99.
Matichenkov VV, Bocharnikova EA. 1994. Total and partial biogeochemistry cycle of Si in
various ecosystems. In Sustainable development: the view from the less industrialized countries
(Monge-Najera J., ed.). San Jose, Costa Rica: UNEP, pp. 467-481.
5
Matichenkov VV, Bocharnikova EA. 2001. The relationship between silicon and soil
physical and chemical properties. In Silicon in agriculture (Datnoff LE, Snyder GH, Korndorfer
GH, eds). Amsterdam, The Netherlands: Elsevier, pp. 209-219.
Matichenkov VV, Bocharnikova EA. 2003. New technologies for optimization and reduction
of irrigation water application rates. In Proceedings of the international exhibition and
conference for water technology “Water Middle East”. Bahrain: Bahrain Convention &
Exhibition Bureau, pp. 343-352.
Matichenkov VV, Pinsky DL, Bocharnikova EA. 1995. Influence of mechanical compaction
of soils on the state and form of available silicon. Eurasian Soil Science 27: 58-67.
Matichenkov VV, Calvert DV, Snyder GH, Whalen B, Wan Y. 2000. Nutrients leaching
reduction by Si-rich substances in the model experiments. In Proceedings 7th international
conference wetland systems for water pollution control. Lake Buena Vista, Florida, pp. 583-592.
Matichenkov VV, Putsykin YG, Shapovalov AA, Shulgin AI. 1998. The creation and
restoration of potential soil fertility. FAO seminar. Moscow, Russia: Special Biological Physical
Technologies Corp.
Matichenkov VV, Snyder GH, Calvert DV. 2005. Minimizing nutrient and pollutants
leaching from sandy agricultural soils and optimization of plant nutrition. Final report. Florida
Department of Environmental Protection, Florida, USA.
Miyake Y. 1993. On the environmental condition and nitrogen source to appearance of
silicon deficiency of the tomato plant. Scientific report of the faculty of Agriculture Okayama
University. Japan, 81:27-35.
Myhr K., Erstad K. 1996. Converter slag as a liming material on organic soils. Norwegian
Journal of Agricultural Science 10: 81-93.
O’Relly SE, Sims JT. 1995. Phosphorus adsorption and desorption in a sandy soil amended
with high rates of coal fly ash. Communication Soil Science and Plant Analysis 26:2983-2993.
Panov NP, Goncharova NA, Rodionova LP. 1982. The role of amorphous silicic acid in
solonetz soil processes. Vestnik Agricultural Science 11:18-27.
Perelman AI. 1989. Geochemistry. Moscow, Russia:Visshaja Shkola Press.
Rahman MT, Kawamura K, Koyama H, Hara T. 1998. Varietal differences in the growth of
rice plants in response to aluminum and silicon. Soil Science Plant Nutrition 44:423.
Rothamsted Experimental Station. 1991. Guide the Classical Experiment. Watton, Norfolk:
Lawes Agricultural Trust, Rapide Printing.
Savant NK, Snyder GH, Datnoff LE. 1997. Silicon management and sustainable rice
production. Advanced Agronomy. San Diego, USA: Academy Press, 58:151-199.
Schindler PW, Furst B, Dick R, Wolf PO. 1976. Ligand properties of surface silanol groups.
I. Surface complex formation with Fe3+,Cu2+, Cd3+, and Pb2+. Journal of Colloid and Interface
Science 55: 469-475.
Schulthess CP, Tokunaga S. 1996. Metal and pH effects on adsorption of poly(vinil alcohol)
by silicon oxide. Soil Science Society American Journal 60: 92-98.
Singh KP, Sarkar MC. 1992. Phosphorus availability in soil as affected by fertilizer
phosphorus, sodium silicate and farmyard manure. Journal Indian Society of Soil Science 40:
762-767.
Snyder GH, Matichenkov VV, Datnoff LE. 2006. Silicon. In Handbook of Plant Nutrition.
USA: Massachusetts University Press, pp. 551–568.
Voronkov MG, Zelchan GI, Lykevic AY. 1978. Silicon and life. Riga: Zinatne Press.
Waterkeyn L, Bientait A, Peeters A. 1982. Callose et silice epidermiques rapports avec la
transpiration culticulaire. La Cellule 73:263-287.
Yamaguchi T, Tsuno Y, Nakano J, Mano P. 1995. Relationship between root respiration and
silica:calcium ratio and ammonium concentration in bleeding sap from stem in rice plants during
the ripering stage. Japan Journal Crop Science 64:529-536.
Yoshida S. 1975. The physiology of silicon in rice. Technical Bulletins. Taiwan: Food &
Fertilizer Technological Center, 25.
6
Table 1. Effect of Si fertilization on the content of plant-available P in soil.
Soil, location
Plant-available P (0.1 n HCl extraction), mg/kg
Before Si application
After Si application
37.9±2.7
59.6±1.5
28.2±1.4
42.4±3.5
11.0±0.6
14.6±0.6
63.8±3.5
104.8±6.8
16.2±1.1
36.6±2.5
15.3±1.0
46.0±3.1
123±13
142±12.5
13.2±0.3
23.9±1.4
Soddy podzolic soil, Moscow region, Russia
Chestnut soil, South Russia
Mullisoil, South Russia
Alluvial soil, Jordan river valley
Gray Soil, Tajikistan
Calcareous soil, Andalusia, Spain
Spodosol, Florida, USA
Histosol, Florda, USA
7
Figure 1. The content of leacheable P (water-extractable) in sandy soil treated or untreated with
Si soil amendments.
8
Figure 2. The effect of active Si on plant salt tolerance of 3-week old barley.
9