Technical Sheet – Silicates in Plant Nutrition

Introduction: 

Silicates are formed from the element Silicon (Si). Silicon is a beneficial element for higher plants and is found in significant quantities in most plants - amounts comparable to that of phosphorus, calcium and magnesium. Plants can contain silicon at levels higher than any other mineral ¹. Bio-available Silicon is typically absorbed by plants as a Silicate (“monosilicic acid”, H₄SiO₄ - also called “orthosilicic acid”). The Silicon is deposited as silica in the plant cell walls, improving cell wall structural rigidity and strength ², plant architecture and leaf erectness.  

Silicon can stimulate plant photosynthesis, decrease susceptibility to disease and insect damage, and alleviate water and various mineral stresses ^3,4. 

Silicon can decrease the toxic effects of Aluminium ^{5,6,7,8,9,10,11}. Several mechanisms have been proposed to explain Aluminium (Al) detoxification by Silicon :  

·         Silicon binds to aluminium - forming less toxic aluminosilicates ^5,8 (see Fig 1),

·         Silicon increases soil pH - Aluminium is very water soluble & mobile at acid pH’s ⁹. Aluminium precipitates and falls out of solution at pH’s above 4.6 in CaCl₂  ¹⁰; (see Fig 2) and

·         Silicon mediated plant detoxification mechanisms – Silicates added to soils with high Aluminium concentrations can greatly stimulate plant roots to secrete organic acids (eg citrate and malate ⁵) and phenolics (eg catechin and quercetin ¹¹) – these organic exudates can chelate to Aluminium and reduce the activity of free Al ions.

ALUMINIUM and Soil Acidification: 

Soil acidification is a major threat to the sustainability of Western Australia's agricultural industries. About two thirds of WA's wheatbelt soils are either acid or at risk of acidification ¹². Aluminium is a significant contributor to acidification of soils in Western Australia ¹³.  

In many acid soils, aluminium toxicity is one of the major limiting factors of plant growth and development ^14,15,16,17. There is a direct relationship between toxic aluminium concentration in soil  and soil pH - particularly pH’s below 4.6 in CaCl₂ (calcium chloride) ¹⁰. 

Plants grown in aluminium dominated acid soils have impaired root systems and inhibited shoot growth, resulting in a decrease in vigor and yield ^18,19,20,21 and ultimately profitability ²².  Aluminium is reported to interfere with the uptake, transport, and metabolism of several essential nutrients (eg locks-up Phosphorous in less bio-available forms in acid soils); and plants display a variety of nutrient deficiencies ^23,24 (e.g. Phosphorous, Calcium, Magnesium or Fe-Iron) and reduced water uptake ^25,13. 

Western Mineral’s Fertilisers are Silicate based!  

Western Mineral Fertilisers have developed quality silicate based fertilisers.  Materials included in the compound fertiliser granules (pellets) have been specially selected - based upon their plant-available silicates (Calcium Silicate, Potassium Silicates and mineral ore based silicates). Silicate based fertilisers play a key role in plant nutrition, insect and disease resistance ²⁶, soil adsorption capacity, and can optimize physical and structural properties of the soil ^27,28. 

In addition, application of silicate mineral fertilisers increases water holding capacity, cation-exchange capacity and thus nutrient cycling ^29,30,31. The surface of silicate minerals may also provide sites for the formation of organic matter, thereby assisting to increase organic matter levels in deficient and disturbed soils ³². 

WMF Microbe technology has been developed to enhance the performance of these Mineral fertilisers. Microorganisms play an important role in the weathering of silicate minerals and in turn the minerals appear to play an important role in microbial ecology ^33,34,29.  90% of terrestrial plants form symbiotic associations with microorganisms such as mycorrhizal fungi. In these plants, the fungal hyphae of the mycorrhiza perform a vital function in the acquisition of Phosphorous ^35,36, and other mineral nutrients (such as silicates ³⁷) for the plant. 

Conclusion: 

The beneficial effects of bio-available Silicon on plant growth are mainly attributable to the silicates that accumulate in plant cell walls. These effects are demonstrated most clearly under high-density cultivation systems with heavy applications of nitrogen. Silicon is now becoming recognized as an 'agronomically essential element’, as it helps to generate resistance to disease and pests in many plants, and may also reduce rates of application of pesticides and fungicides. Silicon is also considered as an environment-friendly element - in relation to soils, fertilisers and plant nutrition. In addition Silicon uptake (in a bio-available form) is enhanced by good soil microbiology (involving mycorrhiza in particular). 

Western Mineral Fertilisers products (minerals & microbes) are designed & manufactured for the complexities of West Australian soils, and are having a significant positive impact in Agriculture across Western Australia.  Western Mineral Fertilisers recommends & uses only biologically-friendly forms of inputs in our Mineral fertilisers.  WMF’s Plants-Microbe-Mineral-Soil management system assists with more efficient uptake, retrieval and internal use of Silicon (& other nutrients). 

References:  

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2.       Nelwamondo A, Jaffer MA, Dakora FD (2001) Subcellular organization of N2-fixing nodules of cowpea (Vigna unguiculata) supplied with silicon Protoplasma.;216(1-2):94-100.

3.       Epstein E (1999) Silicon. Annu Rev Plant Physiol Plant Mol Biol 50: 641–644.

4.       Ma JF, Miyake Y, Takahashi E (2001) Silicon as a beneficial element for crop plants. In L Datonoff, G, Korndorfer, G Snyder, eds, Silicon in Agriculture. Elsevier Science Publishing, New York, pp 17–39.

5.       Cocker, K.M., Evans, D.E. & Hodson, M.J. (1998) The amelioration of aluminium toxicity by silicon in higher plants: Solution chemistry or an in planta mechanism? Physiol. Plant. 104, 608.614.

6.       Ma JF, Sasaki M, Matsumoto H. (1997) Al-induced inhibition of root elongation in corn, Zea mays L. is overcome by Si addition. Plant Soil 188:171-176.

7.       Zsoldos F, Vashegyi Á, Bona L, Pécsváradi A, Szegletes Zs (2000) Growth and potassium transport of winter wheat and durum wheat as affected by various aluminium exposure times. J Plant Nutr 23:913-926.

8.       Vashegyi, A., Zsoldos, F., Pécsváradi, A., Bona, L. (2002) Aluminium/silicon interactions in cereal seedlings Acta Biologica Szegediensis 46(3-4):129-30.

9.       Simonsson M, Berggren D.(1998) Al solubility related to secondary solid phases in upper B horizons with spodic characteristics. Eur.J.Soil Sci. 49:317-326.

10.   Tang, C., & Rengel, Z. (2001) Liming & Reliming Enhance Barley Yield on Acidic Soil, Bulletin 4509 - WA Soil Acidity Research & Development Update.

11.   Kidd, P.S., Llugany, M., Poschenrieder, C., Gunsé, B. and Barceló, J. (2001) The role of root exudates in aluminium resistance and silicon-induced amelioration of aluminium toxicity in three varieties of maize (Zea mays L.) Journal of Experimental Botany, 52, No. 359, pp. 1339-1352.

12.   Porter, B. (1997)  Bulletin 4505 - Western Australia Soil Acidity Research and Development Update.

13.   Gazey C. and O’Connell, M. (2001) Soil Acidity Management Pays Off, Bulletin 4509 - Western Australia Soil Acidity Research and Development Update.

14.   Delhaize, E. & Ryan, P.R. (1995) Aluminum toxicity & tolerance in plants. Plant Physiol. 107, 315-321.

15.   Horst, W.J. Schmohl, N., Kollmeier, M., Baluska, F. & Sivaguru, M. (1999) Does aluminium inhibit root growth of maize through interaction with the cell wall-plasma membrane-cytoskeleton continuum? Plant Soil 215, 163-174.

16.   Marienfeld, S., Schmohl, N., Klein, M., Schroeder, W.H., Kuhn, A.J. & Horst, W.J. (2000) Localisation of aluminium in root tips of Zea mays and Vicia faba. J. Plant Physiol. 156, 666-671.

17.   Kollmeier, M., Felle, H.H. & Horst, W.J. (2000) Genotypical differences in aluminum resistance of maize are expressed in the distal part of the transition zone. Is reduce basipetal auxin flow involved in inhibition of root elongation by aluminum? Plant Physiol. 122, 945-956.

18.   Mossor-Pietraszewska, T., Kwit, M. & Legiewicz, M. (1997) The influence of aluminium ions on activity changes of some dehydrogenases & aminotransferases in yellow lupine. Biol. Bull. Poznan 34, 47-48.

19.   Nosko, P., Brassard, P., Kramer, J.R. & Kershaw, K.A. (1988) The effect of aluminum on seed germination and early seedling establishment, growth and respiration of white spruce (Picea glauca). Can. J. Bot. 66, 2305-2310.

20.   Blancaflor, E.B., Jones, D.L. & Gilroy, S. (1998) Alterations in the cytoskeleton accompany aluminum-induced growth inhibition and morphological changes in primary roots of maize. Plant Physiol. 118, 159-172.

21.   Taylor, G.J., Blamey, F.P.C. & Edwards, D.G. (1998) Antagonistic and synergistic interactions between aluminum and manganese on growth of Vigna unguiculata at low ionic strenght. Physiol. Plant. 104, 183-194.

22.   Sandison, A. & Bathgate, A. (1997) Bulletin 4505 - Western Australia Soil Acidity Research and Development Update.

23.   Foy, C.D. (1988) Plant adaptation to acid, aluminum-toxic soils. Commun. Soil Sci. Plant Anal. 19, 959-987.

24.   Huang, J.W., Pellet, D.M., Papernik, L.A. & Kochian, L.V. (1996) Aluminum interactions with voltage-dependent calcium transport on plasma membrane vesicles isolated from roots of aluminum-sensitive and -resistance wheat cultivars. Plant Physiol. 110, 561-569.

25.   Gunse, B., Poschenrieder, Ch. & Barcelo, J. (1997) Water transport properties of roots and root cortical cells in proton- and Al-stressed maize varieties. Plant Physiol. 113, 595-602.

26.   Datnoff, L.E., Deren, C.W., Snyder, G.S. (1997) Silicon Fertilization for Disease Management of Rice in Florida. Crop Protection. 16, 6, 525-531

27.   Matichenkov, V.V., & Ammosova, JM., (1996) Effect of amorphous silica on soil properties of a sod-podzolic soil. Eurasian Soil Science 28(10):87-99.

28.   Jacinin, N.L. (1994) Colloid High-Molecular Systems in Northern Kazahstan Solonetz, PhD Thesis Tashkent.

29.   Bennett, P.C., Rogers, J.R., Hiebert, F.K., Choi,W.J. (2001) Silicates, silicate weathering, and microbial ecology. Geomicrobiol. J. 18, 3 –19.

30.   Harley, A.D., (2002): The evaluation and improvement of silicate mineral fertilisers, PhD Thesis University of Western Australia.

31.   Rogers, J.R. & Bennett, P. (2004) Mineral stimulation of subsurface microorganisms: release of limiting nutrients from silicates, Chem Geol 203, 91–108.

32.   Harley, A. & Storer, P.(2004) Silicate minerals: increased microbial stimulation, source of nutrients & de-facto organic matter? Implications for mine rehabilitation, In press.

33.   Malinovskaya, I.M., Kosenko, L.V., Votselko, S.K., Podgorskii, V.S., (1990). Role of Bacillus mucilaginosus polysaccharide in degradation of silicate minerals. Mikrobiologiya 59, 49–55.

34.   Berthelin, J., (1988). Weathering microbial processes in natural weathering. In: Lerman, A., Meybeck, M. (Eds.), Physical and Chemical Weathering in Geochemical Cycles. Kluwer Academic, New York, pp. 33– 59.

35.   Bolan NS (1991) A critical review on the role of mycorrhizal fungi in the uptake of phosphorus by plants. Plant Soil 134: 189-207.

36.   Smith SE, Read DJ (1997) Mycorrhizal Symbiosis. Academic Press, San Diego, CA.

37.   van Hees, P. A. W., Jones, D. L., Jentschke, G. & Godbold, D. L. (2004) Mobilization of aluminium, iron and silicon by Picea abies and ectomycorrhizas in a forest soil. European Journal of Soil Science 55 (1), 101-112.

38.   Lumsdon D.G., & V.C Farmer (1995) Solubility characteristics of proto-imogolite sols: how silicic acid can detoxify aluminium solutions. European Soil Sci., 46, 179-186