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Presentasi berjudul: "PENTINGNYA SILIKAT BAGI TANAH DAN TANAMAN TEBU"— Transcript presentasi:

Bahan kajian MK Pupuk dan Pemupukan Diabstraksikan oleh Prof Dr Ir Soemarno MS Jur Tanah FP UB Oktober 2011 Sumber: dirujuk dari beragam sumber referensi ilmiah, selengkapnya pelajari artikel aslinya 1

Aplikasi Si dilakukan dengan dosis 0, 55, 110 dan 165 kg ha-1 Si, bahan yang dipakai Ca-Mg silicate (262,1 g kg-1 Ca; 56,8 g kg-1 Mg; 108,4 g kg-1 Si), diaplikasikan dalam larikan pada saat tanam. Hasil tanaman terbaik dicapai pada dosis 103,2 kg ha-1 Si (952 kg ha-1 silicate). Aplikasi silikat meningkatkan kandungan Si-tersedia dalam tanah, yaitu ekstraksi 0.5 mol L-1acetic acid dan 0.01 mol L-1 CaCl2. Konsentrasi Si dalam daun tebu ditentukan oleh kultivar nya (A =3 g kg-1; B =2.18g kg-1). Dalam batang tebu, ternyata biomasa dan seapan Si terbaik diperoleh pada aplikasi dengan dosis 89 kg ha-1 Si, tidak ada efek pada keruskaan akibat penggerek batang. Sumber: … 2

3 Rancangan Percobaan Aplikasi Si
The experiment was set up in a completely randomized factorial scheme with four silicon rates (0, 55, 110 and 165 kg ha-1 Si), two cultivars (IAC and SP ), and 4 replications. The source of silicon was Ca-Mg silicate containing g kg-1 Ca; 56.8 g kg-1 Mg; g kg-1 Si. All plots received the same Ca and Mg quantities with additions of dolomitic lime (320g kg-1 Ca, 29.5 g kg-1 Mg) and/or MgCl2 (11.9% Mg) when necessary. The cultivars were chosen based upon yield potential, precocity, good number of sprouts under sugarcane mulch residue and differences on stalk borer tolerance (Diatraea saccharalis): low tolerance (SP ; Coopersucar) and intermediate tolerance (IAC ; Landell et al., 1997). Added Si as calcium magnesium silicate increased the amounts of extractable Si in a Quartzapsament soil, as well as increasing the yield and Si uptake in stalks of cultivar SP Rates of 103 kg ha-1 Si and 89 kg ha-1 Si provided the best yield and absorption of silicon of SP , respectively, but it did not promote less stalk borer damage. Sumber: … 3

4 Pentingnya Si bagi Tebu
Silicon fertilization has been shown to improve chlorophyll and structure of leaves, reduce lodging, and minimize biotic and abiotic stress, but there is little information in Brazil, the major world sugarcane producer. Positive results have been obtained with silicon application in many countries, including Brazil (Berthelsen et al., 2002; Kingston et al., 2005; Elawad et al., 1982; Korndörfer et al., 2000; Brassioli et al., 2009). Most of these results were not exclusive from silicon because the high rates of silicate can improve pH, Ca, and Mg contents (Alcarde, 1992). The silicate fertilization applied in furrow planting could be useful to reduce the cost of this product used in rates similar to lime (>2 or 3 t ha-1) and study the direct effects of Si on sugarcane. Another beneficial advantage of silicon to sugarcane is the possibility of reducing damage of insects. Studies conducted in pots and field conditions with Si has shown positive effects to control of African stalk borer Eldana saccharina. Stalk borer (Diatraea saccharalis) is a problem in Brazil controlled by biological methods and/or resistent cultivars. Good characteristics in sugarcane such as low fiber and high sugar are generally related to stalk borer tolerance. An increase of silicon uptake in sugarcane with silicate applications could reduce the damage of ‘brazilian’ stalk borer. Sumber: … 4

5 Hubungan antara Si-tanah yang terekstraks 0
Hubungan antara Si-tanah yang terekstraks 0.5 mol L-1 acetic acid dan 0.01 mol L-1 CaCl2 ( kedalaman contoh tanah 0-25cm dan cm) dengan serapan Si batang tebu dengan dosis Ca-Mg silicate. Sumber: … 5

6 Sumber: Bragantia vol.69 no.4 Campinas Dec. 2010
Si PADA DAUN TEBU The variability of silicon absorption in sugarcane cultivars can be associate with its yield and sugarcane borer (D. saccharalis) incidence. The objective of this work was to evaluate silicon uptake by the leaves and accumulation in total aerial plant and its relationship to yield, quality and stalk borer in sugarcane cultivars. Yields were superior to 100 t ha-1 at 16 months of age and IAC and RB cultivars showed the highest diameter and height, respectively. The IAC showed the highest values of sugar and lowest to fiber content. Silicon content in leaves collected at 6 months showed not significant differences. The IACSP , IACSP and IAC showed the highest silicon content in the leaves at 8 months and they were superior to 10 g kg-1 Si. Higher silicon content in the leaves was found for IAC at 10, 14 and 16 months and, in bagasse, to RB at 10 and 12 months. The foliar analysis collected at 8 months and the total aerial plant, collected just before harvest, were efficient to show differences on silicon uptake among cultivars. There was no relationship among Si uptake and yield and borer stalk incidence, which was reduced with increase of fiber content . Sumber: Bragantia vol.69 no.4 Campinas Dec. 2010 6

7 Beberapa jenis tanah di perkebunan tebu telah lama sekali digunakan untuk budidaya tebu, beberapa tanah mempunyai kandungan Si-tersedia yang rendah. The objectives were to evaluate silicon availability in soils and the relationship between availability and uptake. Therefore, we assessed the dry matter yields of sugarcane cultivated in three soil types, with and without silicon fertilization. The experiment was set up in a completely randomized factorial scheme (4 x 3 x 2) with four silicon rates (0, 185, 370 and 555 kg ha-1 Si) as Ca-Mg silicate and three soils: Quartzipsamment (RQ), Rhodic Hapludox (LV) and Rhodic Acrudox (LVdf), in four repetitions. All plots (100 L) received same Ca and Mg quantities with additions of dolomitic lime and or MgCl2. The LVdf soil showed the higher soluble silicon concentration, followed by LV and RQ. Added Si applied increased the amounts of soluble content in all soils but Si uptake in leaves of sugarcane were just increased to RQ and LV. However, addition of Si to the soils did not promote changes in dry matter yields and Si uptake on stalks of sugarcane. Sumber: The Proceedings of the International Plant Nutrition Colloquium XVI, Department of Plant Sciences, UC Davis, UC Davis 7

8 Si bagi Tebu Silicon is not an essential element (Epstein, 1999), but its fertilization to Si accumulating plants, such as sugarcane, could exhibit increased yields (Fox et al., 1967, Elawad et al.,1992; Anderson et al.,1991; Korndörfer et al., 2002). Soils cultivated with sugarcane were classified in four groups (Berthelsen et al.2002) as a function of the amount of soluble Si in CaCl Mol L-1 (mg kg-1 Si): very low (0-5), low (5-10), limited (10-20), and sufficient (20 to >50). Several classes of soils in Brazil are classified as low silicon content (Korndörfer et al., 2002) and these soils are cultivated with sugarcane. Sumber: … 8

9 Concentration uptake in leaves and stalks after harvest of sugarcane and soluble silicon in soils with silicon (*p<0.05). (Sumber: Silicon absorption by sugarcane: effect of soils type and silicate fertilization. The Proceedings of the International Plant Nutrition Colloquium XVI, Department of Plant Sciences, UC Davis, UC Davis Sumber: … 9

APLIKASI Si: EFEK FISIK DAN FISIOLOGIS Silicon is an integral part of cell walls, and has a similar role to lignin, in that it provides compression-resistance and rigidity in cell walls, thus providing structural strength to the plant. An ample supply of Si has been reported to reduce lodging (drooping, leaning or becoming prostrate) in grass crops due to improved mechanical strength. The improved rigidity of the cell walls also promotes a more erect habit and disposition of the leaves, resulting in better light interception and photosynthetic efficiency. Sugarcane cultivars high in Si may also show enhanced sucrose synthesis, due to improved photosynthesis, as shoots are not as likely to become prostrate following wind and rain. Sumber: Sugar Research and Development Corporation Final Report . SRDC Project CLW009 . CSIRO 2003 10

11 Varieties have changed substantially between 1970 and 1990, and lodging, once a factor selected against, is now considered a less important selection criterion, with the use of mechanical chopper harvesters. Consequently, plant-breeding programmes may have been inadvertently selecting varieties with lower concentrations of Si in the stalk. As there is evidence that lodging can result in loss of cane yield and reduction in sugar content, this highlights the possibility that low plant and soil Si levels may be a causal factor in declining sugarcane yields observed over recent years. Adequate Si nutrition may also assist crops withstand the effects of drought conditions in areas reliant on rainfall, or declining water quality in irrigation areas. Plants with a well-thickened layer of Si associated with the cellulose in cell walls of epidermal cells have been observed to be less prone to wilting and have improved drought resistance. Silicon may also reduced stress to salt in a similar way that it alleviates water stress. Work with cereal crops suggest that Si can both increase photosynthesis and decrease the permeability of plasma membranes of leaves of salt-stressed plants. In addition, Si has been shown to inhibit the uptake of Na and increase the uptake of K, thus alleviating the effect of salt toxicity and improving vegetative growth. Sumber: … 11

12 Ketahanan thd Stress Biotik
Improved resistance to disease and pathogenic fungal attack, due to Si applications, has been reported for a number of crops. It is generally agreed that as most parasitic fungi penetrate the host by boring through the epidermal cell wall, Si in these walls may act as a mechanical barrier. In addition, Si may also protect the plant by its association with the cell wall constituents, minimizing the enzymatic degradation that accompanies the penetration of the cell wall by the fungal hyphae. The highly silicified leaves of grasses can not only make the plant more resistant to attack by pathogenic fungi, but also to attack by predaceous chewing insects, as they can suffer a high mortality when their mandibles and maxillae become worn down, rendering their mouthparts ineffective. It is relevant, therefore, that recent history of yield decline in sugarcane dates back to the recognition of ‘Northern Poor Root Syndrome’ (NPRS) as a problem in sugarcane on Queensland’s wet tropical coast (Egan et al., 1984). Although, it has been suggested that the build-up and susceptibility to root pathogens may be the ultimate expression of other factors being out of balance in the farming system, it is plausible that low soil and plant Si levels have allowed increased susceptibility to pathogen attack. Sumber: … 12

13 Ketahanan thd stress Abiotik
Adequate Si nutrition is reported to have a major effect on the absorption and translocation of some macronutrient and micronutrient elements, assist in the negative effects resulting from nutrient imbalances, and also have the ability to alleviate, or in some cases to eliminate, the adverse effects of heavy metals, excess phosphorus and salinity. Current sugarcane production systems often apply nitrogen at rates far in excess of what may be considered necessary for maximum yield, and with high soil concentrations of phosphorus, may result in unbalanced nutrient supply on many sugarcane soils. That yield decline can be temporarily reversed by increasing N fertilizer rates to soil Si-depleted systems. However, for sustained yields, Si fertilisation is required to balance applied nutrients, particularly N, when high rates can result in increased problems with lodging. Although Si additions are reported to improve P nutrition, conversely, continued use of superphosphate may have also resulted in accelerated depletion of soil Si reserves, since P effectively competes with Si for specific sorption sites, thereby resulting in the loss of Si through leaching. 13

14 Soil Si status, indicative of potential soil productivity
Si dalam Tanah Soil Si status, indicative of potential soil productivity Silicon is recognized as a major constituent of soils. It is present in the solid phase of soils as alumino-silicate clay minerals and crystalline minerals, and also in a number of amorphous forms such as plant phytoliths. In the soil solution, or liquid phase, Si is present as mono- and poly-silicic acids, and also present as complexes with inorganic and organic compounds. While it is the mono-silicic acid component that is taken up by plants and has a direct influence on crop growth, the poly-silicic acids, and probably the inorganic and organic Si complexes, are important as sources/sinks of Si which can replenish the soil solution following crop use, but importantly, they can have a significant effect on soil properties such as improving soil aggregation and increasing soil water holding capacity and also increasing the exchange and buffering capacity of soils. It has also been suggested that the organosilicic compounds play a specific role in organic matter formation. Sumber: … 14

15 Reaksi-reaksi Si dalam tanah
Sumber: … 15

16 Ketersediaan Si dalam tanah
In general, most soils have appreciable amount of be adequate for crop growth. Although quartz is a major source of Si in many soils, the rate of dissolution of this mineral is very slow and therefore does not contribute significantly to the labile pool of soluble Si. For plant growth the important forms of soil Si are the soluble forms, mainly monosilicic acid (Si(OH)4), various polymers and silica gels, Si adsorbed onto sesquioxidic surfaces, and that present in crystalline and amorphous soil minerals. The quantity present in each of these forms is largely controlled by the dominant soil mineral and the amount of Si lost (desilication) through weathering. The solubility of Si in the soil is influenced by several factors including, particle size, soil pH, organic complexes, the presence of aluminium, iron and phosphate ions, temperature, exchangeable/dissolution reactions, and soil moisture. Sumber: … 16

Aplikasi bahan silikat ke tanah yang miskin Si-larut dapat meningkatkan hasil tebu dan hasil gula , sedangkan respon pertumbuhan tebu ditunjukkan dengan indikator tinggi tanaman dan bobot batang, diameter batang dan jumlah batang. METODE APLIKASI Si Aplikasi kalsium-silikat pada pertanaman tebu dapat dilakukan dengan cara disebar dan kebudian dibenamkan ke tanah sebelum penanaman bibit. Sumber: … 17

18 Manfaat aplikasi pupuk silikat pada tanaman tebu:
Menetralisir kemasaman tanah: Ini akan memperbaiki aktivitas mikroba tanah dan ketersediaan N,P, S dari bahan organik tanah; mereduksi toksisitas Fe, Al, Mn dalam larutan tanah Mensuplai unsur hara Ca, Si, P, K, Mg,S dan unsur mikro Meningkatkan hasil tebu dan hasil gula: diameter dan panjang batang, jumlah batang, daun-hijau, ineks pertumbuhan Memperbaiki fotosintesis dan produksi klorofil Regulator ensim dalam sintesis gula, dan simpanan sukrose dalam tanaman Mereduksi kerobohan tanaman, habit tumbuh tegak, sehingga efisien cahaya Meningkatkan ketahanan tanaman terhadap gangguan hama dan penyakit Mereduksi transpirasi sehingga air lebih efisien Mereduksi toksisitas Mn dan mencegah akumulasi Mn di daun Memperbaiki nutrisi P: Mereduksi fiksasi P, meningkatkan kelarutan P-tanah, efisiensi pemanfaatanP oleh tanaman Memperbaiki kesuburan tanaman Sumber: … 18

19 Pangaruh dosis aplikasi Ca-silicate terhadap tinggi batang dan jumlah batang tebu
Sumber: … 19

20 Pengaruh aplikasi Ca-silikat terhadap Konsentrasi Si (%) dalam daun muda yang telah mekar sempurna (TVD) pada tanaman umur 7 bulan; hasil batang tebu, ccs dan bobot segar umur 8 bulan setelah tanam; dan hasil akhir tebu, ccs dan hasil gula 20

21 Pengaruh aplikasi Ca-silikat terhadap kadar serat (%) batang tebu, persen daun yang terinfeksi penyakit karat-orange dan becak kuning pada umur 8 bulan setelah tanam Sumber: … 21

22 Pengaruh aplikasi Ca-silikat terhadap hasil tebu ratoon pertama, ratoon ke dua, tebu tanaman, dan kumulatifnya Sumber: … 22

23 Hubungan antara hasil relatif tebu dengan indeks ketersediaan Si-tanah
(a) Si(sol) ekstraksi 0.01 M CaCl2 (b) Si(ext) ekstraksi M H2SO4. Sumber: … 23

24 (a) Si(sol) dari ekstraksi 0.01 M CaCl2
Hubungan antara hasil relatif tebu dengan indeks ketersediaan Si-tanah (AEC / 100g clay) pada dua jenis tanah yang berbeda (a) Si(sol) dari ekstraksi 0.01 M CaCl2 (b) Si(ext) dari ekstraksi M H2SO4. Sumber: … 24

25 Pengaruh aplikasi calcium silicate terhadap tingkat hijauanya daun (SPAD units), tebu ratoon pertama dan ke dua. Sumber: … 25

26 Pengaruh aplikasi bahan silikat terhadap tingkat hijaunya daun (SPAD units) pada tanaman tebu
Sumber: … 26

27 Reaksi-reaksi yang terjadi dalam tanah setelah aplikasi calcium silicate slag (Kato and Owa, 1997a).
Sumber: … 27

28 Karena calcium silicate reaksinya lambat untuk menghasilkan asam mono-silikat (H4SiO4) yang tersedia bagi tanaman (reaksi 1 - 4), Ca2+ dan Ca(OH)2 hasil dari reaksi akan diserap pada koloid tanah (reaksi 5 dan 6). Permukaan hidroksilasi pada permukaan tanah akan melepaskan proton, secara bertahap akan mengasamkan tanah. Kalau pH tanah menurun maka kelarutan Si dari terak kalsium silikat akan meningkat. Sumber: … 28

29 Reaksi kondensasi dan pengendapan polimer Si (Drees et al., 1989)
Sumber: … 29

30 Flokulasi Si-polymorphs dengan pembentukan ion-ion hidroksida logam yang bermuatan positif (MOH+) (Drees et al., 1989). Sumber: … 30

31 Pengaruh aplikasi Ca-silikat terhadap KTK tanah permukaan 0-10cm, diukur setelah tanaman tebu (2000) dan setelah ratoon pertama (2001). Sumber: … 31

32 Hubungan antara hasil tebu (ton/ha) ratoon pertama dengan kadar Si (%) daun muda (TVD) tanaman tebu umur 7 bulan. Sumber: … 32

33 Si Memperbaiki Produksi Tebu
Tebu sangat respons terhadap aplikasi bahan-bahan sumber silika. Aplikasi bahan-bahan silikat dengan dosis 0, 5, 10, 15, dan 20 metric tons/ha, brupa bahan-bahan TVA slag, Florida slag, dan Portland cement. Bahan-bahan silikat disebar di permukaan tanah dan dicampur rata dengan tanah menggunakan bajak “disc harrow”. Aplikasi silikat meningkatkan tinggi tanaman, diameter batang, jumlah batang, hasil tebu dan hasil gula, baik pada tanaman tebu maupun ratoonnya. Aplikasi bahan silikat sebanyak 15 metric tons/ha meningkatkan hasil tebu dan hasil gula masing-masing 68 dan 79% untuk tebu tanaman; sebesar 125 dan 129% pada tebu ratoon. Peranan vital Si dalam pertumbuhan tanaman tebu terbukti dengan meningkatnya ukuran tanaman dan jumlah anakan akibat aplikasi bahan silikat. Sumber: Agronomy Journal Vol. 74 No. 3, p.  33

34 PENTINGNYA Si BAGI TEBU Sumber: J. Plant Nutr. 22 (12):1853-1903. 1999
Silicon (Si) is one of the most abundant elements found in the earth's crust, but is mostly inert and only slightly soluble. Agriculture activity tends to remove large quantities of Si from soil. Sugarcane is known to absorb more Si than any other mineral nutrient, accumulating approximately 380 kg ha-1 of Si, in a 12-month old crop. Sugarcane (plant growth and development) responses to silicon fertilization have been documented in some areas of the world, and applications on commercial fields are routine in certain areas. The reason for this plant response or yield increase is not fully understood, but several mechanisms have been proposed. Some studies indicate that sugarcane yield responses to silicon may be associated with induced resistance to biotic and abiotic stresses, such as disease and pest resistance, Al, Mn and Fe toxicity alleviation, increased P availability, reduced lodging, improved leaf and stalk erectness, freeze resistance, and improvement in plant water economy. Sumber: J. Plant Nutr. 22 (12): 34

35 Fungsi Si dalam tanaman tebu adalah:
FUNGSI Si BAGI TANAMAN Tanaman tebu mengakumulasikan sejumlah besar Si dalam bentuk silica gel (SiO2.nH2O) yang dilokalisir dalam tipe-tipe sel tertentu. Fungsi Si dalam tanaman tebu adalah: Memperkuat dinding sel (ketahanan terhadap lodging); Ketahanan terhadap hama dan penyakit; Reduksi evapotranspirasi; Reduksi toksisitas logam berat Unsur esensial bagi pertumbuhan tanaman normal. PEMUPUKAN Si Kajian-kajian tentang hara Si pada tanaman tebu telah banyak dilaporkan di Australia, South Africa, Brazil, Taiwan, India, Mauritius, Puerto Rico, the United States dan negara-negara lain produsen tebu. Pemupukan Si juga telah dipraktekkan untuk memperbaiki produktivitas tebu di berbagai perkebunan tebu di dunia. Efisiensi pemupukan Si ternyata sangat ditentukan oleh karakteristik fisika dan kimia bahan pupuk-silikat ; teknologi aplikasinya, waktu aplikasinya dan dosis aplikasinya. 35

Sugarcane absorbs large amounts of Si from soil. According to Samuels (1969), at 12-months the above ground parts contained 379 kg ha-1 of Si, compared with 362 kg ha-1 of K and 140 kg ha-1 of N. Ross et al. (1974) reported the removal of 408 kg ha-1 of total Si from soil by a sugarcane crop (tops + millable cane) yielding of 74 t ha-1. The removal of Si from soil could be more important in intensively cultivated areas. As a result of the Si export of this magnitude, a temporary depletion of bio-available Si in soils could also be a possible factor of declining yields of ratoon crops. In other words, there may be an apparent need for consideration of Si nutrient management in developing appropriate integrated nutrient management system for sustainable sugarcane production, especially in certain ecoregions having Si deficient weathered soils and organic soils. Sumber: … 36

There is ample evidence that different species uptake greatly different amounts of Si. Legumes and other dicotyledons have much lower levels than monocotyledons, for example, the Gramineae. Sugarcane is a Si accumulator plant, which strongly responds to Si supply. The Si form that which sugarcane usually absorbs has no electric charge (H4SiO4) and is not very mobile in the plant. Because the uptake of undissociated H4SiO4 may be nonselective and energetically passive, and its transport from root to shoot is in the transpiration stream in the xylem, the assumption has sometimes been made that the movement of Si follows that of water (Jones and Handreck, 1965). The silicic acid is deposited mainly in the walls of epidermal cells, where it is integrated firmly into the structural matter and contributes substantially to the strength of the stem. The distribution of Si within the shoot and shoot parts is determined by the transpiration rate of the part (Jones and Handreck, 1967). Most of the Si remains in the apoplasm mainly in the outer walls of the epidermal cells on both surfaces of the leaves as well as in the inflorescence bracts of graminaceous species and is deposited after water evaporation at the end of the transpiration stream, (Hodson and Sangster, 1989). Silicon is deposited either as amorphous b (SiO2. hH2O, 'opal') or as socalled opal phytoliths with distinct threedimensional shapes (Parry and Smithson, 1964). The preferential deposition of Si in the apoplasm of epidermal cells and trichomes is reflected in similarities between surface features of leaf and structure of Si deposits (Lanning and Eleuterius, 1989). The epidermal cell walls are impregnated with a firm layer of Si and become effective barriers against both fungal infections and water loss by cuticular transpiration. Despite that, there is increasing evidence for the necessity to modify the traditional view of Si deposition in the cell walls as a purely physical process leading to mechanical stabilization (rigidity) of the tissue and acting as a mechanical barrier to pathogens. Silicon may be involved in cell elongation and/or cell division. In a field study, plant crop height was quadratically related to the rate of Si applied, while plant crop stem diameter was linearly related (Elawad et al., 1982a). Gascho (1978) reported that application of TVA slag and Na silicate to greenhouse grown sugarcane increased plant height. Phicket (1971) indicated that some of the effects of Si on sugarcane were longer stalks with larger diameters and increased number of suckers. These observations on cane and observations for other crops suggest a possible role of Si in cell elongation and/or cell division (Elawad et al., 1982ab). Ayres (1966) determined that only 15% of the total plant Si are present in sugarcane stalks at 14 months. The leaf sheaths on the best cane-growing soils contained about 2.5 percent Si. Using the sixth leaf sheath, Halais (1967) suggested critical levels of 1.25 percent of Si and 125 mg dm-3 of Mn. If the Si level was below this value, Si responses could be expected. Under field conditions, in Florida, Anderson (1991) suggested that at least 1% Si (~2.1 % SiO2 in the leaf dry matter) is required for optimal cane yield. At 0.25% Si the yield drops to about 50%. According to Rodrigues (1997), increasing Si rate from 0 to 924 kg ha-1 using Wollastonite, resulted in substantial increase of the Si content in the leaves from 0.7 to 1.93 % and Si in the soil from 14 to 46 mg dm-3 (TABLE 2). Better Si-accumulating cultivars may have the advantage of requiring lower rates of Si fertilizer or less frequent applications. A relatively narrow base of sugarcane germplasm demonstrated significant variability for Si content in leaf tissue (Deren et al., 1993). Korndörfer et al. (1998a) also found that sugarcane cultivars have different capacities to accumulate Si in the leaves. The Si levels in the leaf were of 0.76, 1.04 and 1.14% respectively for the cultivars: RB72454, SP and SP71- 6163. 37

Research work demonstrating the use of silicate slag as a source of Si for sugarcane has been largely conducted in Hawaii, Mauritius, and Florida. Yield responses are great enough that sugarcane grown in the Everglades (South Florida) is routinely fertilized with calcium silicate when soil tests indicate the need. However, Si fertilization requires large quantities of slag (generally 5 Mg ha-1), making it quite costly (Alvarez et al., 1988). Yields of cane and sugar in Hawaii have been increased 10-50% on soils low in Si, and many sugar plantations regularly apply calcium silicate in responsive fields (Ayres, 1966; Clements, 1965a; Fox et al., 1967b). Increased yields of sugarcane in fields have been reported in Mauritius (Ross, 1974) and Puerto Rico (Samuels, 1969); while in South Africa (Preez, 1970) and Brazil (Gascho and Korndörfer, 1998), several sources of silicate increased sugarcane yields in pots. 38

In sugarcane, small rust-colored or brownish spots on the leaves of cane growing on highly weathered soils characterize a leaf disorder called freckling. In severe cases, affected lower leaves may die prematurely and can affect cane yield. Freckled plants are less efficient in performing photosynthesis not only because they have less leaf but also because many leaves are freckled. This leaf disorder was corrected by application of silicate materials (Clements, 1965b). Ayres (1966), Fox et al. (1967b), and Wong You Cheong et al. (1972) have also noticed that leaf freckling symptoms in sugarcane were gone following Si treatments. Elawad et al. (1982a) observed significant decrease in percent freckling in the plant crop as well as the ratoon crop with application of 20 t ha-1 of TVA slag to muck soil. The mechanism for the disappearance of leaf freckling in sugarcane following Si application is still not well understood. Clements et al. (1974) attributed leaf freckling mainly to the presence of toxic levels of Fe, Al, Mn and Zn in the soil solution. However, Gascho (1978) stated that the development of freckled leaves is an expression of the plant's need for Si. Silicon deposited in the epidermal tissue mechanically deters hyphae invasion (Takahashi, 1996). Furthermore, Si physiologically promotes ammonium assimilation and restrains the increase in soluble nitrogen compounds, including amino acids and amide, which are instrumental for the propagation of hyphae (Takahashi, 1996). Recently, Raid et al. (1992) investigated the influence of cultivar and soil amendment with calcium silicate slag on foliar disease development in sugarcane hybrids (TABLE 6). Severity of sugarcane rust (Puccinia melanocephala H. Syd. and P. Syd) was not affected by application of silicate slag. However, they noticed significant reduction in severity of ringspot with the addition of the slag (Leptosphaeria sacchari Breda de Hann) by an average of 67% across the five cultivars studied. Silicon is known to be deposited at the external surface of cell walls of plants, thus forming a mechanical barrier to penetration of the pathogen causing ringspot but not to that of rust in sugarcane (Kunoh, 1990; Raid et al., 1992). A hypothesis has been presented that the polymerized Si acids fill up apertures of cellulose micelle constituting cell walls and make up a Si cellulose membrane. This membrane is supposed to be mainly responsible for protecting the plant from some diseases and insects (Yoshida et al., 1969) 39

While studying the influence of UVB radiation and soluble Si on growth of sugarcane, Elawad et al. (1985) additionally observed increased resistance of sugarcane to stem borer (Diatraea saccharalis F.) with improved Si nutrition. Newly hatched D. saccharalis larvae, when starting their attacks on sugarcane plants, do so by feeding on epidermal tissue of the sheath, leaves and developing internodes in the immature top of the plants. The presence of Si crystals in these tissues should hinder the feeding of the insect, which in this phase has rather fragile mandibles. Plants like sugarcane and rice, with high Si contents, seem to interfere in the feeding of larvae, damaging their mandibles. It is possible that plants with higher Si contents in their tissue would have a higher level of resistance to the infections by such pests. The high Si levels in Na2SiO3 treated plants may have served as a deterrent to the borers. A significant negative relation was observed between leaf Si content and shoot borer incidence. Sugarcane varieties with a higher number of Si cells per unit area in the leaf sheath portion 5 to 7 cm from the base were found resistant to the shoot borer. The percentage of the incidence of borer damage was less in sugarcane (var. GPB 5) treated with bagasse furnace ash and silicate slag than in untreated sugarcane. It is interesting to note that increased application of N fertilizers alone increased the incidence of sugarcane stalk borer, and that of another borer (Chilo auricilius Dudgeon) in India. The increase of the borer’s incidence may be partly due to the formation of softer stalks resulting from the lower than adequate levels of plant Si required for strengthening of the stalk cells. In other words, the borer incidence could have been prevented by application of Si together with N fertilizers. 40

Water stress under field conditions is common and affects cane yields. Improved Si nutrition may reduce excessive leaf transpiration. One of the symptoms associated with Si deficiency is the excessive rate of transpiration. The rate of transpiration of Si deficient plants increased by about 30% over the rate of control plants (rates were measured as grams of water lost through transpiration per gram of dry weight per day). Okuda and Takahashi (1965) obtained a similar result, but found that in barley the effect was small (less than a 10% difference between Sideficient and control plants). This observation suggests a role for Si in the water economy of the plant. An increased rate of transpiration in Si-deficient plants could explain the wilting that may occur, particularly under conditions of low humidity, and could also help to explain the increased accumulation of Mn and other mineral nutrients in the aerial parts of Si deficient plants. The rate of transpiration is presumably influenced by the amount of silica gel associated with the cellulose in the cell walls of epidermal cells. Hence, a well thickened layer of silica gel should help to retard water loss, while epidermal cell wall with less silica gel will allow water to escape at an accelerated rate. Since this role of Si nutrition may result in water economy and may be important in water management, field research on this potential beneficial has merit. 41

One other effect of increased plant Si content, which has been reported in literature, is the increased mechanical strength of plant tissue, which results in reduced lodging. Under field conditions, particularly in dense stands of sugarcane, Si can stimulate growth and yield by decreasing mutual shading by improving leaf erectness, which decreases susceptibility to lodging. Leaf erectness is an important factor affecting light interception in dense plant population and, hence, photosynthesis. In rice, Si supply increased the photo-assimilation of carbon, especially after heading, and promoted the translocation of assimilated carbon to the leaves. This effect of Si on leaf erectness is mainly a function of the Si depositions in the epidermal layers of the leaf panicle. 42

43 INVERSI SUKROSE Few investigations of the role of Si in sugarcane have considered the mechanism by which it affects sugarcane tonnage production. However, Alexander et al. (1971) has undertaken the task of finding the role that Si plays in the synthesis, storage and retention of sucrose in the sugarcane plant. He found that sucrose inversion in sugarcane juice samples was delayed for several days by adding sodium metasilicate immediately after milling. Chromatographic evidence suggests that at low levels metasilicate forms a physical complex with sucrose which prevents the union of invertase with its substrate. The hypothetical fructose-silicate configuration is retained even after sucrose is inverted, thereby preventing fructose from being metabolized by microorganisms. Fructose appears to be the preferential hexose for microbial growth, i.e. most suitable carbon source. The effective preservation of fructose by silicates may constitute a bacterial repression operating in addition to the invertase-inhibitory action. Next to K, Si is the most extensive constituent of ash in sugarcane juice. It is the highest component of millable stalks ash and represents an even greater percentage in leaves. However, silicates in cane are believed to be one of the major contributors to mill roll wear. 43

44 For research purposes, many different Si sources have been tested:
BAHAN SUMBER SILIKAT The usual carrier for Si is calcium silicate and this material can also supply Ca to a Ca-deficient soil. The Hawaiian Cement Corp. first manufactured calcium silicate in August 1965. Gascho and Korndörfer (1998) working with four different soils groups from Brazil and several Si sources (Wollastonite, thermal-phosphate, calcium silicate and basic slag) concluded that thermal-phosphate was the most effective source to supply both Si and P to the rice plant. In several studies, no attempt was made to maintain constant Ca levels with increasing calcium silicate applications. It is important to separate Si from Ca effects. Ayres (1966) reasoned that since both calcium silicate and calcium carbonate treatments had increased yields, the calcium supply probably was not the factor causing higher yields in their studies. Teranishi (1968) concluded that yield increases from calcium silicate applications could not be attributed to Ca supply in his experiment since plant Ca was above the critical level for sugarcane and also since calcium carbonate had been added to the zero Si plots to maintain pH and supply adequate Ca. According to Ross et al. (1974), calcium silicate applied to low Si soils at planting increase annual cane yield over a 6 year cycle (TABLE 4) and well demonstrated the residual effect from this source. For research purposes, many different Si sources have been tested: Wollastonite (CaSiO3), cement kiln fired (fused) calcium silicate, Portland cement (9 to 23 % Si), di-calcium ortho-silicate (Ca2SiO4), calcium metasilicate, minigranulated calcium metasilicate, electric furnace slag (by-product of furnace production of elemental P), blast furnace slag, basic slag, Thomas slag, mill furnace ashes, crushed basalt, volcanic cinder, and others (Rozeff, 1992abc) (TABLE 9) 44

45 KALSIUM METASILIKAT Calcium metasilicate was generally much more soluble and readily available to sugarcane than calcium ortho-silicate. Mini-granules of calcium metasilicate, which were small, spherical (50 to 150 mesh) made from fine (100 to 200 mesh) material using 2% sodium oxide as a binder, were agronomically equivalent to fine ungranulated calcium metasilicate (HSPA, 1982). A fine grade of Si fertilizer was best for increasing Si content and grain yield. Rice yields increased relative to the control by 20-26%, 18%, and 4-11% for the fine, standard, and pelletized forms, respectively in 1990/1991. Agronomic feasibility of mini-granulation of CaSiO3 has been confirmed. When containing high amounts of Si, both granular and powered slag are equally efficient. These are useful findings because they offer potential the option of mini-granulation of fine silicate sources for solving their handling problem. 45

46 Rekomendasi lainnya adalah 4.94 t ha-1 calcium metasilicate (CaSiO3).
DOSIS APLIKASI SILIKAT Dosis aplikasi Si sangat dipengaruhi oleh komposisi kimiawi dari sumber Si, kandungan Si-tersedia dalam tanah, dan kandungan Si dalam tanaman. Rekomendasi aplikasi silikat tanaman tebu di Hawaii 7.5 tons ha-1 bahan terak TVA (Tennessee Valley Authority). Rekomendasi lainnya adalah 4.94 t ha-1 calcium metasilicate (CaSiO3). Rekomendasi untuk tebu ratoon t ha-1 CaSiO3, kalau kandungsn Si dalam tanah kg ha-1. Sumber: … 46

Umumnya aplikasi Si dilakukan ke tanah sebelum penanaman bibit. Pengalaman petani tebu di Florida, kalau respon terhadap bahan Si dapat diperoleh pada aplikasi tahun pertama, maka tidak perlu aplikasi Si lagi paling tidak selama empat tahun. Dalam sistem rotasi / pergiliran tanaman padi dengan tebu, aplikasi terak-silikat sebelum tanaman tebu , dan sebelum tanaman padi dalam rotasinya dengan tebu, menunjukkan respon agronomis yang bagus. Pengalaman menunjukkan bahwa aplikasi terak-silikat yang lebih menguntungkan adalah sebelum tanaman padi dalam sistem rotasi padi – tebu. Sumber: … 47

The particle size of the Si fertilizer is important in increasing Si content of leaves and subsequent disease control. Particle size is associated with increased surface area; consequently, the distribution and dissolution of smaller Si particles mixed in the soil is enhanced and the probability of root particle contact is increased. Combining fine particles into pellets probably results in less Si-soil contact, leading to reduce Si availability to the crop, although some particle degradation could occur during soil incorporation. The particle should be of a size and well mixed with the soil. If very fine, Si sources create dusty conditions and can adversely affect material handling and application performance in the field. Special precautions are necessary for avoiding exposure of workers to the dust. This dust problem may limit the use of silicate slag for sugarcane in developing countries where it will be mainly applied manually. Mini-granulation of fine calcium silicate materials seems to a potential alternative for addressing the dust problem. Small particle size increases the effectiveness of silicate materials. Harada (1965) called attention to the superiority of finely ground TVA slag compared with coarsely ground, 16 mesh (<1.6 mm) material. Sumber: … 48


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