Potential Applications of Silicate Solubilizing Bacteria and Potassium Silicate on Sugarcane Crop under Drought Condition

The decline of soil nutrient status and productivity of crops, and restoration of soil health is a key global concern. Crop yields are reduced by soil degradation, which endangers the world's food supply. Crop yields and soil health are further decreased by improper fertilizers use in conjunction with intense cropping. A wide variety of plants, particularly monocotyledonous crops can collect significant levels of silicon in their organs showing the benefits of silicon in terms of growth, biomass, and yield, whereas most dicots are unable to accumulate enough Si under their epidermal system. In the present investigation, treatment of applying silica solubilizer at a rate of 12.5 kg with 50 kg FYM/ha in soil with sett treatment of 0.5% K2SiO3,2.5% urea and potash foliar spray in a specified time showed a significant result in all the growth and yield parameters tested when plant and its ratoon were in drought condition.


Introduction
The second most prevalent element, silicon (Si), is typically found in silicates (SiO 3 ) of Al, Mg, Ca, Na, K, or Fe, which are usually unavailable to crops.The chemical and biological reactions of Si in soil often determine how easily they can reach the plant roots.Through a variety of methods, plants can absorb silicon (Si) as soluble mono-silicic acid, which strengthens the cell wall [1,2].Numerous plant species, including Cucumber, rice, oats, barley, wheat, and sugarcane, are known to be more resistant to disease, insect attack, and unfavorable climatic conditions when their cell walls are fortified with silicon [3][4][5][6].
The sugarcane (Saccharum spp.), according to extensive research, is capable of removing up to 470 and 700 kg of silica per year from silica-rich soils [7].According to [8] these cereal plants absorb >1.0% of the dry Si content of the shoot.On the weathered tropical or subtropical soils such as Oxisols, Ultisols, and organic histosols on which rice and sugarcane are typically grown have often lost their soluble Si sources due to high temperatures and rainfall [9].These highly weathered soils lack essential nutrients and are acidic, which may cause them to be rich in soluble forms of aluminum (Al) when the soil pH is 5.5 [10].As a result, soluble Si can be removed from the soil by a reaction that creates insoluble hydroxyl aluminosilicates (HASs) [11,12].However, yield responses have been frequently reported after additions of Si to soil (9).
Climate changes such as extreme weather and unexpected temperature fluctuations have reduced crop productivity [13][14][15].Therefore, soil fertility management is critical to crop production as it contributes to greater and long-lasting crop yields.Nutrient management and monitoring are fundamental for optimal crop production.Sugarcane provides significant yields with a regular supply of nitrogen (N), phosphorus (P), and potassium (K), as well as other macro and micronutrients.According to Shen et al. [16] Si application markedly increased the sugarcane fresh weight and Si, P, and K contents in leaves.Though the role of Si in physiological and morphological involvement in growth has revealed it is still rarely considered as a nutrient for long-term sugarcane cultivation.
According to [17,18], microorganisms are recognized to have a significant role in the dissolution and uptake of minerals such as silicates and phosphates resulting in improved plant growth under various stress circumstances [18,19].It is well known that microbe-produced organic acid dissolves both insoluble silicon and phosphate, increasing their availability to plants [20].According to several studies, bacteria solubilize silicates to enhance the availability of its plants [21].
Silicon is made available to plants by microorganisms and chemical reactions in the soil [22].The efficiency of silicon leads to enhanced photosynthesis and brix content, heightened resistance to diseases and insects, and reduced instances of sunburn, withering, and post-harvest decline [23].Biofertilizers, regarded as ecologically benign and economical alternatives to chemical fertilizers constitute a crucial element of integrated nutrient management [24,25].Silicate solubilizing bacteria (SSB) are capable of solubilizing phosphates, potassium, and insoluble forms of silicates, thereby enhancing soil fertility and plant productivity [26,27].Numerous studies have demonstrated that Silica Solubilizing Bacteria have positive effects on crop development, photosynthesis, and nutrient absorption from the soil [28].
Drought stands out as a prominent abiotic factor with detrimental effects on crop growth and global production [29].The application of potassium silicate directly onto leaves has been shown to enhance leaf erectness, boost photosynthetic efficiency, and mitigate lodging in sugarcane [30,31].Through the regulation of plant water potential, photosynthetic activity, stomatal conductance, and leaf length, silicon diminishes the plant's susceptibility to various stresses, particularly under high transpiration rates [32,33].However, the amount of silica deposition in leaves of sugarcane grown with silicon mobilizing bacteria, along with calcium silicate and potassium silicate has never been studied before.Therefore, the objective of this study was to examine the effects of silicon on sugarcane yield contributing traits, as well as its relationship with other nutrients in leaf tissues and soil nutrients.

Location of Field Experiments
Field experiments were carried out at the Sugarcane Research Station situated in Cuddalore, Tamil Nadu, India.The geographical location is approximately 11°46'N latitude and 79°46'E longitude, with an altitude of 4.6 meters above mean sea level (MSL).The region experiences an average annual rainfall of 1210 mm.The maximum temperature recorded is 35.70°C, the minimum temperature is 25.92°C, and the relative humidity is 83.23%.The selected test variety for cultivation in the experiment was the CoC 25 clone, and it was grown in sandy loam-textured soil conditions.The initial soil sample analysis results can be found in Table 1.
(Note: Water stress was induced by withholding irrigation during a crucial period of 60-150 DAP.Irrigation scheduling was then adjusted to occur once every 15 days.)

Tiller Population
On the 100 th day following planting, tillers were counted from the net plot area and reported as the number of tillers per germinated bud (including mother shoots) or tillering capacity (per row basis).

Leaf Area
Leaf area was calculated for each plant using the leaf length, leaf breadth, and K constant value and expressed as cm 2 per plant.

Leaf Area Index (LAI)
The [34] formula was used to calculate the leaf area index.

Specific Leaf Area (SLA)
Specific leaf area was calculated by employing the following formula of [35] and expressed in cm -2 g -1 .

Specific Leaf Weight (SLW)
The following formula from [36] was used to compute the specific leaf weight and is represented in mg cm -2 .

LAI =
Leaf area per plant Ground area occupied per plant SLA = Leaf area Leaf dry weight

Cane Weight
Six canes were selected at random from each plot, cut at the base, detopped at the mature inter-node level, and weighed.The average cane weight was determined and expressed as g plant -1 .

Cane Dry Weight
Six randomly selected canes from each plot were cut at the bottom, detopped at the mature inter-node level, and their weight was measured.The canes were then preserved for drying, and their weight after drying was computed and expressed as g plant -1 .

Nutrient Uptake
For each plant, the generation of dry matter was noted at various stages.By multiplying the dry weight by the nutrient content, the amount of nutrition taken up by the plant was determined.The units are expressed as (Kg/ha).

Soil Nutritional Status
Soil samples were collected in different places and dried under shade for further nutrient analysis.Nitrogen in soil samples was analyzed by Micro kjeldhal method described by [37] and Vanado molybdate yellow colour method was adopted for Phosphorus estimation and Potassium was analyzed flame photometric method by using triacid extract described by [38].

Brix (%), Pol (%) and Purity Coefficient (%)
Six randomly chosen canes were used to analyze the juice quality parameters brix, pol, and purity during harvest.In an automatic sucrose analyzer system created by Electronic Automation of West Germany, the juice brix, sucrose percentage, and purity were measured.The juice was cleared using Horne's dry lead subacetate before being fed into the device [39].The purity coefficient was calculated as the ratio of sucrose to all solids.

Commercial Cane Sugar
According to [39] commercial cane sugar (CCS) percent was calculated as follows and expressed as a percentage.

SLW =
Leaf dry weight Leaf area Mg:Ca 1.17

Scanning Electron Microscope
Harvest-stage leaves of each sugarcane crop were divided into sections and placed in Eppendorf tubes containing a CCS (%) = 1.033 pol in juice percentage − 0.292 brix percentage in juice karnovsky fixative solution for 24 hours.The solutions were transferred promptly into a cryoprotectant solution (30% glycerol) for 30 minutes.After being chilled in liquid nitrogen, the samples were cut into small pieces using a knife on a cooled metal plate.The fragments were first dried on paper towels and put in Petri dishes with distilled water.After that, they were attached to a stub specimen container formed of a brass disc that was 12-13 mm (0.5 in diameter) and covered with aluminum foil using double-sided carbon tape.Several fragments had the abaxial leaf surface set in the up position, while the abaxial side was fixed in the down position.The stub-mounted samples were put in a Balzers SCD 050 evaporator for plating after three days.The specimen-holding stubs were initially placed in desiccators filled with silica gel .The same examination was done using a LEOEVO 40 XVP scanning electron microscope.

Statistical Analysis
The presented data represents the mean values.Statistical analysis was conducted using the WASP -Web Agri Stat Package 2.0 Software.The data presented in the tables and figures represent the means with standard errors (±) derived from four independent replicates of each treatment.

Growth Parameters
The tiller population was recorded at 148103/ ha by (T 7 ), followed by (T 6 ) and (T 4 ) at 146200 tillers/ha and 1,44,570/ha respectively Table 2.The results were consistent with findings of [40] who reported that Si effect was time-dependent and became significant when the crop advances.Additionally, leaves containing Si exhibited a higher level of polysaccharides in the cell wall compared to those without Si.
The data regarding the effects of treatments on leaf area index, specific leaf area and specific leaf weight are presented in Table 2.The leaf area index was observed to be maximum in (T 7 ) at 4.07, followed by T 6 (3.45) and T 5 (3.27).The (T 7 ) registered the maximum specific leaf area of 4.89 cm 2 g -1 and the maximum was with the treatment T 1 (control).Lower specific leaf area in T 7 indicates  higher thickness of leaf.The maximum specific leaf weight of 0.37g cm 2 was noticed in (T 7 ).Plant cells need silicon in an optimum amount for development and differentiation [41].Based on the above results we could evaluate the role of silica solubilizer along with application of silica and other nutrients for the optimum plant growth.Si application effectively promoted sugarcane growth by rebalancing the absorption and utilization of nutrients such as N, P, K, and Si [42,43].There are many reports in literature explaining the role of microbes in nutrient absorption.Microorganisms have been recognized for their significant role in the dissolution of minerals such as silicates and phosphates [18,44].Numerous beneficial microbes have been identified for their positive effects on plants, especially under different stress conditions, by facilitating the improved uptake of these minerals [19].The solubilization of insoluble silicon and phosphate through the production of organic acids by microbes is known to enhance their availability to plants [45].
The results shown in Table 3 demonstrated that all treatments that were rich in organic silicon nutrients significantly improved the cane fresh and dry weight (g/plant) of the sugarcane crop, which also altered the ratio of dry weight to fresh weight.The treatment (T7) demonstrated the highest mean fresh weight of 1633 g/plant, as well as the highest mean dry weight of 1163 g/plant.Moreover, it exhibited the greatest percentage of dry weight compared to fresh weight, with a value of 28.78%.These values surpassed those of other treatments and the control group, indicating the superior performance of T7 in terms of plant growth and biomass production.Similar findings were made by [46] who demonstrated that the summer yield of maize fertilized with Si increased in comparison to the control treatment.

Nutrients Uptake
SEM and EDAX analysis study has shown significant differences among treatments in Si accumulation and other nutrients in sugarcane leaf blades Fig. 1.The highest concentration of silicon, and potassium was recorded by the (T7) against the control which showed only negligible values in leaves.At 210 DAP, the maximum nitrogen uptake value of 259.87 kg/ha was accounted for (T7) Table 4.However, the values were comparable with the treatments (T6) and (T5).In this study, the silicon applied to the leaves gave the highest nitrogen, phosphorous, and potassium content, because it prevented N loss through leaching and led to nitrogen being accumulated.Among the treatments, the (T 7 ) registered the higher phosphorous  Similarly, among the treatments, the (T 7 ) registered the higher potassium uptake of 415.35kg/ha on 210 DAP.These results suggest that plants treated with silicon along with silica soubilizer bacteria accumulate more silica and other nutrients in epidermal layers than non treated plants.Our experimental data using EDAX analysis were in agreement with that of [40,47,48] who reported that Si accumulation improved nutrient contents in leaves in monocots (rice, wheat and sugarcane).The soil is highly silicate with particles of both primary and secondary minerals.The biological breakdown of silicates liberates silicon in a soluble form in addition to potassium and phosphorus from fixed minerals [49][50][51].The effects of Si application on sugarcane absorption and utilization of N, P, and K shows that Si could rebalance mineral nutrients and, indeed, promote plant growth [52].

Quality Parameters
Our results demonstrated that potassium silicate fertilizer application (T7) increased brix percent (19.96), pol percent (10.37), purity percent by 94.92 and finally increased commercial cane sugar (CCS) to 11.81% Fig. 2. Significant variations among the varied organic and inorganic silicon sources practices were not observed.An insignificant variation in the value of Pol per cent was resulted with regard to the adopted various organic and inorganic silicon nutrients packages.Pol is the value determined by the polarimeter.Pol represents the quantity of sugar in the sugar solution.This suggested that Si improved the photosynthesis efficiency of individual plants as well as increased plant size.The Sucrose is converted in other forms of sugar compounds, which reduces cane weight and sugar contents.Use of silicon for sugarcane helps storage of sugar and prevents inversion of sugar in different sugar compounds [53].Which helps the reduction in loss of sugar and cane weight.Our present finding is in accordance with [54] where he observed that application of slag increased cane and sugar yields by 68% and 79% in plant crops, and by 125% and 129% in the ratoon crop, respectively.The Si fertilization increased the total recoverable sugar, stalks, and total sugar yields up to 21, 20, and 47%, respectively.Several beneficial effects of Si in sugarcane have been suggested to increase the crop yield, including the formation of silicon deposits in leaves and stalk that keeps the plant erect and improves photosynthesis [55].

Residual Soil Nutrient Analysis
The resulting values of soil residual organic carbon content concerning different organic and inorganic silicon nutrients revealed significant variations which are furnished in Fig. 3.Among the treatments, the highest residual soil nitrogen availability was obtained with regard to (T 7 ) with 227.90 kg ha -1 , which was comparable with the T 6 and T 5 .The (T 7 ) registered the highest residual soil phosphorus availability of 27.36 kg ha -1 which was on par with the integrated (T 6 ) and (T 5 ) treatments.The maximum residual soil potassium availability of 264.22 kg/ha was accounted for with the (T7) followed by (T 6 ) and (T 5 ) treatments.Our results of post harvest soil analysis are corroborated with [49][50][51].Further, there are studies to confirm the increased availability of nitrogen, phosphorus and potassium in soils amended with amorphous silicabased fertilizers [56,56,57,59].

Conclusion
The significance of silicon as a beneficial nutrient for sugarcane cultivation has generated a considerable interest.Our results also conclude that the soil and foliar application of silicon in sugarcane hold significant importance in its overall growth and yield.Silicon treatment to both the soil and leaves has found substantial improvements in the uptake of silicon and NPK along with enhanced plant growth and quality parameters when compared to the control group.These study findings hold great value in the development of effective nutrient management strategies specifically tailored for the intensive sugarcane farming soils of Tamil Nadu, India.

Fig 1
Fig 1 SEM with EDAX image of sugarcane leaves

Fig. 2 Fig. 3
Fig.2Effect of organic and inorganic silicon nutrients on sugarcane quality parameter under drought condition

Table 1
Initial soil properties of field experiment

Table 2
Effect of organic and inorganic silicon nutrients on growth and physiological parameters of sugarcane crop under drought condition (pooled mean value of plant and ratoon crop) Data are means ± standard error of seven independent experiments with three replicates in each experiment.Different letters show significant differences p<0.05 significance level treatments according to Duncan's multiple test

Table 3 Cane
yield (fresh, dry weight (g/plant) and (DW vs FW (%) of sugarcane crop as influenced by organic and inorganic silicon nutrients (pooled mean value of plant and ratoon crop) Data are means ± standard error of seven independent experiments with three replicates in each experiment.Different letters show significant differences p<0.05 significance level treatments according to Duncan's multiple test

Table 4
Effect of organic and inorganic silicon nutrients on Nutrient Uptake of sugarcane crop under drought condition (pooled mean value of plant and ratoon crop) Data are means ± standard error of seven independent experiments with three replicates in each experiment.Different letters show significant differences p<0.05 significance level treatments according to Duncan's multiple test uptake of 103.19 kg/ ha on 210 DAP.The integration of 2.5% urea and potash foliar spray on 15 days interval from 60-150 DAP registered the lowest values of 65.85 Kg ha -1 .The importance of silica in phosphorus nutrition is also emphasized because it has a close relationship with phosphorus.Silicon ions, removed from a low-pH soil by soluble silicate, increase available P by dislodging adsorbed P ions.