Influence of Chemical, Organic, and Biological Silicon Fertilization on Physiological Studies of Egyptian Japonica Green Super Rice (Oryza sativa L.)

Abstract

Rice plants are known to be silicon (Si) accumulators, hence farmers often use specific commercial chemical fertilizers to meet the nutrient needs of plants. Farmers commonly use fertilizers that are expensive and produce immediate effects, yet they contaminate the soil, water, and air. We should reduce the use of chemical fertilizers by combining a part of them with alternative organic and biological sources of Si, such as rice husk and Bacillus mucilaginosus (Si-solubilizing bacteria). Furthermore, it rationalizes chemical fertilizer consumption, reduces environmental pollution, and improves nutrient use efficiency to achieve rationalization of consumption with economic benefits in spending and rationalization of consumption of chemicals polluting the environment. In two successive growth seasons, 2021 and 2022, a field experiment was conducted to determine the effects of chemical, organic, and biological silicon fertilization in physiological studies of Egyptian Japonica green super rice. A randomized complete block design was used, with four replications, and the following treatments were used: T1, recommended dose of silica gel (SG; chemical Si); T2, recommended dose of rice husk (RH; organic Si); T3, recommended dose of Si-solubilizing bacteria (SSB; Bacillus mucilaginosus; biological Si); T4, ½ SG + ½ RH; T5, ½ SG + ½ SSB; T6, ½ RH + ½ SSB; T7, ¹/₃ SG + ¹/₃ RH + ¹/₃ SSB; T8, zero chemical, organic, and biological Si (control). The results showed that the application of silica gel as a chemical Si fertilizer, rice husk as an organic Si fertilizer, and Bacillus mucilaginosus as a Si-solubilizing bacteria or biological Si fertilizer source resulted in significantly higher yields of grain (10.71 and 10.53) t ha⁻¹ and straw (12.66 and 12.37) t ha⁻¹ in 2021 and 2022, respectively. Following that, silica gel, when combined with Si-solubilizing bacteria, led to increases in grain yield output of 10.32 and 10.39 t ha⁻¹ and straw yield of 12.16 and 12.05 t ha⁻¹ in 2021 and 2022, respectively. In addition, yield attributes, chlorophyll content in leaves, flag leaf area, flag leaf weight, chlorophyll in flag leaf, crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR), and silicon uptake in grain and straw were determined as follows: The application of silica gel as a chemical Si fertilizer, rice husk as an organic Si fertilizer, and Bacillus mucilaginosus as a Si-solubilizing bacteria or biological Si fertilizer source had a substantial impact on all examined characteristics. According to the optimal treatment, one part of the three parts of Si fertilization utilized just chemical Si fertilizer and the other two parts organic and biological Si. So we can minimize chemical fertilizer use and reduce soil pollution. The findings of this study will be valuable for future research, such as the usage of alternative organic and biological sources of Si in rice.

1. Introduction

Rice has supplied food to more people throughout history than other crop. It is the principal source of nutritional energy. It is now the second most cultivated cereal after wheat [1]. Egyptian Japonica green super rice (EJGSR) is one of the Japonica rice varieties that is very productive, drought- and salinity-tolerant, water-conserving, and maintains productivity at low fertilizer levels, thus protecting the soil, water, and air from pollution [2]. With all of this, this variety has the highest productivity per hectare when compared to locally grown varieties, and increasing its productivity by using lower chemical fertilizers will help to achieve the goals of Vision 2030 in terms of ensuring food security for humanity for years to come in a way that is green, environmentally friendly, contributes to reducing environmental pollution with chemicals, and reduces spending, thereby helping from an economic perspective [2]. To conserve this promising rice variety and safeguard the ecosystem where it is grown, we, therefore, need to identify the optimal fertilization and farming practices.

Silicon (Si) is a helpful element for rice plants that is typically absorbed in a greater amount than important nutrients such as nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) [2]. Si is not a free element; rather, it is bound to other elements to form chemical compounds such as silicon dioxide (SiO₂) [3]. Si, a metalloid element, makes up about 29% of the solid earth’s crust [4], and is the second most abundant element there after oxygen [5]. Rice is one of the farmed crops that is most susceptible to Si deficiency because it grows in flooding conditions. Among all crops, rice requires the most water. Compared to rice plants growing in nutrient solutions that were significantly supplied with Si, Si-deficient plants were physically weaker, more vulnerable to insect and disease attacks, and generated less biomass [6]. Si fertilizer affects plants and soil differently throughout the soil–plant system. The plant’s defenses against biotic and abiotic stresses are first strengthened. Second, increasing the soil’s physical, chemical, and water contents, and the availability of nutrients in plant-available forms, are all benefits of adding biogeochemically active Si compounds [7]. Si has been widely reported to improve rice water status by increasing root water uptake (rather than by reducing water loss) under conditions of water deficiency through the activation of osmotic adjustment, improving aquaporin activity, and increasing the root/shoot ratio [8]. Si has also been reported to improve plant water status and water balance under a variety of stress conditions, especially under drought and salt stresses. Si deposition in the outer walls of epidermal cells on both leaf surfaces prevented water loss through reduced transpiration and preserved normal growth in rice under drought stress [9,10]. In rice, Si can lower transpiration by 30% [7,10]. Si has been utilized to increase the availability of nutrients such as N, P, K, calcium (Ca), magnesium (Mg), sulfur (S), and zinc (Zn), as well as to reduce mineral stress caused by the toxicity of nutrients such as iron (Fe), aluminum (Al), manganese (Mn), cadmium (Cd), and arsenic (As) [11]. In tissues of stressed plants, Si increased the level of proline. Proline is an amino acid that functions primarily as a metal chelator, an antioxidant defense molecule, and a signaling molecule during stressful situations [12,13,14]. Si reduces harmful levels of Al and Mn and lessens the toxic effects of heavy metals and micronutrients [15,16]. The application of Si has been shown to decrease Mn toxicity in rice [17], Cd toxicity in rice [18], the concentration of free Al³⁺ in soil solution, and the concentration of Al³⁺ in straw, shoots, flag leaves, and husks by up to 50%. Intensive agricultural practices, leaching, and weathering all encourage soil silica removal and desilication [19,20]. Plants absorb Si from soil or water and release it either directly through leaf fall, indirectly through manure and animal or human feces, or indirectly through being chopped, utilized, and burned. The content of silicon in plants can range from 0.1 to 10% on a dry weight basis [21,22]. Despite an adequate amount of silica (SiO₂), the rate of silica dissolution is relatively low, resulting in a very low concentration of silica in soil solutions (0.1–0.6 mM) [23]. The plant-available form of silicon, monomeric silicic acid H₄SiO₄, predominates in soil solution [24]. Additionally, the Si accumulation in various plant components can vary greatly. For instance, different parts of the same plant can show large differences in Si accumulation: 0·5 g kg⁻¹ in polished rice, 50 g kg⁻¹ in rice bran, 130 g kg⁻¹ in rice straw, 230 g kg⁻¹ in rice hulls to 350 g kg⁻¹ in rice grain [25]. Si fertilization reduced the occurrence of blast and sheath blight in rice [26]. Increased Si uptake reduced the incidence of leaf folders and rice blast disease [27]. The addition of silica lowered lodging in rice, which boosted rice yield [28,29]; the lodging index of rice plants treated with silica dramatically decreased when compared to control plants, and silica-treated plants had a yield gain of 15.1%. Si increased photosynthesis, improved cell wall thickness beneath the cuticle, and improved leaf angle, making plants more upright and reducing shadowing, particularly under high nitrogen rates [30]. Plants absorb silicon (Si) as silicic acid, which is then transferred to the shoot where it is polymerized into silica gel on the surface of leaves and stems. The physiological function of Si in plant metabolism is not well supported by evidence. The epidermal cell walls of leaves, stems, and hulls contain more than 90% of the total silicon (Si) in the shoots as silica gel, generating a double layer of Si-cuticle and Si-cellulose [2]. Silica gel (SiO₂ · nH₂O) will polymerize when exposed to silicic acids, which will then transport it with water. Due to transpiration and polymerization, Si’s translocation occurs. Silicic acids undergo polymerization to generate colloidal silicic acids, which are then transformed into silica gel that adheres to the epidermis [21]. The absorbed silica will accumulate as a silica gel coating on the surface of the epidermal cell wall, which will grow thicker and more durable with time [31]. Plants have a layer of silica gel, also known as a phytolith, that is as hard as a rock [32]. Si preserves the shape of the cell during cell elongation and division by enhancing the structural stability of the cell walls [33]. As the plant tissue is not shielded by a layer of silica, plants lacking Si may experience slower growth and reduced yields [34].

The world’s supply of food depends on fertilizers. Rice plants are regarded as a “major silicon accumulator” [23], hence farmers often employ particular commercial chemical fertilizers to meet the nutrient needs of the plants. Farmers frequently use these fertilizers since they are cost effective and yield immediate results [35]. The organic supply of Si, like rice husk, and biological sources such as silicate-solubilizing bacteria, should be considered as alternatives. In a lot of countries that produce rice, such as Egypt, rice husk (RH) is one of the most widely accessible agricultural solid wastes. Nearly four million tonnes of rice are produced in Egypt each year. Because rice requires silica for good growth, using silica in rice husks as an organic fertilizer is the ideal technique for recycling rice husks [22,36]. The heating temperature and time significantly impact the amount of silica in rice husks [37]. It is 75–80% cellulose, hemicellulose, and lignin, with the remaining being silica (SiO₂) [38,39]. By enabling insoluble silicate minerals to dissolve, we can improve soil fertility and plant defense systems against plant diseases [40]. By increasing the amount of potassium absorbed by the plants, the bacterial silicate has been said to positively affect plant growth [41]; silicate bacteria inoculation of the soil was a significant influence in the development of plants that absorb potassium and silicon. These bacteria have the ability to both directly and indirectly combat phytopathogenic fungi. Directly, they do this by inhibiting the growth of fungal pathogens, while indirectly, they do this by increasing the amount of silicon in the soil, which causes plants to become disease resistant by acting as a modulator of host resistance to pathogens by mechanically impeding fungi penetration [42,43]. This research intends to use the most effective Si absorption forms from chemical, organic, and biological sources to address the physiological requirements of the rice while safeguarding the land and environment from contamination.

2. Materials and Methods

2.1. Experiment

In the seasons of 2021 and 2022, a field experiment was carried out at the Sakha Agricultural Research Station’s experimental farm in Kafrelsheikh, Egypt (30°57′12″ north latitude, 31°07′19″ east longitude), to evaluate the influence of chemical, organic, and biological silicon fertilization on physiological studies of Egyptian Japonica green super rice. At depths of 0 to 30 cm below the soil surface, representative soil samples were obtained from each site. After being air-dried, the samples were thoroughly combined and crushed to fit through a 2 mm sieve. The methodologies for soil analyses in [44] were followed. The experimental site’s soil physiochemical results for the 2021 and 2022 growing seasons revealed clayey soil with an organic matter level of 1.48 and 1.51; pH (1:2.5 water suspension) 8.07 and 8.1; Ec (ds m⁻¹) 2.14 and 2.21; available NH₄⁺ (mg kg⁻¹) 13.23 and 13.57; available P (mg kg⁻¹) 11.97 and 12.08; available K (mg kg⁻¹) 366 and 371; available micronutrients (mg L⁻¹): Fe²⁺ (5.04 and 4.97), Mn²⁺ (2.96 and 3.11), Zn²⁺ (1.1 and 1.08); soluble anions (meq. L⁻¹): HCO₃⁻ (16.33 and 16.81), Cl⁻ (15.21 and 15.17), SO₄² (2.44 and 2.76); and soluble cations (Meq. L⁻¹): Ca²⁺ (7.86 and 7.34), Mg²⁺ (3.88 and 4.02), K⁺ (1.13 and 1.04), Na⁺ (11.78 and 12.01). The rice variety used was JRL-23 Line (Sakha Super 300). The JRL-23 line was registered by the Egyptian Ministerial Resolution No. 1115 of 2018 under the trademark Sakha Super 300 rice variety, Egyptian Japonica green super rice (EJGSR). Sakha Super 300 is a medium grain, medium maturity rice variety, with high-yielding productivity, drought- and salinity tolerance, is water conserving, and displays productivity stability at low fertilizer levels. It was produced by the Rice Research and Training Center, Sakha Research Station, Kafrelsheikh, Egypt [2]. The seeds were soaked in water for 24 h before being incubated at a rate of 96 kg ha⁻¹ for 48 h to encourage early germination. In both seasons, pre-germinated seeds were evenly dispersed around the nursery on May 10. Plowing and subsequent wet-leveling were used to prepare the permanent field. Thirty days after sowing, rice seedlings were carefully taken out of the nursery and placed in field plots. They were then physically transplanted into 12 m² subplots, leaving 20 × 20 cm intervals between the rows and hills at the three seedlings per hill. The plots were kept submerged from transplanting until two weeks before harvest. Two weeks prior to harvest, water was once again removed from the plots [2,10].

2.2. Inorganic Fertilizers

As the recommended dosage of EJGSR, a chemical nitrogen fertilizer in the form of urea (46.5% N) was applied at a rate of 165 kg N ha⁻¹. Each plot received two doses of urea, with the first dose being two-thirds of the amount, serving as a basal application. The remaining one-third of the dosage was utilized as a top-dressing 30 days after transplanting (DAT). In addition, a chemical phosphorus fertilizer in the form of single super phosphate (SSP) with 15.5% P₂O₅ was added and well integrated into the soil as a basal application at the rate of 36 kg ha⁻¹, as the recommended dose for EJGSR [2].

At the time of final land preparation, chemical silicon fertilization was added and thoroughly incorporated into the soil as a basal application at a rate of 170 kg h⁻¹. The active material of this fertilizer was SiO₂, which included silica gel (SG), a gelatinous material whose main constituent is silicic acid, H₄SiO₄.

The important properties of the used silica gel are as follows: semitransparent gel appearance, SiO₂ (29%), overall porosity (72%), density (0.98 g cm⁻¹), pH (6.8–7.3), Ec (91 ds m⁻¹).

2.3. Organic Fertilizers

Organic silicon fertilization was used at a rate of 7 t ha⁻¹ of rice husk (RH), which was carried to plots and absorbed into the dry soil surface before rice transplantation [16,22].

2.4. Biofertilizers

Utilizing silicate-dissolving bacteria at a rate of 3.150 kg ha⁻¹, including Bacillus mucilaginosus, silicon-solubilizing bacteria (SSB) were inoculated. Thirty days after seeding, it was top-dressed while transplanting it into the permanent field. Enough sand was added to the inoculation powder to facilitate homogeneous dispersion. The Biofertilizers Unit, Faculty of Agriculture, Ain Shams University, Cairo, Egypt, provided the bacterial strain. The Rice Research and Training Centre recommended keeping to traditional rice-growing practices [2].

2.5. Treatments

To evaluate which of the different treatments was the optimal Si source for rice and soil, experiments were conducted using a randomized complete block design with four replications in two seasons, 2021 and 2022. The treatments examined were as follows: T₁, full dose of silica gel as chemical silicon (Si) fertilizer source; T₂, full dose of rice husk as organic Si fertilizer source; T₃, full dose of Bacillus mucilaginosus (Si-solubilizing bacteria; SSB) as bio-Si fertilizer source; T₄, ¹/₂ silica gel + ¹/₂ rice husk; T₅, ¹/₂ silica gel + ¹/₂ SSB; T₆, ¹/₂ rice husk + ¹/₂ SSB; T₇, ¹/₃ silica gel + ¹/₃ rice husk + ¹/₃ SSB; and control (without any chemical, organic, or biofertilizers).

2.6. Studied Characteristics

At sampling dates 60, 75, 90, and 105 days after transplanting, plants from five hills were randomly selected from each plot to calculate crop growth rate (CGR) in g m⁻² week⁻¹, relative growth rate (RGR) in g g⁻¹ week⁻¹, and net assimilation rate (NAR) in g m⁻² week⁻¹. These values were calculated as follows:

$$\begin{array}{c}\mathrm{C}\mathrm{G}\mathrm{R}=(\mathrm{W}2-\mathrm{W}1)/\mathrm{T}2-\mathrm{T}1\\ \mathrm{R}\mathrm{G}\mathrm{R}=(\mathrm{l}\mathrm{n}\mathrm{W}2-\mathrm{l}\mathrm{n}\mathrm{W}1)/\mathrm{T}2-\mathrm{T}1\\ \mathrm{N}\mathrm{A}\mathrm{R}=(\mathrm{W}2-\mathrm{W}1)(\mathrm{l}\mathrm{n}\mathrm{A}2-\mathrm{l}\mathrm{n}\mathrm{A}1)/(\mathrm{A}2-\mathrm{A}1)(\mathrm{T}2-\mathrm{T}1)\end{array}$$

where W1 and A1, and W2 and A2 are the dry weight and leaf area, respectively, at times T1 and T2 in weeks.

The total content of chlorophyll was evaluated using a chlorophyll meter (Model-SPAD502 Minolta Camera Co. Ltd., Osaka, Japan). The chlorophyll concentration of ten leaves was tested at 60, 75, 90, and 105 days after sowing (DAS). Ten flag leaves were chosen at random from each plot at the heading stage (90 DAS) and their area was measured with a portable area meter (Model LI—3000A), and the average flag leaf area (cm²) was recorded. The ten flag leaves were washed and oven-dried to a constant weight for 72 Co to calculate their dry weight. The total chlorophyll content in the flag leaf was determined using a chlorophyll meter (Model-SPAD502 Minolta Camera Co. Ltd., Osaka, Japan). At the heading stage, ten primary flag leaves were chosen at random and their chlorophyll contents were measured. At harvest, ten panicles from ten hills from each plot were measured to determine panicle length (cm), 1000-grain weight (g), percentage of full grains, and panicle number m⁻². At full maturity, the plants in each plot’s six inner rows were harvested separately, dried, and threshed, and the grain yield was adjusted to 14% moisture content. The yields of grain and straw were recorded and translated into t ha⁻¹. After harvest, dried samples of grain and straw were crushed to powder and digested [45], allowing the silicon concentration (Si%) in the grain and straw to be estimated [46]. Then, the silicon uptake (kg ha⁻¹) was calculated as follows:

$$\mathrm{S}\mathrm{i} \mathrm{U}\mathrm{p}\mathrm{t}\mathrm{a}\mathrm{k}\mathrm{e} \left(\mathrm{k}\mathrm{g} {\mathrm{h}\mathrm{a}}^{-2}\right)=\mathrm{S}\mathrm{i} \% \mathrm{i}\mathrm{n} \mathrm{g}\mathrm{r}\mathrm{a}\mathrm{i}\mathrm{n} \mathrm{o}\mathrm{r} \mathrm{s}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{w}\times \mathrm{d}\mathrm{r}\mathrm{y} \mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t} \mathrm{o}\mathrm{f} \mathrm{g}\mathrm{r}\mathrm{a}\mathrm{i}\mathrm{n} \mathrm{o}\mathrm{r} \mathrm{s}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{w}$$

2.7. Statistical Analyses

The data were statistically analyzed using the analysis of variance (ANOVA) approach of the randomized complete block design (RCBD) in four replicates [47]. The treatment means were compared using Duncan’s multiple range test [48]. All statistical analyses were performed using the “MSTAT-C” computer software package [49,50].

3. Results

3.1. Chlorophyll Content

Table 1. Influence of chemical, organic, and biological silicon fertilization on chlorophyll content in leaves of Egyptian Japonica green super rice.

Treatment	Chlorophyll (SPAD) at 60 DAS		Chlorophyll (SPAD) at 75 DAS		Chlorophyll (SPAD) at 90 DAS		Chlorophyll (SPAD) at 105 DAS
	2021	2022	2021	2022	2021	2022	2021	2022
SG (recommended)	41.75 cd	42.76 b	42.97 c	43.00 c	39.06 d	38.17 d	36.66 c	36.43 bc
RH (recommended)	38.14 e	39.68 d	41.67 d	40.12 e	37.55 f	36.91 f	35.56 e	34.78 d
SSB (recommended)	38.00 e	38.90 e	40.81 e	39.25 f	37.11 f	36.32 fg	34.77 f	34.22 de
½ SG + ½ RH	41.88 c	43.12 ab	43.01 bc	43.87 b	39.77 c	39.55 c	37.16 bc	36.90 b
½ SG + ½ SSB	42.11 b	43.30 ab	43.66 b	44.17 ab	40.91 b	40.78 b	37.69 b	38.00 ab
½ RH + ½ SSB	40.09 d	41.15 c	42.45 cd	42.93 d	38.65 e	37.72 e	36.03 d	35.14 c
1/3 SG + 1/3 RH + 1/3 SSB	43.50 a	43.65 a	44.13 a	44.73 a	41.35 a	41.60 a	38.50 a	38.77 a
Control	37.10 f	37.66 f	39.41 f	38.16 g	36.44 g	36.00 g	34.12 g	33.72 e
F. test	**	**	**	**	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. DAS: days after sowing. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor are designated at p ≤ 0.05 level using Duncan’s multiple range test.

illustrates the chlorophyll content of Egyptian Japonica green super rice leaves at 60, 75, 90, and 105 days from sowing as impacted by chemical, organic, and biological silicon (Si) fertilization in the 2021 and 2022 seasons. The application of a mixture of silica gel as a chemical Si fertilizer + rice husk as an organic Si fertilizer + Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source significantly improved the chlorophyll content in leaves during all growth stages, as well as reducing the amount of chemical Si fertilizer that was used on the soil. The second-best treatment was silica gel mixed with Si-solubilizing bacteria, while 0% chemical, organic, or biological Si fertilization produced the lowest results.

3.2. Flag Leaf

Table 2. Influence of chemical, organic, and biological silicon fertilization on flag leaf at heading stage of Egyptian Japonica green super rice.

Treatment	Flag Leaf Area (cm2) at Heading		Flag Leaf Chlorophyll (SPAD) at Heading		Flag Leaf Dry Weight (g) at Heading
	2021	2022	2021	2022	2021	2022
SG (recommended)	18.03 d	17.57 c	35.00 c	35.67 d	1.68 cd	1.52 d
RH (recommended)	15.52 f	15.12 e	33.65 e	34.59 f	1.55 e	1.35 f
SSB (recommended)	15.22 f	14.11 f	33.05 f	33.90 g	1.49 f	1.31 f
½ SG + ½ RH	18.81 c	18.00 bc	35.19 c	36.14 c	1.70 c	1.68 c
½ SG + ½ SSB	19.29 b	18.35 b	36.21 b	37.54 b	1.84 b	1.77 b
½ RH + ½ SSB	16.77 e	16.32 d	34.11 d	35.00 e	1.60 d	1.44 e
1/3 SG + 1/3 RH + 1/3 SSB	20.34 a	19.59 a	37.50 a	38.11 a	1.91 a	1.86 a
Control	14.63 g	13.62 g	32.10 g	31.88 h	1.39 g	1.24 g
F. test	**	**	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

shows the effects of chemical, organic, and biological silicon (Si) fertilization in the 2021 and 2022 seasons on the flag leaf area, flag leaf chlorophyll content, and flag leaf dry weight of Egyptian Japonica green super rice at the heading stage. The flag leaf characteristics at the heading stage were significantly improved by the administration of a mixture consisting of rice husk, silica gel, and Bacillus mucilaginosus as a source of biological silicon fertilizer. The second-best therapy was a mixture of silica gel and microorganisms that can dissolve silicon and reduced the amount of chemical Si fertilizer used. The lowest flag leaf values were achieved with 0% chemical, organic, or biological Si fertilization.

3.3. Crop Growth Rate (CGR)

Table 3. Influence of chemical, organic, and biological silicon fertilization on crop growth rate (CGR) of Egyptian Japonica green super rice.

Treatment	CGR (g m−2 week−1)
	60–75 DAS		75–90 DAS		90–105 DAS
	2021	2022	2021	2022	2021	2022
SG (recommended)	90.91 cd	91.97 d	298.50 d	308.91 d	160.72 cd	158.15 d
RH (recommended)	76.81 e	80.13 f	279.97 f	289.56 f	143.66 e	145.49 f
SSB (recommended)	73.00 f	75.07 g	270.23 g	280.04 g	139.10 f	140.67 g
½ SG + ½ RH	91.86 c	92.04 c	301.68 c	312.08 c	161.45 c	162.11 c
½ SG + ½ SSB	93.22 b	93.91 b	338.11 b	331.47 b	167.13 b	165.66 b
½ RH + ½ SSB	88.90 d	89.34 e	288.37 e	292.31 e	155.51 d	147.11 e
1/3 SG + 1/3 RH + 1/3 SSB	96.54 a	97.11 a	341.35 a	337.40 a	171.04 a	168.16 a
Control	68.44 g	70.29 h	266.10 h	273.17 h	135.93 g	138.64 h
F. test	**	**	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

shows the crop growth rate of Egyptian Japonica green super rice in the 2021 and 2022 seasons as influenced by chemical, organic, and biological silicon (Si) fertilization at 60–75, 75–90, and 90–105 days from sowing. Under all treatments, the best crop growth rate stage was reported at 75–90 days from sowing. The use of a combination of silica gel as a chemical Si fertilizer + rice husk as an organic Si fertilizer + Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source considerably increased the crop growth rate across all growth periods. The second most effective treatment was silica gel combined with Si-solubilizing bacteria. The lowest results were obtained with 0% chemical, organic, or biological Si fertilization.

3.4. Relative Growth Rate (RGR)

Table 4. Influence of chemical, organic, and biological silicon fertilization on relative growth rate (RGR) of Egyptian Japonica green super rice.

Treatment	RGR (g g−1 week−1)
	60–75 DAS		75–90 DAS		90–105 DAS
	2021	2022	2021	2022	2021	2022
SG (recommended)	0.311 d	0.329 c	0.511 d	0.488 d	0.134 d	0.135 d
RH (recommended)	0.291 f	0.283 f	0.421 f	0.464 f	0.124 f	0.128 f
SSB (recommended)	0.280 g	0.274 g	0.407 g	0.420 g	0.120 g	0.123 g
½ SG + ½ RH	0.324 c	0.320 d	0.536 c	0.500 c	0.140 c	0.139 c
½ SG + ½ SSB	0.339 b	0.340 b	0.597 b	0.572 b	0.148 b	0.141 b
½ RH + ½ SSB	0.302 e	0.297 e	0.447 e	0.471 e	0.129 e	0.130 e
1/3 SG + 1/3 RH + 1/3 SSB	0.351 a	0.344 a	0.612 a	0.591 a	0.153 a	0.148 a
Control	0.261 h	0.254 h	0.398 h	0.401 h	0.116 h	0.120 h
F. test	**	**	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

reveals the relative growth rate of Egyptian Japonica green super rice in the 2021 and 2022 seasons as affected by chemical, organic, and biological silicon (Si) fertilization at 60–75, 75–90, and 90–105 days from sowing. The best relative growth rate stage was recorded at 75–90 days after sowing for all treatments. The usage of a mixture of silica gel as a chemical Si fertilizer + rice husk as an organic Si fertilizer + Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source boosted the relative growth rate throughout all growth periods significantly. Silica gel combined with Si-solubilizing bacteria was the second most successful treatment. With 0% chemical, organic, or biological Si fertilization, the lowest results of relative growth rate were observed.

3.5. Net Assimilation Rate (NAR)

Table 5. Influence of chemical, organic, and biological silicon fertilization on net assimilation rate (NAR) of Egyptian Japonica green super rice.

Treatment	NAR (g m−2 week−1)
	60–75 DAS		75–90 DAS		90–105 DAS
	2021	2022	2021	2022	2021	2022
SG (recommended)	16.05 c	15.00 cd	39.98 bc	38.00 bc	19.85 cd	18.67 c
RH (recommended)	14.91 de	14.30 de	38.04 d	37.28 cd	18.56 e	17.93 d
SSB (recommended)	14.10 e	13.47 e	37.35 e	36.72 d	18.03 ef	17.60 de
½ SG + ½ RH	16.11 b	15.13 c	40.11 bc	38.14 b	20.18 c	19.40 bc
½ SG + ½ SSB	16.96 ab	16.07 b	40.91 b	39.50 ab	20.88 b	19.77 b
½ RH + ½ SSB	15.33 d	14.42 d	38.43 c	37.44 c	19.22 d	18.30 cd
1/3 SG + 1/3 RH + 1/3 SSB	17.01 a	16.88 a	41.22 a	39.96 a	21.15 a	20.45 a
Control	13.45 f	12.89 f	36.66 f	36.12 e	17.35 f	17.05 e
F. test	**	**	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

shows how the application of chemical, organic, and biological silicon (Si) fertilization at 60–75, 75–90, and 90–105 days from sowing affected the net assimilation rate of Egyptian Japonica green super rice in the 2021 and 2022 growing seasons. For all treatments, the best net assimilation rate stage was between 75 and 90 days from sowing. The net assimilation rate was greatly increased during all growth periods when silica gel was used as a chemical Si fertilizer + rice husk as an organic Si fertilizer + Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source. The second most effective treatment involved silica gel combined with Si-solubilizing bacteria. The results of the net assimilation rate showed the lowest values with zero chemical, organic, or biological Si fertilization.

3.6. Yield Attributes

Table 6. Influence of chemical, organic, and biological silicon fertilization on panicle length, 1000-grains weight, percentage of filled grains, and number of panicles m⁻² of Egyptian Japonica green super rice.

Treatment	Panicle Length (cm)		1000-Grains Weight (g)		Filled Grains (%)		Number of Panicles m−2
	2021	2022	2021	2022	2021	2022	2021	2022
SG (recommended)	21.14 cd	19.92 d	28.00 c	29.00 bc	95.67 c	95.17 bc	548 cd	502 bc
RH (recommended)	19.73 e	18.85 e	27.00 de	27.86 d	94.89 d	94.11 d	511 e	413 d
SSB (recommended)	18.55 f	17.61 f	26.81 e	27.07 de	94.02 e	94.00 d	466 f	398 e
½ SG + ½ RH	21.94 c	20.76 c	28.13 c	29.12 bc	96.35 bc	95.68 b	553 c	527 b
½ SG + ½ SSB	22.34 b	21.55 b	29.17 b	29.78 b	96.95 b	96.13 ab	566 b	557 ab
½ RH + ½ SSB	20.88 d	19.04 de	27.15 d	28.73 c	95.02 cd	94.90 c	539 d	458 c
1/3 SG + 1/3 RH + 1/3 SSB	23.11 a	22.94 a	30.30 a	30.11 a	97.62 a	96.91 a	573 a	569 a
Control	17.81 g	17.00 g	25.67 f	26.18 e	93.73 f	92.96 e	410 g	362 f
F. test	**	**	**	**	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

displays how Egyptian Japonica green super rice’s panicle length, grain weight per 1000 grains, percentage of filled grains, and number of panicles per square meter changed in response to chemical, organic, and biological silicon (Si) fertilization in the 2021 and 2022 growing seasons. It shows that the utilization of a combination including rice husk, silica gel, and Bacillus mucilaginosus as a source of biological silicon fertilizer results in a considerable improvement in yield attributes. A combination of silicon-dissolving bacteria and silica gel was the second-best treatment. With 0% chemical, organic, or biological Si fertilization, the lowest yield attributes values were obtained.

3.7. Si Uptake

Table 7. Influence of chemical, organic, and biological silicon fertilization on silicon uptake in grain and straw of Egyptian Japonica green super rice.

Treatment	Si Uptake in Grain (kg ha−1)		Si Uptake in Straw (kg ha−1)
	2021	2022	2021	2022
SG (recommended)	27.45 d	25.14 d	291.14 d	273.13 d
RH (recommended)	23.57 f	21.68 f	255.37 f	230.14 f
SSB (recommended)	23.11 f	19.33 g	240.31 g	226.66 g
½ SG + ½ RH	29.33 c	26.91 c	310.43 c	281.52 c
½ SG + ½ SSB	30.81 b	27.56 b	335.67 b	306.77 b
½ RH + ½ SSB	24.26 e	23.62 e	270.15 e	261.19 e
1/3 SG + 1/3 RH + 1/3 SSB	32.11 a	30.85 a	341.11 a	338.15 a
Control	20.53 g	18.41 h	221.18 h	208.72 h
F. test	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

shows the uptake of silicon (Si) in Egyptian Japonica green super rice grain and straw in the 2021 and 2022 seasons as influenced by chemical, organic, and biological Si fertilization. The use of a combination of silica gel as a chemical Si fertilizer + rice husk as an organic Si fertilizer + Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source enhanced Si uptake in rice grain and straw considerably. The second-best treatment was silica gel mixed with bacteria that dissolve Si. The lowest results were obtained with 0% chemical, organic, and biological Si fertilization.

3.8. Grain and Straw Yields

As a result of chemical, organic, and biological silicon (Si) fertilization in the 2021 and 2022 growing seasons,

Table 8. Influence of chemical, organic, and biological silicon fertilization on grain and straw yields of Egyptian Japonica green super rice.

Treatment	Grain Yield (t ha−1)		Straw Yield (t ha−1)
	2021	2022	2021	2022
SG (recommended)	9.87 d	9.88 d	11.51 d	11.51 d
RH (recommended)	9.49 ef	9.57 f	10.93 f	11.04 ef
SSB (recommended)	9.33 f	9.22 g	10.77 g	10.93 f
½ SG + ½ RH	10.07 c	10.11 c	11.86 c	11.78 c
½ SG + ½ SSB	10.32 b	10.39 b	12.16 b	12.05 b
½ RH + ½ SSB	9.51 e	9.70 e	11.24 e	11.19 e
1/3 SG + 1/3 RH + 1/3 SSB	10.71 a	10.53 a	12.66 a	12.37 a
Control	9.15 g	9.04 h	10.68 h	10.51 g
F. test	**	**	**	**

SG: silica gel (chemical Si); RH: rice husk (organic Si); SSB: Si-solubilizing bacteria, Bacillus mucilaginosus (bio-Si); Control: zero chemical, organic, or biological Si. Columns with different lowercase letters indicate a significant difference at p ≤ 0.05. **, a significant effect at p ≤ 0.01. The means of each factor designated at p ≤ 0.05 level using Duncan’s multiple range test.

shows the grain and straw yields of Egyptian Japonica green super rice. The application of silica gel as a chemical Si fertilizer, rice husk as an organic Si fertilizer, and Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source resulted in significant increases in the grain yields (10.71 and 10.53) t ha⁻¹, and straw yields (12.66 and 12.37) t ha⁻¹ in 2021 and 2022, respectively. Then, the grain yields increased by (10.32 and 10.39) t ha⁻¹ and the straw yields by (12.16 and 12.05) t ha⁻¹ in 2021 and 2022, respectively, as a result of silica gel combined with bacteria that can solubilize silicon. However, in both 2021 and 2022, the lowest grain yields (9.15 and 9.04) t ha⁻¹ and straw yields (10.68 and 10.51) t ha⁻¹ were produced without chemical, organic, or biological Si fertilization.

4. Discussion

The combination of silica gel, rice husk, and Bacillus mucilaginosus as a Si-solubilizing bacteria lowered the amount of chemical Si applied to the soil while meeting the plant’s Si requirements using organic and biological Si sources. Furthermore, as a bio-Si source, Bacillus mucilaginosus may convert unavailable Si in the soil to an accessible and absorbable form [51,52]. Because silica absorbed by plants accumulates on the surface of the epidermal cell wall as a coating of silica gel, the stem becomes thicker and stronger [53]. By producing an inner protective shell, silica gel boosts plants’ defenses against external attack [54]. The same antioxidant defense mechanism was discovered in silica gel and rice husk [54,55]. Bacillus mucilaginosus enhance growth and cell development (primary and secondary metabolite activity) [56,57]. In rice, the combination of chemical, organic, and biological Si fertilization increased culm wall thickness, vascular bundle size, and peroxidase activity, resulting in increased stress tolerance, stem strength, and lodging resistance [58,59]. Flag leaf area, weight, and chlorophyll content increased after Si treatment due to increased Si concentration in the rice plants and the removal of large amounts of Si from the soil [60,61]. The use of Si influences plant development and production, which then supports plant stems to reduce plant breakdown [62]. Silicon fertilization is crucial for boosting plant disease resistance and maintaining healthy leaves [63]. The absorbed silica will accumulate on the surface of the epidermal cell wall in the form of a silica gel layer, thickening and strengthening it [21]. The deposition of Si in the outer walls of epidermal cells on both surfaces of leaves has been reported to reduce water loss by lowering transpiration and preserve normal growth under drought stress in rice [9]. Si can lower transpiration by 30% in rice [64,65]. Silicon application has been shown to lower Mn toxicity in rice [17], Cd toxicity in rice [18], and the concentration of free Al³⁺ in soil solution, as well as its concentration in straw, shoot, flag leaf, and husk, by up to 50% [2,19]. Chemical, organic, and biological Si enhanced the physiological characteristics of green super rice, including the rate of crop growth, the relative growth rate, and net assimilation rate. This is because rice absorbs silicon (Si) in the form of silicic acid, which is transferred to the shoot and, after water is lost, polymerizes to create a silica gel on the surface of leaves and stems. The epidermal cell walls of leaves, stems, and hulls contain silica gel, which makes up double layers of Si-cuticle and Si-cellulose, which contain more than 90% of the total Si in the shoots [66]. Proline levels in rice cultivars under water stress during the vegetative and reproductive stages tend to change when Si supplementation is used as a fertilizer; this is a sign of stress resistance [30,67]. Amorphous silica particles called phytoliths or plant opal, which precipitate in plant cells, are primarily responsible for the advantages attributed to Si. When silicic acid concentrations are more than 2 mM, it can be polymerized to create phytoliths without the use of any energy. As well as being present as silica bodies in bulliform cells, fusoid cells, or prickle hairs in rice, phytoliths are also found in particular cells known as silica cells that are positioned on vascular bundles [68,69]. Si plays a significant function in water as well, and crop plants absorb a significant amount of Si from irrigation water. Plants absorb silica from the soil solution in the form of silicic acid. Si can be transported by irrigation from the exterior solution to the root cells and then from the root cells to the apoplast [51,56], and finally, from the primary vascular bundles to the panicles [60,70]. Additionally, rice husk’s composition, which is 75–80% cellulose, hemicellulose, and lignin with the remaining material being silica (SiO₂), has an impact on growth [38,39]. On the other hand, bacterial silicate has a positive impact on plant growth by increasing the amount of potassium that plants can absorb. Si-solubilizing bacteria inoculation of the soil was shown to be a major contributor to the rise in potassium and silicon uptake by plants [41,63]. Finally, the combination of silica gel, rice husk, and Si-solubilizing bacteria can enhance the physiological properties of crops and their relative growth, whereas plants without Si can have reduced growth and yield because their tissues are not covered by a layer of Si [40]. With the addition of chemical, organic, and biological silicon, yield attributes were improved. Si increased photosynthesis, improved cell wall thickness beneath the cuticle, and improved leaf angle, making the leaves more upright and reducing shade, especially when nitrogen rates were high [30]. For plants to be more resistant to environmental factors and diseases, silicon fertilization is crucial [55]. Silicon can boost rice plant development and yield [71]. Rice Si absorption increased by as much as 32% after soil application of Si-containing fertilizer [72,73]. Silica gel is a powerful adsorbent of heavy metals [74]. Silica was added to rice, which decreased lodging and enhanced rice yield [28,50]. Silica gel, and rice husk with Si-solubilizing bacteria can improve critical nutrients in plants by modifying the osmotic stress of the cell and preventing the buildup of free radicals [75,76]. When rice is grown in soils with low levels of plant-available silicon, Si-solubilizing bacteria fertilizer is added, increasing grain and straw yields [50]. Si fertilization raises yields by 10% to 25% [7]. The yields of straw and grain dropped by 20 and 50 percent, respectively, in rice plants that were denied Si throughout the reproductive stage, but these yields were increased by 24 and 30 percent, respectively, when the plants were provided with Si. Increased stem diameter and, thus, increased straw yield can be achieved through fertilization with silica gel and rice husk [2]. Silica gel material supports the oxidation of a variety of pollutants, hence balancing the ecosystem’s structure and functions [69]. Increased Si uptake decreased the occurrences of leaf folding and rice blast disease [27]; the lodging index of rice plants treated with Si was significantly lower than the control; and the yield of plants treated with Si was 15.1% higher [77].

5. Conclusions

According to this study’s results, using silica gel as a chemical Si fertilizer, rice husk as an organic Si fertilizer, and Bacillus mucilaginosus as a Si-solubilizing bacteria or bio-Si fertilizer source were the best ways to increase the production of Egyptian Japonica green super rice. The combination of silica gel with Si-solubilizing bacteria led to an improvement in rice yield and its physiological properties. It is possible to increase rice output and lower chemical fertilizer use by a third by integrating the three sources of silicon; chemical, organic, and biological. This reduces environmental pollution and increases nutrient use efficiency in order to rationalize consumption and minimize spending on chemicals that harm the environment. In achieving this, we can help to realize Vision 2030, which aims to achieve environmental sustainability. The results of this study will be helpful for further research, such as the use of alternative organic and biological sources of silicon in rice in various application forms and techniques.