Ortho Silicic Acid: A Novel Approach to Enhance Plant Nutrition and Quality in Fodder Maize

doi:10.21203/rs.3.rs-3216311/v1

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Research Article

Ortho Silicic Acid: A Novel Approach to Enhance Plant Nutrition and Quality in Fodder Maize

https://doi.org/10.21203/rs.3.rs-3216311/v1

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published 05 Oct, 2023

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Agriculture has neglected silicon (Si) fertilization due to the widespread belief that soil has enough of Si and it is beneficial under any kind of biotic or abiotic stress, often neglecting its usefulness under optimum and stress-free conditions. A two-year field experiment was conducted to evaluate the effect of foliar spray of orthosilicic acid (OSA) on the growth, yield, nutrient content, and quality of fodder maize. The experiment was conducted in Zaid season at the Research Farm of Agronomy Section, ICAR-National Dairy Research Institute, Karnal, India. Seven treatments with different concentrations of OSA (0.05%, 0.10%, 0.15%, 0.20%, 0.25%, and 0.30%) were applied along with the recommended dose of fertilizer (RDF). RDF without OSA application was used as control. The results showed that OSA application significantly improved green fodder yield (GFY) and dry fodder yield (DFY). The concentration of 0.25% OSA resulted in the highest GFY (53.63 t ha^− 1) and DFY (13.35 t ha^− 1), which were 10.6% and 45.3% higher than the control, respectively. The application of OSA also positively influenced growth parameters such as crop growth rate (CGR), relative growth rate (RGR), dry matter accumulation (DMA), leaf:stem ratio, and physiological parameters including SPAD (chlorophyll content), relative water content (RWC%), and leaf area index (LAI). OSA foliar spray improved the nutrient content and uptake in fodder maize. Nitrogen (N%), potassium (K%), and calcium (Ca%) concentrations were significantly increased with OSA application, while phosphorus (P%) concentration remained unaffected. The uptake of N, P, K, and Ca was also significantly higher in the OSA-treated plots, with the 0.25% OSA treatment showing the highest nutrient uptake. OSA application recorded higher dry matter (DM%), crude protein (CP%), total ash (TA%), and lower neutral detergent fiber (NDF%), and acid detergent fiber (ADF%). Economic analysis revealed that OSA at 0.25% concentration resulted in the highest gross return, net return, and benefit-cost ratio (B:C), indicating its economic viability. Therefore, foliar spray of OSA, at 0.25% concentration, improved the growth, yield, nutrient content, and quality of fodder maize. This study highlights the potential of OSA as a beneficial foliar spray for enhancing production and quality of fodder maize.

Orthosilicic acid (OSA)1

Silicon2

Fodder Maize3

Fodder quality4

Nutrient content5

Calcium6

AIA7

Economics8

After oxygen, silicon (Si) is the most common element in the Earth's crust (Luyckx et al. 2017). Silicon dioxide (SiO₂) is the primary form of silicon (Si) commonly found in soil. The soil also contains minerals like vermiculite, smectite, kaolin, orthoclase, feldspars, plagioclase, amorphous silica, and quartz, which contribute to its silicon content. These silicon forms have low solubility and remain largely immobile in the soil's biogeochemical processes. The main soluble silicon forms in the soil are poly- and monosilicic acids (Sahebi et al. 2015). However, monosilicic [Si(OH)₄] acid is mostly weakly adsorbed and has limited ability to migrate within the soil. Among the various forms of Si such as silicates, silicon dioxide, (mono- and poly-) silicic acid, and biogenic silica, only monosilicic acid is plant available, but due to its instability its concentration is very low (Laane 2018). It polymerizes and becomes non-bioavailable as concentration increases. The Si content in plants varies across species, ranging from less than 0.1% to over 10% of dry weight. Plant species are categorized based on their Si content: Si accumulators have Si levels above 1.0%, intermediate types have Si levels between 0.5% and 1.0%, and Si excluder types have Si levels below 0.5% (Takahashi et al. 1990). These variations result from differences in the roots' ability to absorb monosilicic acid (MSA) also called ortho silicic acid (OSA), with genotypic variations also present within the same species. In monocotyledonous plants, the uptake of OSA is an active process facilitated by Si transporters in the root wall (Laane 2018). On the other hand, in dicotyledonous plants, OSA uptake occurs through diffusion, leading to lower OSA concentrations in the xylem compared to monocots. Once taken up in the xylem, soluble OSA travels through the transpiration stream and is eventually deposited in various parts of the plant, including within or between cells and as part of the cell wall, such as in the leaf epidermis, where it forms silica (biogenic opal or phytoliths)(Sangster et al. 2001).

A sufficient uptake of OSA is crucial for plants as silicon offers multiple benefits, including providing structural strength, playing a role in various physiological processes such as regulating the uptake of other nutrients, supporting growth and development, and enhancing resistance to abiotic and biotic stresses. One of the roles of silicon in the uptake of essential plant nutrients is its ability to enhance the uptake of certain mineral nutrients (Pavlovic et al. 2021), such as phosphorous (P) and potassium (K). Silicon has been shown to improve the availability of P and K by increasing the cation exchange capacity (CEC) of the soil, which in turn promotes the adsorption and retention of these nutrients in the root zone. Moreover, silicon can also improve the plant’s tolerance to various abiotic and biotic stresses such as drought, salinity (Fernández-Escobar 2019), and pathogen attack. This can indirectly contribute to the uptake of essential plant nutrients by promoting plants growth and development, which in turn can increase the plant’s nutrient demand and uptake capacity. It can also be rightly said that most of the studies on Si is done under stress conditions, leaving meagre information on its performance under non–stressed condition which becomes the study area for this current experiment.

Applying orthosilicic acid (OSA) to the foliage can also boost the uptake and utilization of nitrogen (N), phosphorous (P), and potassium (K) in plants, and the mechanisms behind this process differ somewhat from those associated with soil application. Firstly, the application of OSA in the form of silicon (Si) has been found to enhance N uptake in various plant species, including rice, wheat, maize, and soybean, as demonstrated in a study published in the Journal of Plant Nutrition and Soil Science. This increase in N concentration was observed in both the shoots and grains of rice plants. Moreover, OSA can improve nutrient availability in the soil by facilitating the dissolution of insoluble minerals, such as phosphates, thereby releasing more P for plant uptake. Additionally, it enhances the solubility of K, making it more accessible for plants to absorb (Mali and Aery 2008). Furthermore, OSA enhances nutrient transport within plants by increasing the activity of ion transporters and channels in cell membranes. This assists in the movement of N, P, and K from the roots to the shoots and ultimately to the grain or fruit. Another benefit of OSA foliar application is its ability to stimulate metabolic processes in plants, leading to increased efficiency in nutrient uptake and utilization. For example, silicon has been shown to enhance photosynthesis, which consequently increases the demand for N, P, and K in plants, thereby improving their growth and yield.

In addition, OSA foliar application improves leaf structure, facilitating nutrient absorption through the leaf surface. The silicon layer formed on the leaf surface acts as a physical barrier, reducing water loss and promoting nutrient uptake. Overall, OSA foliar application stimulates metabolic processes, enhances nutrient transport, and improves photosynthesis in plants (Mali and Aery 2008). These effects lead to increased nutrient demand, uptake, and utilization, ultimately resulting in improved growth and yield. Plants deprived of silicon exhibit weaker structures, reduced growth, development, viability, and reproductive capacity. They are also more susceptible to biotic and abiotic stresses. Foliar application of (micro-) nutrients and bio-stimulants has become an important method of plant feeding, and in some cases, it proves to be more effective than soil application (Desoky et al. 2021). The rationale behind using foliar sprays with silicon compounds is that they can compensate for low root uptake in situations where absorbable silicon is scarce in the soil or when the root absorption process is complex, leading to increased silicon uptake and its associated benefits. The production of high-quality fodder is decisive to improve the health of livestock (Biswal et al. 2022). Some evidence suggests that foliar spray of ortho silicic acid (OSA) can positively impact the quality of fodder maize, which comprises essential components providing energy and nutrients to livestock, such as crude protein, ether extract, ash, and fiber fractions. OSA foliar spray enhance the crude protein and crude fiber content of fodder maize, thereby improving its nutritional value for livestock (Sonobe et al. 2010). On the other hand, the effect of OSA on ether extract (EE) content in plants is not extensively studied, and available research is limited. Further research is necessary to determine the optimal application rate and timing of OSA foliar spray for maximizing the benefits on fodder maize's nutritional value. Regarding the NDF (neutral detergent fiber) and ADF (acid detergent fiber) contents in forage and fodder crops, they are essential parameters determining their nutritional quality. Limited research exists on the effect of foliar silicon spray on NDF and ADF content in plants. However, some studies on forage crops indicate that silicon application can have a positive effect by reducing NDF and ADF contents. For instance, studies on grass–legume mixture showed that foliar silicon application significantly decreased their NDF and ADF contents (Borawska-Jarmułowicz et al. 2022). The mechanism behind this reduction is not fully understood but is believed to be related to silicon's role in enhancing cell wall structure and lignin metabolism in plants. Strengthening the cell walls can make plants more resistant to abiotic and biotic degradation, resulting in reduced NDF and ADF contents in forage crops. It is important to note that the effect of silicon foliar spray on NDF and ADF content may vary depending on plant species, application method, and environmental factors. Further research is required to fully comprehend silicon's impact on the nutritional quality of forage crops as the information relating to fodder and forages as very scanty. Therefore, after reviewing the benefits of OSA on plant, optimization of dose for foliar spray of OSA on fodder maize under non–stressed condition was chosen as the study area for this research.

2.1 Experimental site

The two consecutive years 2020–21 and 2021–22 of field experiment was conducted during Zaid season, at the Research Farm of Agronomy Section, ICAR–National Dairy Research Institute, Karnal, Haryana, India. The coordinates of Karnal are 29°43' North latitude and 76°58' East longitude in the subtropical zone. The soil type of the research field was clay loam with 7.06 neutral pH, 0.56% organic carbon, 0.312 dS m^− 1 EC, 202 kg ha^− 1 available N (low), 27.95 kg ha^− 1 available P (high), 210 kg ha^− 1 available K (medium) and 307.12 ppm available Ca. The Fodder maize crop was planted in the last week of April and harvested after 60 Days in the last week of June. In the previous season, wheat was grown. The fodder maize variety taken was J–1006 at spacing of 20 cm x 10 cm, and the net plot size was 5.5 m x 3.5 m. The area receives a mean annual rainfall of 690–720 mm and an average annual temperature of 23.8°C.

2.2 Treatment details

There were seven treatments replicated thrice in a completely randomized block design. T₁: RDF (recommended dose of fertilizer only without OSA foliar spray), T₂: 0.05% OSA, T₃: 0.10% OSA, T₄: 0.15% OSA, T₅: 0.20% OSA, T₆: 0.25% OSA and T₇: 0.30% OSA. OSA treatments were also applied along with RDF. OSA was foliar sprayed at 30 DAS. The product used as an OSA source was Silixol from Privi Life Sciences Pvt. Ltd. The product has 2.7% min. stabilized OSA with 0.80% min. Si content. The RDF for fodder maize is 120–26.2–33.3 kg ha^− 1 (NPK) was broadcasted. N was applied in two equal splits at basal and 30 DAS. The crop was grown as per the standard package of practices by line sowing, with timely irrigation and weeding.

Leaf: stem ratio was measured at 60 DAS by removing the leaves from five tagged plants and weighing the fresh leaves and stem separately. Dry matter accumulation (DMA) was recorded at 30 and 60 DAS by taking plants samples from second row (one meter length) of each plot sun dry followed by hot air oven at 65 ± 5°C till constant weight obtained. Crop growth rate (CGR) and relative growth rate (RGR) was calculated as per (Radford 1967) formula. SPAD value was recorded at hand held chlorophyll meter. Relative water content (RWC%) was expressed as percent moisture content in fresh leaf to moisture content at saturation and leaf area index (LAI) as given by (Watson 1947). Green fodder yield was recorded after harvesting each plot (eliminating border effect) and was dried in hot air oven at 65 ± 5°C for 48 hrs. Dry fodder yield was worked out by multiplying green fodder yield with its dry matter content.

The oven-dried plant samples were ground to pass through 40 mesh sieve in a Macro-Wiley Mill and used for chemical analysis. The sieved samples were analyzed for DM (AOAC 2005, method 934.01), total ash [TA (AOAC 2005, method 984.05)] and Kjeldahl nitrogen (AOAC 2005, method 984.13). Organic matter (OM) was calculated by subtracting TA content from 100. Ether extract (EE) was analyzed according to AOAC 2005, method 920.39. Crude protein content was determined by multiplying N concentration by 6.25. Acid insoluble ash (AIA) was estimated by AOAC 2005, method 941.12. Fibre fractions such as neutral detergent fibre (NDF) was analyzed by the method proposed by (Van Soest et al. 1991), acid detergent fibre (ADF) and acid detergent lignin (ADL) were analyzed by and AOAC (2005, method 973.18).

The sieved fodder maize samples were digested in a di-acid mixture (HNO₃:HClO₄ in 9:4 ratio) and the aqueous extract was used to determine phosphorous (P) with the ammonium vanado–molybdo phosphoric acid yellow color method (Jackson 1973), potassium (K) and calcium (Ca) with a flame photometer (Jackson 1973). Nitrogen (N) was analyzed by Modified Kjeldhal method. The uptake of nutrients in fodder maize is obtained by multiplying nutrient concentration with dry fodder yield.

2.3 Economics

The cost of cultivation with the price of inputs and operations, at the time of their use, is given in supplementary material. The selling price of green fodder maize was ₹150 q ha^− 1 in 2020–21 and ₹160 q ha^− 1 in 2021–22. The gross return was calculated by multiplying yield with price, net return by subtracting total cost of cultivation from the gross return and benefit: cost (B:C) ratio by dividing the net return by total cost of cultivation.

2.4 Statistical analysis

All the data recorded were analyzed with the help of ANOVA technique (Gomez and Gomez 1984) for a completely randomized block design using R software. Minimum significant difference (MSD) values were calculated by Tukey’s HSD (honestly significant difference) test at a 5% level of significance (P < 0.05). Principal component analysis (PCA) and correlations matrix between growth, yield, nutrient and quality were analyzed for the positive relationship over the whole data set using R software and JMP software (version 14.1).

3.1 Green and dry fodder yield of fodder maize

Two years of field experiments have showed that, the treatments with OSA foliar spray of concentration 0.15% and above were statistically at par with each other (Fig. 1a,b). In terms of green and dry fodder yield. 0.25% OSA recorded maximum 53.63 t ha^− 1 GFY i.e. 10.6% higher over only RDF (48.48 t ha^− 1). DFY was significantly improved due to OSA foliar spray with 0.20%, 0.25% and 0.30% OSA having comparable DFY. The control treatment with only RDF had the least DFY with 9.18 t ha^− 1.

3.2 Growth rate, DMA (kg m^− 2) and leaf: stem ratio of fodder maize

The effect of OSA application on fodder maize growth rate (CGR and RGR), DMA and leaf: stem ratio was promising in the two-year experiment (Fig. 1c–f). DMA was outstanding in 0.25% OSA compared to other concentrations of OSA at 60 DAS (1.69 kg m^− 2). The said treatment was 19.9% higher over RDF (1.41 kg m^− 2). CGR and RGR were comparable in concentrations 0.20% and above. CGR in 0.25% OSA (42.78 g m^− 2 day^− 1) was 26.8% higher over RDF (33.74 g m^− 2 day^− 1) and RGR (47.51 mg g^− 1 day^− 1) for the same OSA concentration was 12.6% higher over RDF (42.21 mg g^− 1 day^− 1). Leaf: stem ratio was significantly improved due to OSA foliar spray compared to control (0.31).

3.3 Fodder maize SPAD, RWC% and LAI at 60 DAS

During the study years, it was seen that foliar spray of OSA with concentration of 0.15% and above had significantly promising physiological parameters such SPAD, RWC% and LAI at 60 DAS (Fig. 2a,b). 0.25% OSA reported 5.7%, 7.7% and 11.1%, higher SPAD (42.55), RWC% (75.98%) and LAI (4.50) over RDF 40.25, 70.52% and 4.05 respectively.

3.4 Nutrient content and uptake in fodder maize

Si is known to improve nutrient concentration in plants, it is also proven by the present study where in N% in significantly improved from 0.20% OSA concentration and above (Fig. 3a). 0.25% OSA (1.442%) was 1.4% over RDF (1.422%). P% in fodder maize was not significantly improved due to the foliar spray of OSA (Fig. 3b). K% and Ca% like nitrogen concentration improved with OSA foliar application (Fig. 3c,d). 0.25% OSA (1.275%) reported maximum K% of 4.3% higher over RDF (1.222%). However, 0.30% OSA (0.034%) had the maximum Ca% of 2.4% higher over RDF (0.033%).

N, P, K and Ca uptake in fodder maize was significantly improved due to OSA foliar spray (Fig. 4a–d). 0.25% OSA reported the highest uptake of N (162.89 kg ha^− 1), P (25.11 kg ha^− 1), K (144.07 kg ha^− 1) and Ca (3.85.19 kg ha^− 1), higher by 24.2%, 31.1%, 28.6% and 25.8% over RDF 130.57 kg ha^− 1, 19.15 kg ha^− 1, 112.07 kg ha^− 1 and 3.06 kg ha^− 1 respectively.

3.5 Quality parameters of Fodder maize

In the present study, the effect of OSA improved the DM, CP, EE, TA, AIA and significantly decreased the fibre fractions such as NDF and ADF (Table 1). 0.20% OSA concentration and above performed well for all the above-said parameters. DM, CP and EE were 11.3%, 1.3% and 3.3% respectively higher in 0.25% OSA over RDF. OM% decreased due to OSA application. TA and AIA were 3.3% and 6.5% higher in 0.30% OSA compared to RDF. NDF and ADF in 0.30% OSA foliar spray were 2.0% and 2.7% lower compared to RDF. ADL was not significantly reduced due to OSA application.

Table 1

Effect of various concentration of ortho silicic acid (OSA%) on fodder maize quality parameters on dry wt. basis at harvest
Treatments	DM (%)	OM (%)	CP (%)	EE (%)	TA (%)	AIA (%)	NDF (%)	ADF (%)	ADL (%)
RDF	18.92^b ± 0.43	92.21^a ± 0.08	8.89^c ± 0.04	1.83^c ± 0.01	7.79^b ± 0.08	1.53^c ± 0.01	69.70^a ± 0.15	39.44^a ± 0.23	4.62
0.05%	19.03^b ± 0.43	92.21^a ± 0.07	8.89^c ± 0.03	1.86^bc ± 0.01	7.79^b ± 0.07	1.53^c ± 0.01	69.67^ab ± 0.31	38.77^ab ± 0.30	4.66
0.10%	19.62^ab ± 0.55	92.19^a ± 0.07	8.92^bc ± 0.03	1.87^ab ± 0.01	7.81^b ± 0.07	1.58^b ± 0.01	69.50^ab ± 0.38	38.70^ab ± 0.10	4.67
0.15%	20.20^ab ± 0.38	92.02^ab ± 0.01	8.97^abc ± 0.01	1.88^ab ± 0.01	7.98^ab ± 0.01	1.60^ab ± 0.02	69.20^abc ± 0.20	38.66^b ± 0.30	4.71
0.20%	20.35^ab ± 0.46	91.99^b ± 0.07	9.00^ab ± 0.01	1.88^ab ± 0.01	8.01^a ± 0.07	1.62^ab ± 0.01	68.78^bc ± 0.29	38.62^b ± 0.12	4.71
0.25%	21.06^a ± 0.53	91.96^b ± 0.03	9.01^a ± 0.02	1.89^a ± 0.01	8.04^a ± 0.03	1.63^a ± 0.01	68.40^c ± 0.15	38.56^b ± 0.30	4.72
0.30%	20.85^a ± 0.37	91.85^b ± 0.03	9.00^ab ± 0.04	1.88^ab ± 0.01	8.05^a ± 0.03	1.63^a ± 0.02	68.31^c ± 0.11	38.38^b ± 0.30	4.72
SEm(±)	0.33	0.04	0.02	0.008	0.04	0.01	0.20	0.17	0.07
MSD(P < 0.05)	1.48	0.20	0.09	0.036	0.20	0.05	0.90	0.78	0.33
Note: The pooled mean of two years data followed by the same lowercase letter(s) and standard error of mean within a column do not differ significantly at Tukey’s HSD (p < 0.05)

3.6 Correlation of green and dry fodder yield with Nutrient content and uptake

Green fodder yield (GFY) was positively and linearly related to dry fodder yield (DFY) (Fig. 5). Except for P content in green fodder, both GFY and DFY were significantly and positively related to N, K and Ca content and N, P, K and Ca uptake. N, K, and Ca content were significantly and positively correlated among each other.

3.7 Correlation of green fodder yield with quality parameters of green fodder

The green fodder yield (GFY) was significantly associated with DM, OM, CP, TA, AIA and NDF (Fig. 6). There was no significant effect of EE, ADF and ADL on GFY. OM and NDF were negatively correlated with GFY. NDF was highly significant and negatively affected by CP. CP was significantly and positively related to TA and AIA. TA was significantly and positively correlated with AIA. TA and AIA had a negative relation with NDF and ADF. ADL was poorly correlated with other quality parameters.

3.8 Principle component analysis

The principal component analysis (PCA) allowed determining which variables better explained the observed differences in fodder maize growth, yield, nutrient content, nutrient uptake and quality due to OSA application. The PCA was carried out with 27 variables, among which 26 were quantitative while OSA concentration was the only qualitative variable (Fig. 7a,b). Two PCs were extracted with eigen values of > 1.0 explained 72.34% of variance (Fig. 7b), first and second components explained 65% and 7.34% variation respectively. Most of the data information was described by principal component 1 (65% loadings) i.e., green fodder yield (t ha^− 1), dry fodder yield (t ha^− 1), N%, K%, Ca%. N, P, K, Ca uptake, leaf: stem ratio, DMA (60 DAS), CGR, RGR at 30–60 DAS, LAI (60 DAS), SPAD (60 DAS), among quality parameters DM%, CP%, TA%, AIA%. These parameters are highly correlated to green and dry fodder yield. In PC 1, OM%, NDF% and ADF% are eigen vectors with negative values (> -0.7) meaning they are negatively correlated and are present in a different plane.

3.9 Economics of fodder maize

Among the treatments with various levels of OSA, RDF (34641.6 ₹ ha^− 1) was having the least cost of cultivation (Table 2). The cost of cultivation increased gradually with increasing concentration of OSA foliar spray. Significantly higher gross return was obtained with the application of 0.25% OSA (83132.0 ₹ ha^− 1) which was statistically at par with 0.30% OSA (82590.8 ₹ ha^− 1), 0.20% OSA (81036.3 ₹ ha^− 1) and 0.15% OSA (77562.3 ₹ ha^− 1). RDF (75153.2 ₹ ha^− 1) was having the minimum gross return among all the treatments. Gross return in 0.25% OSA was 10.6% higher than RDF. The net return due to OSA foliar spray in fodder maize increased significantly, 0.25% (46440.4 ₹ ha^− 1) had the maximum net return of 12.4% higher than RDF (40511.6 ₹ ha^− 1). This treatment was followed by 0.30% OSA with net return of 45524.2 ₹ ha^− 1. B:C ratio based on net return did not vary significantly across the OSA concentration however, 0.25% OSA (1.27) foliar spray had the highest B:C ratio, 1.34% higher over RDF (1.17). 0.25% OSA reported 3.3% higher B:C ratio over 0.30% OSA (1.23) with 2nd highest B:C ratio.

Table 2

Effect of various concentration of ortho silicic acid (OSA%) on fodder maize economics
Treatments	Cost of Cultivation (₹ ha^− 1)	Gross return (₹ ha^− 1)	Net return (₹ ha^− 1)	B:C ratio (based on Net return)	System productivity (t ha^− 1)
RDF	36301.3	158293.9^c	121992.5^b	3.36	9.00^d
0.05%	37026.3	158656.4^c	121630.1^b	3.28	9.00^d
0.10%	37401.3	160718.1^bc	123316.8^ab	3.30	9.14^cd
0.15%	37776.3	166077.6^abc	128301.3^ab	3.40	9.44^bc
0.20%	38151.3	167523.3^abc	129372.0^ab	3.39	9.63^ab
0.25%	38526.3	174163.2^a	135636.9^ab	3.52	9.98^a
0.30%	38901.3	171947.2^ab	133045.9^a	3.42	9.93^a
SEm(±)		2866.4	2866.4	0.08	1.00
MSD(P < 0.05)		12931.6	12931.6	NS	0.44
Note: The pooled mean of two years data followed by the same lowercase letter(s) within a column do not differ significantly at Tukey’s HSD (p < 0.05)

4.1 Growth parameters and yield

The green fodder yield increase due to foliar application of OSA was 7.82–10.61% (Fig. 1a). It was due to an increase in growth and growth rate. The growth and yield of maize were enhanced by silicon fertilization (Pei et al. 2010) and the application of silicon increased the growth attributes (leaf area, chlorophyll content, root length, fresh shoot weight, dry shoot weight), yield attributes (cob length, cob diameter, number of grains and test weight) and yield of maize (Sharma et al. 2013). In a two-year and two-location experiment (Jawahar et al. 2019) on RDF along with soil and foliar application of silicon (Silixol, the same product that is used in the present study) there was increased plant height, leaf area index and dry matter production of maize. The higher values for LAI could be due to increased leaf length, leaf width and a greater number of leaves per plant caused by silicon fertilization. High dry matter content may be due to the maintenance of high photosynthetic activity and efficient utilization of light and translocation of assimilated products to sink. Increased larger leaf area and dry matter of shoot might have accumulated more photosynthates and produced higher biological yield. Similar reports were earlier outlined by (Jawahar et al. 2009) who reported that application of silicon at 100 kg ha^− 1 through fly ash significantly increased plant height, LAI and biological yield of maize. They also recorded higher values for cob length, cob diameter, number of grains cob^− 1, test weight, grain and stover yield in maize. Higher test weight was attributed to better availability and translocation of nutrients as well as photosynthates from source to sink. The adequate silicon supply might have improved the photosynthetic activity, and increased enzyme activity; the increased concentration of soluble substances in xylem enabled the maize plant to accumulate sufficient photosynthates, which resulted in increased dry matter production. These factors coupled with efficient translocation of photosynthates resulted in more number of grains per cob and increased test weight which ultimately led to higher grain and stover yield. In current experiment, the maize was used as fodder but the reasons cited above may well explain high growth parameters, green and dry fodder yield of fodder maize. The positive correlation (Fig. 5) between nutrient content and green fodder yield and principal component analysis (Fig. 7) also explains improved fodder maize yield because the concentration of N, K and Ca were also increased due to OSA (Fig. 1,Fig. 3,Fig. 5).

4.2 Physiology

An interaction between Si and nitrogen and an increase in the levels of chlorophyll a in Oryza sativa plants were reported by (Ávila et al. 2010). The increase in SPAD value which is an indicator of plant greenness could be attributed to increased chlorophyll a content and, consequently, photosynthetic rate. Chlorophyll is an important pigment in photon absorption, transmission, and transportation and is closely related to photosynthesis (Liu et al. 2019). Nitrogen is required for the production of chlorophyll, nucleic acids, and enzymes. Therefore, increased nitrogen content can improve the chlorophyll content in crop leaves, thus improving photosynthetic performance (Bassi et al. 2018). In the current study also nitrogen content was increased due to the foliar spray of Si which may have increased the chlorophyll content and greenness of fodder maize as reflected by SPAD values (Fig. 2b and Fig. 3a). Likewise, an increase in nitrogen content increases RWC (Fig. 2a) in plants which in the present study also shows positive relation with Si foliar spray. The argument is also supported by the contribution of SPAD, RWC and LAI in the principal component 1 to the effect OSA foliar application (Fig. 7). Researchers assume foliar applied OSA is able to pass through the leaf cuticle or stomata into underlying cells. and the mechanism behind the way OSA is able to translocate between cells (through cell walls and intercellular spaces). But further research is needed to prove this assumption and in what ways OSA influences plant physiology.

4.3 Nutrient content and uptake

Interactions of Si fertilization with other plant nutrients including nitrogen have been well documented (Bokor et al. 2017; Greger et al. 2018; Pavlovic et al. 2021). Si positively affects almost all aspects of nitrogen nutrition, including nitrogen uptake, assimilation, and remobilization, and it has been reported in many crops (Pati et al. 2016; Cuong et al. 2017; Pavlovic et al. 2021). Beneficial effects of Si on plant growth and production have been reported under low, optimal, and excessive nitrogen supply (Gou et al. 2020). In oil palm seedlings, nitrogen content was enhanced with the supplementation of Si. The mechanisms underlying the stimulatory effects of Si have not been reported in any plants, but it has been demonstrated that increased nitrogen concentration in plant parts resulted from enhance nitrogen fixation, as well as upregulation of NO₃⁻ transporter genes and genes involved in nitrogen uptake. Another mechanism states that silicon may improve the function and integrity of cell membranes and result in increased nutrient uptake and transport (Zhu et al. 2019). The present study did not witness significant increase in P content in fodder maize may be that silicon does not directly affect the accessibility of P in soil unless plant experience P deficiency stress. Studies have demonstrated that the uptake of phosphorus by plants, both in solution and soil cultures, is not influenced by silicon treatment under optimum P availability (Sahebi et al. 2015). Our experimental soil was high in P content, so the increase recorded due to OSA was not significant. Potassium plays an important role in the regulation of osmotic potential in root tissue, which is necessary for the maintenance of cell turgor pressure, transport of xylem sap, and balancing plant water relations (Liang et al. 2005a, b). Calcium is an important element in maintaining the structure and function of cell membranes in the maintenance of cell wall integrity, selective regulation of ion transport and ion exchange and initiation of signal transduction cascades. Expression of K and Ca transporting gene are influenced by Si application (Liang 1999). Studies show in many plant species, foliar stabilized silicic acid (sSA) applications increase the nutrient uptake as measured by grain and straw yield, the concentrations of N, P, K and Si in the flag leaves (Soratto et al. 2012) and the concentrations of P, Ca and K in young rice plants (Neeru et al. 2019). The concentrations of N, P, K and Ca were enhanced in sSA-sprayed tomato plants (Olle and Schnug 2016). Despite the many positive effects of foliar sSA, the exact mode of action is not understood. Although it has been established that plant leaves and other aboveground parts are capable of absorbing all kinds of chemicals and micronutrients, the uptake/absorption mechanism of monosilicic acid by the leaves has not been established. Another hypothesized reason could be, although silicon is the second largest element present in the soil but due to its presence in the amorphous form, it is not available for plants. Plants absorb silicon from the soil solution in the form of monosilicic acid, also called orthosilicic acid (Lewin and Reimann 1969). In this study, a strong positive correlation and their contribution in principal component 1 (Fig. 5,Fig. 7) was observed between yield and N. K and Ca content and N, P, K and Ca uptake. Therefore, it could be understood that for the above reason foliar application n of Si may have improved the concentration and uptake of essential plant nutrients such as N, K and Ca (Fig. 3,Fig. 4).

4.4 Green fodder quality

As evident from the above discussion that Si application improves the growth, yield and uptake of nutrients by enhancing physiological and biochemical responses of plants, it may be accounted for increase in dry matter content of fodder maize in case of current study (Table 1). The positive response of ortho silicic acid on N content and DM resulted in high crude protein yield. (Sonobe et al. 2010) soluble sugar and amino acid in plants increased due to Si application because of increased water potential and photosynthesis. Leaf contains more protein than stem, high leaf:stem ratio of fodder maize may explain its high CP content. Higher EE in the present study may be because EE and CP are positively related. (Aldal’in 2017) reported, significantly higher crude fat content in maize grain under 100% NPK alone over control might be due to higher fat metabolism associated with higher contents of essential nutrients, better uptake, and synthesis of more glycosides. TA content includes crude silica and mineral nutrients such as P, K, and Ca. Due to the increase in concentration of minerals in fodder maize higher TA content was witnessed. AIA content after wet digestion with HCl, represents the crude silica content (silicon compounds measured collectively as silica), which in our current study was found significantly higher however the silica was not associated significantly with the lignified structures as reflected by no significant change in ADL content. This may be so Si is present associated with Ca pectate in middle lamella (Smith et al. 1971) or silicified cells such as silica cells, silica bodies on bulliform cells or dumb bell silicified cells in vascular bundles (Sahebi et al. 2015). Organic biomolecules with Si primarily polymerizes to form biosilica are a wide range of carbohydrates, proteins, lipids, phenolic compounds and metal ions (Harrison (formerly Perry) 1996; Currie and Perry 2007). Si is known to polymerize with amino acids, like OH^– side groups of serine is involved in H–bond formation with silicic acid Si(OH)₄ (Coradin and Livage 2001). Both amino acids and peptide can interact with silica through electrostatic interactions and H–bonds (Sahebi et al. 2015). In our experiment Si may not have associated with complex carbohydrate such as lignin significantly as evident but may have associated with amino acids or peptide was evident from significant increase in crude protein content. Protein and fibre fractions are known to be inversely related. There was decrease in NDF and ADF concentration in the present study which was confirmed by (Borawska-Jarmułowicz et al. 2022) in their three-year research regarding the beneficial effect of silicon fertilization, independent of weather conditions, on the CP content and on the reduction of CF, NDF and ADF in plants.

4Interpretation of correlation and principal component analysis

The correlation study and principal component analysis indicate a strong positive correlation between green fodder, dry fodder yield and growth characters, nutrient content and uptake and fodder quality attributes while, there was a negative correlation with fibre fractions. The inference that can be drawn based on the primary data and secondary correlation studies is that foliar application of OSA had promisingly influenced yield, nutrient content, nutrient uptake and quality of fodder maize.

Economics

The Economics of crop production is the most important indication to evaluate any production system. Therefore, cost of cultivation, gross return, net return and their relation (B:C ratio) in any production can be necessary to establish the economic feasibility for farmers. Fodder maize maximum cost (COC) was recorded in with 0.30% OSA (Table 2), while highest gross return and net return was achieved in 0.25% OSA. B:C ratio based on net return did not have any significant effect but numerically was highest in case of 0.25% OSA. The variable cost due to foliar spray of OSA (₹1500 litre^− 1) was the reason behind the increased cost of production but was offset by increased yield.

After completion of two years of study, it was concluded that, fodder maize performs well when applied with ortho silicic acid (@ 0.25%) as foliar spray at vegetative and reproductive stage along with recommended dose of fertilizer in terms of better growth, green and dry fodder yield, nutrient content (NK and Ca) and fodder quality. This treatment also proved to be economically sound.

Ethics approval

Not applicable.

Consent to participate

All authors agreed with the concentration and all of them gave explicit consent to submit.

Consent for publication

We have the consent of the authors for the publication.

Availability of data and materials

Supplementary materials are provided

Competing interests

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Funding

The authors received no funding.

Author Contributions

Conceptualization, plan of research and lab facility by Bisworanjita Biswal, Rakesh Kumar, Ashwani Kumar, Rajesh Kumar Meena, Hardev Ram and Arvind Kumar Rai. Field and lab experimentation, observation recording, manuscript writing was done by Bisworanjita Biswal. Assistance in lab analysis by Suryankanta Kashyap. Statistical data analysis by Subhradip Bhatacharjee and Kirttiranjan Baral. Manuscript correction by Rajeswari Das and Smrutirekha Pradhan. Formatting and final drafting by Biswajit Rana and Birbal.

Acknowledgments

The authors wish to acknowledge Director, ICAR–National Dairy Research Institute for and ICAR–Central Soil Salinity Research Institute for providing laboratory and field staff facility for completion of this study. The authors also acknowledge ICAR–National Dairy Research Institute for granting fellowship during the study period.

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Ortho Silicic Acid: A Novel Approach to Enhance Plant Nutrition and Quality in Fodder Maize

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