Nagabovanalli Basavarajappa Prakash

Bacterial wilt of tomato caused by Ralstonia solanacearum severely limits tomato production worldwide. The present study investigated the antibacterial efficacy of six silicon sources against R. solanacearum under in vitro, glasshouse and field conditions, and further confirmed their role in enhancing the biochemical defense responses in tomato plants. Among the silicon sources studied, OSAB and Silixol plus exhibited superior antibacterial activity in vitro, with minimum bacterial growth recorded at 4000 ppm, comparable to antibiotic standard streptocycline @ 500 ppm. Under glasshouse conditions, silicon application significantly reduced wilt incidence, delayed symptom expression and suppressed wilt progression compared with the untreated control. OSAB @ 4 mL L-1 and Silixol plus @ 4 mL L-1 recorded the lowest disease incidence and AUDPC values, achieving up to 73.33% bacterial wilt reduction. Silicon application also enhanced plant growth, biomass accumulation and silicon uptake, with OSAB @ 4 mL L-1 recorded the highest plant height, shoot biomass and silicon content in plant tissue. Field evaluation further confirmed the effectiveness of silicon sources in reducing wilt incidence and rhizosphere population of the pathogen, while significantly improving plant growth and fruit yield. Enhanced resistance in silicon amended plants was associated with elevated activities of defense related enzymes, which peaked at 72 h after treatments. Soil urease and sucrase activities were also significantly enhanced in silicon applied soils. The present study demonstrates that silicon-based sources, particularly OSAB and Silixol plus, effectively suppressed bacterial wilt and enhanced the plant health through direct antibacterial activity and induction of host defense mechanisms.

Applying fertilizers correctly is crucial for enhancing soil fertility and crop productivity. Nonetheless, the long-term effects of slag-based gypsum (SBG) and commercial gypsum (CG) on soil fertility and crop yield remain poorly understood. Field experiments were conducted over six seasons with rice crops to investigate the impact of long-term application of four levels (300, 450, 600, and 750 kg ha⁻¹) of SBG and CG, in conjunction with the recommended dose of fertilizer (RDF), on soil fertility, nutrient uptake, and rice yield. Long-term fertilization with varying levels of SBG and CG significantly influenced the overall rice yield, with the highest grain and straw yields recorded at 750 kg SBG ha⁻¹ (6.90 ± 0.14 and 9.59 ± 0.33 t ha⁻¹, respectively). The application of SBG and CG over the long term had minimal impact on soil pH while notably increasing nutrient uptake and soil fertility. There was a significant correlation between SBG, CG, and soil nutrients, except for soil pH and potassium (K). Principal component analysis (PCA) highlighted that the application of 450, 600, and 750 kg SBG ha⁻¹, as well as 600 and 750 kg CG ha⁻¹, exhibited distinct behavior and outperformed other doses concerning soil nutrients and their uptake. The long-term application of SBG and CG, in combination with RDF, led to an increase in soil fertility and rice yield. However, the long-term application of 450 kg SBG ha⁻¹ yielded comparable results to 600 and 750 kg ha⁻¹ of both SBG and CG, suggesting its efficacy over time.

Phytoliths are composed of 66 to 91% SiO₂ and 1 to 6% organic carbon (C) known as phytolith occluded carbon (PhytOC). PhytOC is critical for long-term C storage in the agroecosystem. A field experiment was carried out to investigate the effect of three different sources of exogenous Si, i.e., diatomaceous earth (DE), silicic acid (SA) and rice husk biochar (RHB) on 1) plant phytolith, C content in phytolith and PhytOC content in different rice organs; 2) relationship between plant phytolith, C content in phytolith, PhytOC content, and soil properties (soil physicochemical properties and readily soluble silicon pools). Different Si sources produced significantly higher phytolith, PhytOC content, and readily soluble Si pools (CCSi, AASi, and ASi) than the control (RDF), with treatment receiving 4 t RHB ha^-1 outperforming the other treatments. Phytolith and PhytOC production were found to be significantly correlated to soil organic carbon (OC), available nitrogen (N) and potassium (K), 0.01 M CaCl₂ extractable Si (CCSi) and amorphous Si (ASi) content in the soil. Redundancy analysis showed that treatments receiving 4 t RHB ha^-1 have a stronger relationship with the CCSi and ASi which majorly contributed to the higher phytolith and PhytOC production. Thus, practices such as Si fertilizers and RHB application have a high potential for phytolith production and PhytOC sequestration, a critical mechanism of the global biogeochemical C sink.

Fall armyworm (FAW) Spodoptera frugiperda is currently being considered as a serious insect pest in maize that causes significant yield losses worldwide. Silicon (Si) and plant growth regulators (PGRs) are known to induce resistance against biotic and abiotic stresses thereby enhancing the yield. This study was conducted to determine the influence of Si and PGRs on the incidence and damage of FAW on maize (Zea mays L.) under field condition. The experiment was conducted in both Kharif and Rabi seasons using a randomized complete block design with three replications and treatments. Various combinations of foliar silicic acid (FSA) and two PGRs such as gibberelic acid (GA₃) and jasmonic acid (JA) were tested to study their effects on FAW incidence and maize yield. The application of FSA at 2mL/plant + GA₃ at 0.5 mg/plant recorded the lowest number of larvae per plant (0.39 larva/plant) with the lowest damage score of 2.55 (Davis scale). The percent infestation was also low for the same treatment, i.e., 34.14 percent infestation with the highest percent reduction over control (56.43%). The highest yield (58.39 q/ha) and cost–benefit ratio (1:2.34) was recorded for FSA at 2 mL/plant + GA₃ at 0.5 mg/plant, which was considered as the best treatment. This study demonstrated that exogenous application of Si along with PGRs has significant negative effect on field incidence of FAW and enhanced the yield of maize.

Background: Slag based gypsum (SBG) is a value-added product of iron and steel industry. Application of gypsum as source of calcium and sulphur for groundnut cultivation is common practice and mainly applied during peg initiation stage of groundnut. However, its effect is mainly influenced by the type of soil and dissolution of gypsum, which facilitates the yield and quality of groundnut. Hence, field experiments were conducted to know the effect of application of different rates of SBG as basal and split application on soil properties, yield, quality, nutrient use and uptake efficiency of groundnut in acidic soil. Methods: This study contains of seven treatments which includes recommended dose of fertilizer (RDF) with three levels of SBG (375, 500 and 625 kg ha-1) was applied as basal and split and 500 kg natural gypsum (NG) ha-1 was applied as basal dose according to package of practice (POP) of University of Agricultural Sciences, Bangalore by using randomly complete block design (RCBD) at Agricultural Research Station, Balajigapade during kharif 2018 and 2019. Result: The pooled data of two field experiments on groundnut revealed that application of RDF + 625 kg SBG ha-1 as 50% at sowing + 50% at peg initiation stage recorded higher pod (28.01 q ha-1), haulm (54.46 q ha-1), kernel (20.59 q ha-1), protein (89.70 q ha-1) and oil (7.06 q ha-1) yield when compared to other treatments. There was an increase in pod, haulm and oil yield of groundnut by 11.62, 20.59 and 17.99%, respectively with the split application of 625 kg SBG ha-1 (50% at sowing + 50% at 30 DAS) over NG applied treatments. Split application of SBG significantly increased the availability of nutrients in post harvest soils than basal application. Significantly higher S and Ca nutrient use efficiency (33.98 and 28.93 kg produce/kg S and Ca utilized, respectively) and uptake efficiency (0.39 and 1.29 kg kg-1, respectively) was recorded with the split application of SBG @ 375 kg ha-1.

Yellow gypsum (YG), a synthetic product from Linz-Donawitz slag containing high iron (Fe) (5.41%), zinc (Zn) (0.37%) and silicon (Si) (3.41%) can be used as a source of these nutrients along with calcium (Ca) and sulphur (S) for groundnut production. Three field experiments were conducted to know the effect of different rates (500 and 625 kg YG ha⁻¹) and time of application (basal alone and basal + split) of YG on growth, yield and economic returns of groundnut, and micronutrient and Si availability and their uptake in comparison with basal application of 500 kg natural gypsum (NG) ha⁻¹. Basal alone and basal + split application of YG significantly increased the growth, yield and economic returns of groundnut. Further, it increased the soil pH, availability of micronutrients, Si and their uptake by haulm and kernel of groundnut over NG. Irrespective of the location, YG application recorded higher plant available nutrient (PAN) coefficient of micronutrients, while NG application recorded higher PAN recovery coefficient of Si. Basal + split application of YG resulted in better growth and yield of groundnut than basal application of YG. In conclusion, YG can be a potential alternative for NG as a source of Fe, Zn and Si along with Ca and S for groundnut production.

The foliar nutrition of silicic acid is considered to be a novel approach in enhancing the performance of many crops worldwide. The present study aimed to assess if the foliar application of silicon (Si) could influence the performance of soybean varieties with distinct crop duration, MAUS-2 (long duration) and KBS-23 (short duration). Field experiments were conducted in two consecutive years (2016 and 2017) of varied rainfall with foliar application of silicic acid @ 2 and 4 mL L⁻¹ for three and two sprays each. The results showed significant enhancement in the yield, seed quality (protein and oil content), and uptake of nutrients (N, P, K, Ca, Mg, S, and Si) by various parts viz., seed, husk, and haulm of both varieties with foliar nutrition of silicic acid. However, the short duration variety, KBS-23, responded well under low rainfall conditions (2016) with two sprays of foliar silicic acid @ 4 mL L⁻¹ and MAUS-2 variety in the second season under higher rainfall (2017) with three sprays of foliar silicic acid @ 2 mL L⁻¹, along with the recommended dose of fertilizer. This research revealed that the effectiveness of foliar silicic acid nutrition differs with the duration of the varieties, number of sprays given, and water availability in the soil during the cropping period.