Silicon Fertilization Research Articles

Soil Drenching with Silicon Improves the Adaptive Response of Tobacco Cultivation under Excess Water Condition

Tobacco variety H382 was a cigar type tobacco that has a high economic value and potential as export trade commodity in Indonesia. The development stage of tobacco was very sensitive to water stress, like the water excess. Silicon was one of the most abundant elements in earth crust and has a role in water stress reduction to the plant. The objective of this study was to determine the response of tobacco crop variety H382 with the application of silicon fertilizer to adapt in waterlogging stress condition. This study used a factorial randomized block design with first factor was silicon fertilizer (0, 0.15, 0.30 and 0.45 ml) and second factor was excess water stress treatments (50% to 70%, 70% to 90%, 90% to 110% and 110% to 130% of field capacity). All treatments were replicated three times. The results showed that the addition of 0.45 ml silicon fertilizer to waterlogged tobacco crop could escalate the adaptive response of plant to cope with stress; seen from the increasing of the opened stomata, aerenchyma formation and the chlorophyll content of tobacco crop under excess water stress compared to control. Silicon supplementation improves the water availability in root surroundings and repairs the root architecture; thus, lead to a better hydraulic conductivity of the root for water and nutrient intake. Furthermore, authors found that the application of silicon fertilizer helped tobacco crop variety H382 improve plant adaptability to deal with excess water stress.

Impacts of Uptake and Accumulation of Cd on Double Rice-Paddy Soil by Silicon Fertilizer Continuous Application

The impacts of silicon (Si) fertilizers on cadmium (Cd) bioavailability in soil and Cd accumulation in paddy-rice plants were investigated in a field positioning test. The results indicated that the continuous application of 180 kg·hm-2 Si fertilizers improved soil bioavailable Si in paddy-rice fields by 108.1%-275.0% and improved pH values by 1.15-1.33 in soil. The difference in the contents of DTPA-Cd in soil by 12.3% and 15.9% was significant in early and late rice, respectively. The continuous application of silicon promoted the transformation of soil cadmium to a stable form and reduced the contents of exchangeable Cd and carbonate binding state Cd in the soil by 2.6%-5.1% and 8.6%-24.9%. The contents of ferric manganese oxide binding state Cd were increased significantly; meanwhile, the contents of organic binding state Cd and residue state Cd in soil were improved by 2.3%-12.8% and 2.3%-6.0%, respectively. The contents of Cd in the root, shoot, and rice were reduced by 38.4%, 49.7%, and 50.9% in early season rice and by 30.6%, 34.4%, and 39.2% in late season rice, respectively. The absorption factors and translocation factors were reduced significantly by 25.5%-49.6% and 13.5%-52.6%, and the average bioaccumulation factors were decreased by 6.0% and 8.0% in early and late season rice. The powder Si fertilizer had the best results overall. In conclusion, Si fertilizer could reduce the absorption and accumulation in rice; however, the continuous Cd reduction effect of continuous application Si fertilizer was not obvious.

Silicon Fertilizer and Microbial Agents Changed the Bacterial Community in the Consecutive Replant Soil of Lilies

Crop replanting leads to soil degradation and soil productivity reduction, which is a challenge for sustainable agricultural development. We previously found that silicon fertilizers combined with additional microbial agents are an effective means to alleviate problems that occur in a variety of Chinese lily during replanting, but little is known about the changes in microbial structure during this process. In the present study, we applied four treatments: CK (control), SF (silicon fertilizer), MF (microbial agents), and SMF (combination of silicon fertilizer and microbial agents). We treated the soil constantly for three years and investigated the bacterial community structure and some specific microbial groups in the soil of the lily root zone using 16S rRNA high-throughput sequencing analysis. The results showed that silicon fertilizer and microbial agent treatment significantly improved the growth status of the plants and changed the diversity and structure of the bacterial community in the soil. The genus Pseudomonas significantly increased in the SF treatment, and the phylum Actinobacteria and the genera Nordella, Devosia, and Rhodoplanes significantly increased in the SMF treatment. The genera Nordella, Pedomicrobium, and Chthoniobacter correlated with the seedling index or available silicon content. In addition, the two genera Gaiella and Nocardioides were the key species linking the bacterial community in the soil. The soil physicochemical properties played an important role in restoring the soil bacterial community structures. In conclusion, silicon fertilizer and microbial agents changed the diversity and structure of the bacterial community. Under the fertilizer supplement model, the enrichment of the phylum Actinobacteria and the genus Pseudomonas played an important role in improving soil health and alleviating CRPs in lilies. In addition, organic matter, available phosphorus, available potassium, and available silicon were found to be the most important factors that have a great impact on the restoration of bacterial community structures.

Silicon Fertilizer – An Imperative Source for Enhancing Yield and Phytolith Content of Maize Hybrid in Desilicated Soil (Typic Rhodustalf)

Silicon is an important beneficial element for improving the photosynthetic efficiency and stress alleviation in crops. Phytoliths are silicon body accumulated in plant parts (plant stone) through bio-mineralization process and there is a significant positive correlation between Si content and phytolith content of crop materials including the leaves, stems and sheaths. A field experiment was focused on the effect of Soil Test Crop Response based fertilizers with silicon sources on growth, yield attributes and phytolith content of Maize hybrid Co 6 at Arasanur, Sivagangai district, Tamil Nadu under Typic Rhodustalf soil during 2021. The results showed that application of Soil Test Crop Response based N, P2O5, K2O + calcium silicate @ 400 kg ha-1 and potassium silicate @ 1% foliar spray at knee high stage (25th Days After Sowing) and vegetative stage (45th Days After Sowing) performed well in enhancing growth and yield attributes viz., Leaf Area Index (5.95), plant height (228 cm), cob length (24.95 cm), number of grains cob-1 (329), grain yield (6.98 t ha-1), silicon content (6.07%) and phytolith content (1.22%), followed by STCR based N, P2O5, K2O + calcium silicate @ 400 kg ha-1+ silicate solubilizing bacteria @ 5 kg ha-1 and both are on par with each other. However, the treatments T10 and T6 performed better in enhancing the growth and yield attributes of maize hybrid Co 6, the maximum Benefit Cost Ratio (2.28) was noticed in T6 (STCR based N, P2O5, K2O + calcium silicate @ 400 kg ha-1 + silicate solubilizing bacteria @ 5 kg ha-1) should be recommended for maize production successfully in laterite soil (Typic Rhodustalf). In future study, it is advisable to conduct further research with different silicon sources on maize under varied soil and climatic conditions.

Silicon fertilization counteracts salinity-induced damages associated with changes in physio-biochemical modulations in spinach

Plant growth and productivity are limited by the severe impact of salt stress on the fundamental physiological processes. Silicon (Si) supplementation is one of the promising techniques to improve the resilience of plants under salt stress. This study deals with the response of exogenous Si applications (0, 2, 4, and 6 mM) on growth, gaseous exchange, ion homeostasis and antioxidant enzyme activities in spinach grown under saline conditions (150 mM NaCl). Salinity stress markedly reduced the growth, physiological, biochemical, water availability, photosynthesis, enzymatic antioxidants, and ionic status in spinach leaves. Salt stress significantly enhanced leaf Na+ contents in spinach plants. Supplementary foliar application of Si (4 mM) alleviated salt toxicity, by modulating the physiological and photosynthetic attributes and decreasing electrolyte leakage, and activities of SOD, POD and CAT. Moreover, Si-induced mitigation of salt stress was due to the depreciation in Na+/K+ ratio, Na+ ion uptake at the surface of spinach roots, and translocation in plant tissues, thereby reducing the Na+ ion accumulation. Foliar applied Si (4 mM) ameliorates ionic toxicity by decreasing Na+ uptake. Overall, the results illustrate that foliar applied Si induced resistance against salinity stress in spinach by regulating the physiology, antioxidant metabolism, and ionic homeostasis. We advocate that exogenous Si supplementation is a practical approach that will allow spinach plants to recover from salt toxicity.

Effect of NPK and silicon fertilizer on growth, flowering, and nectar of Turnera ulmifolia L.

Turnera ulmifolia L. is a beneficial plant mostly planted in the oil palm plantation as it is easily adapting to a variety of environmental conditions, mainly to conserve beneficial insects. Nevertheless, the planted plants were left without proper maintenance and less study was conducted on biological control agent conservation. Thus, this study aimed to examine the effect of NPK, silicon fertilizer and their combination on the growth and development of T. ulmifolia. Treatments including T0 Control (No fertilization application), T1 (0.2 g NPK), T2 (0.2 g NPK+3.9 g silicon), T3 (0.2 g NPK+4.9 g silicon), T4 (3.9 g silicon) and T5 (4.9 g silicon) were applied 20 days after transplanting at monthly interval for three months. Results revealed the greatest height and number of branches were observed in T1. Overall, the chlorophyll content ranged between 27.92 to 31.18 SPAD values. All treatments gave the same effect on morphometric measurements on the first 30 days of observation. After 60 days, the greatest value for broad tube width and length was observed in T4 which differs significantly from other treatments. The application of fertilizer in T1, T2 and T3 showed 10-20% promotive effects over the control in the amount of nectar produced per flower. For all three observation periods, a similar trend was recorded for the total sugar concentration in flowers, where the mean total sugar content was between 1.37 and 1.61 mg per flower.

Effect of silicon fertilization on wheat productivity and profitability in Southern Rajasthan

Area under organic cultivation of wheat (Triticum aestivum L.) is increasing in India. The present two-year study was carried out during 2017–18 and 2018–19 to observe the yield performance of wheat with application of silicon solution (amorphous silica SiO2) under sub-humid conditions of southern plains and Aravalli Hills of Rajasthan. Factorial RBD with five levels of silicon concentration and three growth stages, viz. CRI, tillering and jointing stages were replicated thrice during rabi season of 2017–18 and 2018–19 at Udaipur, Rajasthan, India. Results revealed that application of silicon 8 g/litre water at tillering stage proved significantly superior in enhancing growth characteristics, yield attributes, yield and also gave maximum net returns of 110281/ha and B:C ratio of 2.32

Sustainable and clean utilization of coal gangue: activation and preparation of silicon fertilizer

Coal gangue, a by-product produced during the coal processing, has a serious impact on the environment. Using coal gangue as a fertilizer has been proven helpful in potentially reducing its environmental impact and improving its value. In this study, the formation mechanism and influencing factors of coal-gangue-based silicon fertilizer was studied using XRD and FT-IR measurement technologies. The results showed that the layered structure of coal gangue was severely damaged above 600 ℃, where the kaolin began to transform into metakaolin. When CaCO3 alone was added, CaCO3 mainly played a catalytic role, forming only a small amount of calcium silicate with available-Si content below 12.60%. When corn stalk powder alone was added, the oxides of the corn stalk ash participated in the chemical reaction involving coal gangue, forming nepheline (K(Na, K)3Al4Si4O16) and other silicates with available-Si content of 14.56%. When coal gangue, CaCO3, and corn stalk powder were mixed and calcined, the available-Si content was as high as 22.97% under the synergistic effect of CaCO3 and corn stalk powder; the concentration of toxic metals and ions was below 52.87 mg/kg. The prepared silicon fertilizer can reduce the pollution of coal gangue and meet the agricultural needs of China.

Nutrients, Osmotic and Oxidative Stress Management in Bread Wheat (Triticum aestivum L.) by Exogenously Applied Silicon Fertilization Under Water Deficit Natural Saline Conditions

Nutrients, Osmotic and Oxidative Stress Management in Bread Wheat (Triticum aestivum L.) by Exogenously Applied Silicon Fertilization Under Water Deficit Natural Saline Conditions

Extraction of valuable metals from acidic wastewater and blast furnace slag by a collaborative utilization process

AbstractTwo typical wastes, acidic wastewater and titanium‐bearing blast furnace slag, are generated in the smelting process of vanadium‐titanium magnetite. Generally, the acidic wastewater is neutralized by lime or limestone and titanium‐bearing blast furnace slag is directly stacked in the tailings pond, which not only pollutes the ecological environment but also causes the waste of metal resources. In this study, a collaborative utilization process for efficient extraction of titanium, iron, magnesium, and aluminum from acidic wastewater and low titanium‐bearing blast furnace (LTBBF) slag was proposed. At the leaching temperature of 80°C, the leaching time of 50 min, and the liquid–solid ratio of 9:1, 99.26% Ti, 99.47% Mg, and 99.45% Al could be extracted from LTBBF slag by acidic wastewater. Leaching residue mainly composed of Ca and Si could be used as silicon fertilizer. The Ti in the leaching solution could be separated by adding Na3PO4. The precipitation efficiency of Ti reached 98.53% under the molar ratio of Na3PO4 to TiO2 of 1.4, reaction temperature of 85°C, and reaction time of 40 min. The titanium phosphate ((TiO)2P2O7) was obtained by calcination of the precipitate at 900°C for 3 h. Adding oxalic acid to the filtrate above, the precipitation efficiency of Fe, Mg, and Mn reached 96.47%, 99.21%, and 99.45%, respectively, under the optimal conditions, while the precipitation efficiency of Al was only .38%. By adjusting the pH of the filtrate to 6.5, 99.83% Al could be precipitated as Al(OH)3, and the final solution was evaporated to obtain Na2SO4 products. The method proposed realizes the harmless treatment of acidic wastewater and LTBBF slag and recovers the metal resources in both of them.

Optimization of nitrogen–silicon (N-Si) fertilization for grain yield and lodging resistance of early-season indica fragrant rice under different planting methods

In general, nitrogen (N), silicon (Si), and planting method influence fragrant rice yield and lodging resistance. Nevertheless, the response of fragrant rice yield and lodging resistance to N-Si fertilization under different planting methods has not been examined in detail. Field trials were undertaken in the early seasons of 2018 and 2019. Two Si levels i.e., 0 kg Si h m−2 (Si0) and 150 kg Si h m−2 (Si1), three N levels i.e., 0 kg N h m−2(N0), 150 kg N h m−2(N1), and 220 kg N h m−2(N2) as well as three planting methods i.e., artificial transplanting (AT), mechanical transplanting (MT), and mechanical direct-seeding (MD) were set up for two indica fragrant rice cultivars i.e., ‘Yuxiangyouzhan’ (YX) and ‘Xiangyaxiangzhan’ (XY). Results revealed that the N-Si treatments and planting methods significantly affected the grain yield, lodging index, and some related parameters across the two cultivars. The mean fold change (FC) in grain yield for the different planting methods was ranked MD＞MT＞AT, while MT and MD have larger variation of FC in grain yield and lodging index as compared with AT. Besides, under all planting methods, the N1 and N2 treatments significantly increased grain yield and lodging index, while the Si1 treatment significantly reduced lodging index without affecting grain yield. There were also significant Si and N interaction effects on grain yield and lodging resistance, with the Si1N2 treatment producing the best balance of grain yield and lodging resistance. The treatments differed in grain yield and yield-related traits such as yield components, biomass yield and photosynthetic properties, as well as in lodging index and lodging-related traits such as plant height, N and Si content in the stem sheath, and biomass allocation ratio. Overall, this study revealed that the 150 kg Si h m−2 coupled with 220 kg N h m−2 treatment showed the best positive effects on balancing grain yield and lodging resistance under all planting methods. Additionally, fragrant rice planted by mechanical methods requires more stricter N-Si fertilization because mechanical planting methods produce greater variation in the physio-biochemical characteristics that underlie grain yield formation and lodging resistance.

Silicon fertilization in paddy field

Present study has been done to document the effect of silicon fertilization on various yield parameters of rice (Oryza sativa L.) in land farm under natural environmental conditions. In the current study, the comparison of application of 125 kg/hectare silicon fertilizer + basal fertilizer has been done with control (basal fertilizer without silicon). The significant rise of 88.89% in no. of tillers, 20% in effective tiller, 88.89% in no. of tillers per hill, 92.69% in effective tillers per hill ,4.08% no. of spikes per panicle, 99.16% in total spike in plant, 182.22% in total spikelets per hill, 42.98% in weight of grains/1000, 34.88% number of grain per panicle, 160.65% number of grain per hill, 38.96% grain yield, 30.93% husk yield, 3.41% harvest yield has been observed in crop grown in silicon fertilized soil than control. The results indicates that silicon fertilizer can be used in farm land of rice to increase the yield of paddy.

Dynamic responses of soil enzymes at key growth stages in rice after the in situ remediation of paddy soil contaminated with cadmium and arsenic

The practical application of in situ remediation techniques requires an understanding of the dynamic changes in soil enzyme activity as indicators of soil fertility and health. Experiments were carried out in paddy soils co-contaminated with cadmium (Cd) and arsenic (As) at low (L) and high (H) levels. A calcium and iron (CaFe)-based amendment (limestone + iron powder + silicon fertilizer + calcium‑magnesium-phosphate fertilizer) was applied to the soil at concentrations of 0, 450, and 900 g·m−2 (labeled CK, T1, and T2, respectively), and sampling was conducted at the tillering (TS), booting (BS), filling (FS), and mature (MS) stages. In soil L, urease activity increased significantly by 15.8% under T1 treatment at the MS, catalase activity increased significantly under T2 treatment by 52.4% at the FS and 25.9% at the MS, and acid phosphatase activity increased significantly by 50.1%–65.9% at the TS. For soil H, urease activity increased by maximum values of 101.6% and 28.6% at the FS and MS, respectively. Catalase activity increased by 29.0% at the MS under T2 treatment, and acid phosphatase activity increased by maximum values of 40.5%, 16.0%, and 53.9% at the BS, FS, and MS, respectively. The results indicate that the changes in soil enzyme activity were mainly related to the rice growth stage, soil pH, and available Cd and As after the application of Ca-Fe-based amendment. Overall, at the FS and MS, the amendment increased the soil pH, soil enzyme activity, and cation exchange capacity and reduced the available Cd and As, which reduced the Cd and As contents in brown rice.

Multispectral Analysis of Small Plots Based on Field and Remote Sensing Surveys—A Comparative Evaluation

Remote sensing is an efficient method of monitoring experiments rapidly and by enabling the collection of significantly more detailed data, than using only field measurements, ensuring new possibilities in scientific research. A small plot field experiment was conducted in a randomized block design with winter oat (Avena sativa L.) varieties in Debrecen, Hungary in the 2020/2021 cropping year. Multiple field measurements and aerial surveys were carried out examining the response of oat on Silicon and Sulfur foliar fertilization treatments thereby monitoring their effects on the physiology, production and stress tolerance. Parallel application of in situ (elevation, soil pH, NDVI, SPAD, chlorophyll content) and aerial (NDVI, NDRE) surveys including unmanned aerial vehicles (UAVs) provided a diverse source of data for evaluation. Both the oat varieties (88.9%) and the foliar fertilization treatments (87.5%) were correctly classified and clearly separated with the discriminant analysis based on measured data. The Pearson correlation analysis showed a very strong positive connection (r = 0.895–1.00) between the NDVI values measured using a hand-held system and UAV-installed camera, except the third measurement time, where the correlation was weaker (r = 0.70). Our results indicate that field experiments can be effectively supported by UAVs.

Growth tolerance, concentration, and uptake of heavy metals as ameliorated by silicon application in vegetables

Lead (Pb) and cadmium (Cd) are among the heavy metals with phytotoxic and toxic effects on vegetables resulting in a significant decrease in crop yields. On the contrary, silicon (Si) has beneficial effects in enhancing plants’ tolerance to biotic and abiotic stresses such as that imposed by heavy metals. This study evaluated the effects of Pb and Cd on the growth, biomass, and ameliorative mechanism of Si on concentration and uptake by leafy vegetables: spinach, kale, and amaranth. The greenhouse experiment treatments were Pb, Pb + Si, Cd, Cd + Si, Si, and control. These were arranged as a split-plot in a complete randomized design (CRD): main plots constituted vegetable species and treatments as subplots. The field experiment was carried in the Kenyatta University Research Farm, and treatments included Si application and control, arranged in a randomized complete block design (RCBD). Cadmium application reduced root biomass by 53–70% while Pb reduced it by 54–61% when compared with control. Silicon fertilization enhanced biomass tolerance by three-folds’ and significantly (p < 0.001) reduced concentration and uptake of Pb and Cd. Results indicated a strong negative correlation between Cd concentrations and growth parameters (r = 0.8). The study recommends Si application to enhance leafy vegetables' tolerance to Pb and Cd.

Effect of calcium and silicon fertilization after flowering on pineapple mineral status and flesh translucency

Effect of calcium and silicon fertilization after flowering on pineapple mineral status and flesh translucency

Enhancement of Lodging Resistance and Lignin Content by Application of Organic Carbon and Silicon Fertilization in Brassica napus L.

This study was aimed to investigate the effects of organic carbon and silicon fertilizers on the lodging resistance, yield, and economic performance of rapeseed. Two cultivars, namely Jayou (lodging-resistant) and Chuannongyou (lodging-susceptible), were selected to evaluate the effects of various fertilizer treatments on rapeseed culm morphology, lignin accumulation, and their relationships with their lodging resistance indices. The results showed that both organic carbon and silicon fertilizer applications increased the plant height, basal stem diameter, internode plumpness, and bending strength of rapeseed in both the studied years. The bending strength was significantly and positively correlated with the lodging resistance index and lignin content. It was found that both organic carbon and silicon fertilizers had improved the activities of lignin biosynthesis enzymes (phenylalanine ammonia-lyase, 4-coumarate:CoA ligase, cinnamyl alcohol dehydrogenase, and peroxiredoxins) and their related genes to increase lignin accumulation in the culm, which ultimately improved the lodging resistance. At the same time, the thickness of the stem cortex, vascular bundle area, and xylem area was increased, and the stem strength was improved. The effect of silicon fertilizer was better than that of organic carbon fertilizer, but there was no significant difference with the mixed application of silicon fertilizer and organic carbon fertilizer. Similarly, silicon fertilizer increased the number of pods, significantly increased the yield, and improved the economic benefit, while organic carbon fertilizer had no significant effect on the yield. Therefore, we believe that organic carbon and silicon fertilizer can improve the lodging resistance of rape stems by improving the lignin accumulation and the mechanical tissue structure. Still, the effect of silicon fertilizer is the best. Considering the economic benefits, adding silicon fertilizer can obtain more net income than the mixed application of silicon fertilizer and organic carbon fertilizer.

Organic fertilizers activate soil enzyme activities and promote the recovery of soil beneficial microorganisms after dazomet fumigation

Soil fumigation can reduce the impact of soil-borne diseases, weeds and insect pests on commercial crop production. Unfortunately, fumigation also kills beneficial microorganisms. In this study, we explored if dazomet fumigation could be used in combination with organic fertilizers (silicon fertilizer, potassium humate organic fertilizer, Bacillus microbial fertilizer, and mixtures of the last two) to reduce its impact on soil beneficial microorganisms. We evaluated the effects of adding these fertilizers after fumigation on the soil's physical and chemical properties and its enzyme activities, as well as its effects on the soil microbial communities under continuous production for >20 years. We found that fertilizers applied after fumigation increased the soil nitrate nitrogen content by 11.6%–29.4%, increased available potassium content by 5.6%–26.3% and increased organic matter content by 28.5%–48.8%. In addition, soil conductivity and water content increased significantly by 8.2%–26.5% and 8.0%–16.0%, respectively. The activities of soil catalase and soil sucrase were significantly increased by 6.2%–15.9% and 133.1%–238.5%, respectively. High-throughput DNA sequencing showed that fertilizers applied after fumigation increased the relative abundance of the phyla Proteobacteria, Actinobacteria and Ascomycota; and the genera Sphingomonas, Chaetomium and Mortierella. Silicon fertilizer applied after fumigation has the most significant promotion effect on soil micro-ecological health. The results showed that organic fertilizers applied after fumigation can improve the soil's fertility, activate soil enzyme activities and promote the recovery of soil beneficial microorganisms, which are all factors that improve crop quality and yield.

Beneficial Effects of Silicon Fertilizer on Growth and Physiological Responses in Oil Palm

Vigorous and well-established nursery seedlings are an important component of sustainable oil palm production. We postulated that Si fertilization at the seedling stage could help to achieve improved performance of oil palm seedlings leading to healthy and vigorous nursery establishment. In this study, we evaluated the growth and physiological responses of oil palm Tenera hybrid seedlings under three Si fertilization treatments and a control including (i) 0 g Ca2SiO4 (T0), (ii) 0.5 g Ca2SiO4 (T1), (iii) 3.5 g Ca2SiO4 (T2), and (iv) 7.0 g Ca2SiO4 (T3) per plant per month. Ca2SiO4 was used as the Si fertilizer source and was applied for four consecutive months. Nondestructive data including stem diameter, plant height, leaf length, photosynthetic rate, leaf angle, and leaf thickness and destructive data including leaf, stem, and root fresh weight and dry weight, as well as chlorophyll a, Si, and nitrogen contents, were recorded before treatment (0 DAT), as well as 60 (60 DAT) and 120 days after treatment (120 DAT). Results indicated that Si fertilization enhanced Si accumulation in oil palm seedlings, and maximum accumulation was observed in the aerial parts especially the leaves with the highest accumulation of 0.89 % dry weight at T3. Higher Si accumulation stimulated the growth of seedlings; a total fresh weight of 834.28 g and a total dry weight of 194.34 g were observed at T3. Chlorophyll a content (0.83 gm−2) and net photosynthetic rate (4.98 µM CO2·m−2·s−1) were also observed at T3. Leaf morphology was not significantly influenced under Si fertilization, whereas the nitrogen content of seedlings was significantly increased. Correlation analysis revealed a highly significant and positive association among Si accumulation, chlorophyll a content, photosynthetic rate, total fresh weight, total dry weight, and nitrogen content of seedlings, indicating that Si fertilization enhanced the performance of these attributes. On the basis of the research evidence, it was concluded that Si fertilization should be considered for improved nutrient management for oil palm seedling and nursery production.

Silicon fertilizers, humic acid and their impact on physicochemical properties, availability and distribution of heavy metals in soil and soil aggregates

It has been confirmed that silicon (Si) fertilizer and humic acid (HA) could effectively decrease the heavy metals in soil. Nonetheless, the impact of these additives on soil aggregate characteristics was ignored. Therefore, the effects of Si fertilizer, HA, and their combinations on the physicochemical characteristics, availability of heavy metals (Cu, Cd, Pb, Zn), and fraction changes in soils and soil aggregates were investigated in this research. The results showed that Si fertilizer and HA significantly modified soil properties such as soil pH, electrical conductivity total organic carbon, water-soluble organic carbon, and nitrate‑nitrogen. HA and Si-HA (SHA) supplementation significantly decreased the availability of Cu, Cd, Pd, and Zn. Besides, there was no significant difference in physicochemical properties between soil and soil aggregates. The availability of Cu, Cd, Pd, and Zn in soil aggregates could be significantly inhibited by the addition of HA and SHA, and the content in microaggregates was greater than that in macroaggregates. After the addition of the three additives, the main fractions of heavy metals in different particle sizes were changed and eventually transformed to the residue state. These results indicated that Si fertilizer, HA, and SHA were influential in physicochemical properties and metal availability in soil aggregates. Therefore, it is of great scientific significance to study the impact of heavy metal pollution on the ecological environment in different aggregates, which will provide reference data for future sustainable management of heavy-metal polluted soils.