Boron applied via stipe in dwarf-green coconut: leaf boron content, yield, and xylem tissue morphology

ABSTRACT

Dwarf-green coconut palms are cultivated in sandy soils, such as in the state of Sergipe in northeastern Brazil, and boron (B) deficiency has limited their yield. The recommended corrective measures are B applications to the soil or to the leaf axil. Boron application via the stipe may represent a viable alternative. However, it is necessary to quantify appropriate doses and determine which B sources can be used without damaging the xylem tissues. The objective of this study was to evaluate leaf B contents in dwarf-green coconut palms and their yield as a function of B application via stipe and soil, to establish critical foliar levels, and to assess the morphological integrity of internal vascular tissues, as well as the pH and electrical conductivity of the sap, when B was applied via stipe. Five doses of B complexed with monoethanolamine (2, 4, 6, 8, and 10 g plant^-1 yr^-1) were evaluated after six applications at four-month intervals from July 2021 to March 2023 across the 2021/2022 and 2022/2023 growing seasons. The experimental design was a randomized block in a factorial scheme [(5×2)+1], with four replications, totaling 44 experimental units. Leaf B content in the diagnostic leaf was determined at 15, 30, 60, 90, and 120 days after B application. Fruit yield was measured over two consecutive growing seasons, and the critical foliar B level, sap pH, and sap electrical conductivity were determined. A morphological evaluation of xylem vascular tissues was also performed. Application of B via stipe increased leaf B content and fruit productivity by 80 and 34 %, respectively, while soil application increased by 20 and 19 %, respectively. Furthermore, productivity increased by 10.5 % when B was applied via stipe compared to soil application. Stipe application at 8 g plant^-1 yr^-1, divided into three doses, resulted in a yield of 327 fruits plant^-1 yr^-1. Critical foliar B level was approximately 34 mg kg^-1 when B was applied via stipe, and approximately 23 mg kg^-1 when B was applied via soil. Stipe application of complexed B sources at high doses, such as 10 g plant^-1 yr^-1, induced necrosis of internal tissues in the coconut palm, indicating the need to develop coconut-specific nutritional solutions for stipe application of complexed B.

Keywords
Cocos nucifera L.; boron nutrition; critical B levels; sap pH and electrical conductivity

INTRODUCTION

Coconut palm (Cocos nucifera L.) is a crop of considerable socioeconomic importance, with the giant and dwarf-green varieties cultivated for copra and its derivatives and for fresh consumption, respectively. The Northeast region accounts for 80.9 % of the harvested coconut area and 73.5 % of Brazilian production, with the state of Sergipe being a major producer, responsible for approximately 155,000 tons of fruit (Emdagro, 2025). However, yield in Sergipe remains low, even considering the ongoing replacement of the giant variety with the dwarf-green variety. This low yield has been largely constrained by nutritional factors arising from the naturally low fertility of the soils where coconut palms are most widely grown, such as the sandy soils of Sergipe and, more broadly, across northeastern Brazil (Sobral et al., 2023).

Low fertility of these sandy soils is associated with boron (B) deficiency and represents one of the most limiting nutritional factors for increasing coconut yield (Sobral et al., 2023). Boron deficiency in coconut palms impairs the formation of meristematic tissues in roots and shoots as well as reproductive structures, negatively affecting flowering, fruit set, and yield (Nair, 2021).

Recommended corrective measures include application of B to the soil (Sobral et al., 2023) or to the leaf axil (Pinho et al., 2008). Soil application increases losses of this nutrient by leaching (Ahmad et al., 2012), because in the pH range within which coconut is cultivated, the predominant form of B in the soil solution is H₃BO₃ (the undissociated neutral form), which can migrate down the soil profile to depths beyond root reach (Prado, 2021), particularly in sandy soils during rainy periods (Lindolfo et al., 2020). Consequently, larger amounts of B are required to offset leaching losses, which in these sandy soils can reach up to 70 % of the applied dose (Abreu et al., 2015). Conversely, borate fertilizer applied to the leaf axil benefits only young plants; once the crop is in the production phase, this application method is operationally unfeasible due to the tall stature of the plants.

Therefore, a new method of B application that improves nutrient-use efficiency is essential to increase yield in coconut palms. Endotherapy is a technique that applies phytosanitary products directly into the xylem, allowing their translocation through the plant's conducting vessels (Moura et al., 2023). To date, its use has been largely limited to phytosanitary management (Ferreira et al., 2023, 2024). The use of endotherapy as a means of supplying nutrients is still in its infancy but is promising to improve nutrient-use efficiency - for example, for B in coconut palms.

Some studies have reported increases in leaf B and Fe contents in date palm and peach when B was applied via stipe (Luaces et al., 2015; El-Deen et al., 2018). However, studies on the application of B to stipes in coconut palms have not yet been reported. Broschat and Doccola (2010) evaluated manganese (Mn) applied via stipe in coconut palms and found that this method was the most effective at increasing leaf Mn contents, although they observed necrosis in xylem tissues. Therefore, despite its promise, stipe application of B must be evaluated for potential damage to the conductive tissues of the coconut palm. Ferreira et al. (2024) also reported necrosis of internal tissues following stipe application of insecticides and fungicides in coconut palms. Nonetheless, the potential side effects of stipe-applied B, particularly damage to internal tissues, must be carefully considered and assessed. It is noteworthy that studies on the stipe application of B in coconut palms have not yet been reported in the literature; therefore, this trial was prospective.

The hypothesis of this study is that stipe application of B increases leaf B contents in dwarf-green coconut palms more than soil application, due to greater efficiency in nutrient transport absorption and more rapid assimilation, thereby increasing fruit yield. However, stipe application may be harmful to xylem vessels depending on the applied dose and the chemical characteristics of the product (e.g., pH and electrical conductivity). This study aimed to evaluate leaf B contents in dwarf-green coconut palms and their yield as a function of B application via stipe and soil, to establish critical foliar levels, and to assess the morphological integrity of internal vascular tissues, as well as the pH and electrical conductivity of the sap, when B was applied via stipe.

MATERIALS AND METHODS

Study area

The experiment was conducted on a 1.25 ha section of a commercial dwarf-green coconut plantation covering 10.65 ha at a farm located in the municipality of Neópolis, Sergipe State, Brazil, at coordinates 10° 18’ 36.876” S, 36° 38’ 13.346” W and an altitude of 75 m. The area has been cultivated with dwarf-green coconut palms for 26 years, and minor management practices, mainly fertilization, are carried out according to soil and leaf analysis. The regional climate is classified as type As according to Köppen classification system (Dubreuil et al., 2019). Mean annual rainfall during the 2021/2022 and 2022/2023 growing seasons was approximately 1,200 mm, with precipitation concentrated between May and July, measured using a rain gauge installed on the farm (Figure 1). The mean temperature was 25 °C, as reported by Cintra et al. (2009).

Figure 1
Average monthly rainfall in the production years of the dwarf-green coconut palm, indicating the months in which boron was applied via stipe and via soil at doses of 2, 4, 6, 8 and 10 g plant^-1 yr^-1: (a) 2021; (b) 2022; and (c) 2023. The doses were divided into six applications across the 2021/2022 and 2022/2023 growing seasons, with four-month intervals between applications. Rainfall was measured using a rain gauge installed on the farm where the experiment was conducted.

The soil of the experimental area is classified as Neossolo Quartzarênico (Santos et al., 2025), corresponding to Arenosol according to WRB (IUSS, 2015) and Quartzipsamment according to Soil Taxonomy (Soil Survey Staff, 2022). Chemical and physical soil properties were determined from ten single samples collected randomly in a zigzag pattern across the experimental coconut field at the layers of 0.00–0.20 and 0.20–0.40 m. After homogenization, the samples were combined into a composite sample (Table 1).

Table 1
Chemical characterization and particle size analysis of the soil before the establishment of the agronomic experiment

Layer	pH(H2O)	P (Mehlich)	P (Resin)	S-SO42-	Ca2+	Mg2+	K+	Na+	SB(1)	Al3+	(H+Al)	CEC(2)
m		–––––––––– mg dm-3 ––––––––––			–––––––––––––––––––– cmolc dm-3 ––––––––––––––––––––
0.00-0.20	6.49	578.75	63.05	6.60	3.32	0.67	0.24	0.22	4.45	0.00	0.53	4.96
0.20-0.40	6.58	173.45	59.00	4.70	1.86	0.42	0.27	0.14	2.69	0.00	0.32	3.02
	Fe	Mn	Cu	Zn	B	m(3)	V(4)		Sand	Silt	Clay
	–––––––––––––––––––– mg dm-³ ––––––––––––––––––––					–––––– % –––––– –––––– g kg-1 ––––––
0.00-0.20	22.90	31.95	1.95	30.05	0.82	0.00	89.3		916	24	60
0.20-0.40	26.35	3.30	0.52	5.65	0.76	0.00	88.9		906	15	79

• ⁽¹⁾
  Sum of bases;
• ⁽²⁾
  Cation exchange capacity;
• ⁽³⁾
  Al saturation;
• ⁽⁴⁾
  Bases saturation.

Fertigation, phytosanitary, and nutritional management

The irrigation system adopted on the farm was microsprinkler irrigation, with two emitters per plant, positioned 1.0 m from the coconut palm stipe on opposite sides, and an average flow rate of 33 L h^-1. Mean water consumption during the experimental period, considering crop water demand and the current yield of the farm, was approximately 260 L plant^-1 day^-1. Irrigation depth was calculated based on this mean consumption and adjusted according to rainfall.

Fertilization was carried out based on soil analysis (Table 1). The following nutrients and annual doses per plant were applied: 3.96 kg N; 5.10 kg K; 0.400 kg Mg; 0.413 kg S; 0.185 kg Zn; 0.100 kg Cu; and 0.288 kg Mn. These nutrient amounts were supplied via fertigation three times per week, totaling 12 applications per month. Fertilizer sources used were: N (urea, ammonium sulfate, and MAP); K (KCl); P (MAP); S (ammonium sulfate and magnesium sulfate); Mg (magnesium sulfate); Zn (zinc sulfate); Mn (manganese sulfate); and Cu (copper sulfate).

Phytosanitary management was performed through constant monitoring of the plants, including control of leaf spot and the coconut necrosis mite. For this purpose, difenoconazole (Score^®; 10 mL plant^-1) and abamectin (Vertimec 18 EC; 5 mL plant^-1) were applied, respectively. To capture Rhynchophorus palmarum, attractive baits containing pheromone, sugarcane rolls, and molasses were used.

Treatments and experimental design

The experimental design was a randomized block in a factorial scheme [(5×2)+1], with four replications, totaling 44 experimental units. Each experimental unit consisted of eight plants arranged in an equilateral‑triangle planting system with spacing of 7.5 × 7.5 × 7.5 m, corresponding to 205 plants ha^-1. Treatments comprised five doses of B (2, 4, 6, 8, and 10 g plant^-1 yr^-1) supplied as a commercial product with B complexed by monoethanolamine (MEA) (4 % N; 10.9 % B), applied via stipe and via soil, together with an additional control treatment without B application. Another additional control was used, consisting of a single dose of 5 g plant^-1 yr^-1 of boric acid, only to evaluate the effect of successive MEA applications in the 2021/2022 and 2022/2023 growing seasons on xylem tissues, because boric acid has an acidic pH and MEA has an alkaline pH. The dose of boric acid used was only 5 g plant^-1 yr^-1 because higher doses require large dilutions due to the low solubility of boric acid. In this case, the factorial scheme was [(5x2)+2].

The MEA is widely used as a complexing agent for minerals such as B, forming a stable and highly water‑soluble complex (Liakopoulos et al., 2009). Boron complexed with MEA was selected because the solubility of boric acid and borax - the main conventional B sources - is low, which would require large volumes of water for dilution and render stipe application impractical. The standard recommended dose for soil application of B is 5 g plant^-1 (Sobral et al., 2008).

Accordingly, two doses below and two doses above the standard recommendation were defined, considering that stipe application typically results in faster B assimilation than soil application and that the thresholds between deficiency and toxicity are very narrow (Jokanović, 2020). The commercial product used as the B source contained approximately the same B content (10.9 % B) as borax (10 % B), which is widely used and recommended for soil fertilization of dwarf-green coconut in Brazil (Sobral et al., 2009).

Boron application

For stipe application, coconut palms were drilled with an impact drill at approximately 0.40 m above the soil surface, at a 45° angle. A catheter (9 cm × 2 cm) was then installed (Figure 2), and B doses were administered using a 60 mL syringe graduated in 2 mL increments (Figure 3a).

Figure 2
Installation of the catheter in the stipe of the dwarf-green coconut palm. The catheter installation consists of drilling a hole using a drill bit with a diameter sufficient to create a 2.0 cm hole and a depth of 9.0 cm. The hole should be drilled approximately 0.40 m from the ground at an angle of about 45°, where the catheter is inserted with the aid of a guide of the same diameter and subsequently capped with an appropriate cap. The hole is approximately 0.12 m deep. Only one hole per plant is necessary. For more details, please visit: https://1drv.ms/v/c/4349a8e3f67972fa/IQAzc1vXJUDMTK8Yr1Ct-uHjARnPXIyBworUU4QvVzqtLmw?e=KMG4gC

Figure 3
Application of B fertilizer in dwarf-green coconut palm via stipe (a), sap collection (b), and morphological evaluation of xylem tissues using an endoscope (c). The endoscopic inspection camera was introduced through the same catheter orifice, with a 7 mm diameter probe, 0.20 m length, LED illumination, 640 × 480 resolution (VGA), and Android/PC compatibility. The endoscope was inserted to the limit of the orifice to assess possible morphological damage to the xylem tissues after the application of boron complexed with monoethanolamine (MEA).

Boron solutions for stipe application were prepared at a 2:1 dilution (water:product) and split into six applications four-month intervals from July 2021 to March 2023 across the 2021/2022 and 2022/2023 growing seasons [(July and November 2021); (March and July 2022); (November 2022 and March 2023)] (Figure 1). The two years of dwarf-green coconut cultivation spanned 2021–2023 because B applications began in July 2021 and were completed in March 2023. At each application, one-third of the dose was applied, so the full dose was completed only after the third application.

Application of 1/3 of each dose of B using MEA in a 2:1 dilution (water:MEA) corresponded to a total applied volume of 18.4, 36.8, 55.2, 73.4, and 91.8 mL. The catheter's intake capacity was only 60 mL; therefore, volumes exceeding this capacity were divided into two applications at 6:00 AM and 2:00 PM. After application, the catheters were properly capped with appropriate caps.

Soil-applied B doses were diluted in 1 L of water and applied to the projected plant crown in three applications (six in total across the 2021/2022 and 2022/2023 growing seasons), with four-month intervals between applications and at the same time points as stipe application. The fertilizer was distributed in the soil within the canopy projection, at a distance of 0.50 m from the stipe, covering a radius of up to 1.5 m. The diluted fertilizer was applied using a backpack sprayer.

The dilution used for soil application was greater than for stipe application to enable distribution over the crown area. Had the stipe dilutions followed the same pattern as the soil dilutions, the time required to administer the fertilizer via stipe would have been excessively prolonged, rendering that application method impractical.

Leaf B content

Leaf samples for determination of B contents were collected at 0 (control), 15, 30, 60, 90, and 120 days after each B application. Sampling consisted of eight leaflets per plant, four from each side of the central portion of the diagnostic leaf (leaf 14), using the central 0.10 m of the leaflets (Saldanha et al., 2015). After removal of the midrib, leaflets were dried in a forced-air oven at 75 °C, ground, mineralized, and analyzed for B content (Gavalak et al., 2005). Boron levels were evaluated at 15 days only in the first B application period; in subsequent periods, B content was evaluated at 30 days after application. Sampling periods for leaf B content across the 2021/2022 and 2022/2023 seasons were: August-November 2021; December 2021-March 2022; April-July 2022; August-November 2022; December 2022-March 2023; and April-July 2023. Therefore, when assessing variation in leaf B content as a function of applied doses, means were calculated from data obtained in comparable periods across the two seasons.

Increase in leaf B content following stipe application

The increment in B content in the diagnostic leaf was calculated as the difference between the B content measured in treated plants and that measured in the control (no B application). This calculation was performed for each stipe-applied B dose at 30 days after application, considering only the first application period in the two growing seasons (2021/2022 and 2022/2023). This approach allowed assessment of the increment behavior across two consecutive seasons to evaluate its sustainability.

Concurrently, boric acid was applied as a single dose of 5 g plant^-1 as a B source to evaluate whether the higher pH and electrical conductivity of the MEA-complexed B product, compared with the lower pH of boric acid (closer to sap pH), could cause damage to internal palm tissues and thereby reduce the effectiveness of repeated stipe applications of the MEA source.

Sap pH and electrical conductivity

Sap was collected using a syringe attached to tubing (Figure 3b) at 30 days after each stipe application of B. Sap was also sampled from the control treatment (no B application). The pH and electrical conductivity were measured with a calibrated pH meter and a conductivity meter, respectively. Measurements were recorded immediately after collection to avoid changes due to exposure.

Morphological assessment of vascular tissues

The internal vascular tissues were examined by endoscopy at 30 days after each stipe application of B (Figure 3c). Endoscopic images and observations were recorded to document any structural alterations associated with the treatments; findings were described qualitatively and, where applicable, quantified for comparison among treatments.

Data analysis

Leaf B content

Boron content data from the diagnostic leaf were subjected to the Shapiro–Wilk test for normality (Shapiro and Wilk, 1965) and Cochran test for homoscedasticity (Cochran and Cox, 1957). After verification of normality and homoscedasticity, leaf B contents were analyzed by two complementary approaches:

1. Repeated measures over time - When considering repeated measurements, multiple regression was performed with dose and time as explanatory variables within each application method (stipe and soil). Response surfaces were generated for each application method, and cross‑sections of these surfaces were examined to evaluate dose × time interactions. These analyses used data from each B assessment period, with values averaged across comparable sampling intervals from the two growing seasons (2021/2022 and 2022/2023).

2. Dose effect irrespective of sampling time - When B content was analyzed as a function of applied dose regardless of sampling time, the value for each dose corresponded to the mean of contents measured at the different sampling times and to the mean of comparable periods across the two seasons (2021/2022 and 2022/2023). The regression equation obtained from this analysis was used to estimate the critical B level for each period of the year, considering the average of the two seasons.

The best regression model explaining the data was selected by applying a t-test (p<0.05) to the model parameters, selecting the model with the highest and most significant coefficients. This procedure was performed for all regressions, whether multiple or simple.

The data on B levels as a function of the doses of B applied via stipe and via soil were grouped in the same graph, and the B levels obtained for each dose applied via stipe and via soil were compared using the F test (p<0.05), showing the dose at which there was a difference between B applied via stipe and applied via soil.

Critical leaf B level

Dwarf-green coconut yield was assessed monthly over two cultivation years corresponding to August 2021-July 2022 (first measurement) and August 2022-July 2023 (second measurement). Yield was expressed as the number of fruits per plant per year (fruits plant^-1 yr^-1). Mean yield values for the two cultivation years were plotted as a function of the B doses applied via stipe and via soil. Using the fitted regression equations, the maximum points for each equation were determined, representing the B dose that produced the maximum yield for dwarf-green coconut under stipe and soil application.

Critical leaf B levels were determined for each post‑application assessment period for both stipe and soil applications. Accordingly, mean B contents measured in the diagnostic leaf during each assessment period in the two seasons (2021/2022 and 2022/2023) were plotted against the corresponding B doses applied via stipe and via soil, and regression equations were obtained. The critical leaf B level for each period was then estimated by substituting the dose associated with maximum yield into the respective regression equation. The association between the critical level of B in the leaf and the dose that provided maximum fruit production was because this dose represents maximum agronomic efficiency, while the dose associated with 90-95 % of maximum production has a direct relationship with economic processes characterized by high market variability. Annual critical leaf B levels were calculated as the mean of the values obtained for the three evaluated periods across the two cultivation seasons.

ANOVA was performed on the critical level data obtained for each evaluation period and for the two application methods (stipe and soil), with application method and evaluation period treated as fixed main effects and their interaction included in the model. The F test was used to assess significance at p<0.05; when main effects and/or their interaction were significant, mean comparisons were performed using the Tukey test at p<0.05.

Increment in leaf B content following stipe application

ANOVA was conducted on the increments in leaf B content measured 30 days after each applied dose, expressed relative to the control and including data from both cultivation seasons. Dose and cultivation season were included as main effects together with their interaction. The F test was applied at p<0.05; when effects and/or their interaction were significant, pairwise comparisons were made using the Tukey test at p<0.05.

Sap pH and electrical conductivity

Sap pH and electrical conductivity were plotted as a function of applied B dose and fitted with simple regression models to evaluate the response of these chemical indicators to increasing B rates. Model parameters were tested using a t test (p<0.05); the model with statistically significant parameter estimates and the largest explanatory power was selected as the best descriptor of the data.

RESULTS AND DISCUSSION

Effect of dose, form, and time of application of B on leaf B content

The B doses applied via stipe and via soil, and the time required for these doses to affect leaf B content, exhibited distinct patterns across all evaluation periods (Figures 4, 5, and 6). In the first application period, stipe application produced a linear dose response: leaf B content increased with increasing B dose, except at 120 days after application (Figure 4a1). In contrast, B content varied quadratically with time (Figure 4a2). Increases of 44.90, 38.45, 24.19, and 12.65 mg kg^-1 in leaf B content were observed at 15, 30, 60 and 90 days, respectively, after application of the highest dose of B compared to the control (Figure 4a2). These results indicate that stipe application is an effective method for B nutrition of dwarf-green coconut, consistent with reports on endotherapy for phytosanitary products (Moura et al., 2023) and with stipe application of Mn in coconut (Broschat and Doccola, 2010).

Figure 4
Response surface of B content in dwarf-green coconut palm leaves as a function of B doses applied via stipe (a) and via soil (b) in the first application period, as well as the effect of cross-sections on this response surface, showing the behavior of B content as a function of the dose applied via stipe (a1) and via soil (b1) and of the time (a2) and (b2). These data represent the average of the 2021/2022 and 2022/2023 growing seasons. D represents the doses of B; T represents the time after application of these doses.

Figure 5
Response surface of B content in dwarf-green coconut palm leaves as a function of B doses applied via stipe (a) and via soil (b) in the second application period, as well as the effect of cross-sections on this response surface, showing the behavior of B content as a function of the dose applied via stipe (a1) and via soil (b1) and of the time (a2 and b2). These data represent the average of the 2021/2022 and 2022/2023 growing seasons. D represents the doses of B; T represents the time after application of these doses.

Figure 6
Response surface of B content in dwarf-green coconut palm leaves (a) as a function of B doses (a1) and time (a2), when B was applied via stipe in the third application period, as well as the effect of cross-sections on this response surface, showing the behavior of B content as a function of the dose applied and of the time. These data represent the average of the 2021/2022 and 2022/2023 growing seasons. D: doses of B; T: time after application of these doses.

The maximum leaf B contents observed at the highest dose did not produce visible toxicity symptoms. It should be noted that, in this study, only one-third of the annual dose was applied in the first application period; the remaining two-thirds were applied in two subsequent periods (i.e., each application delivered one-third of the annual dose). Broschat and Doccola (2010) showed that, at 30 days, the application of Mn via stipe in coconut trees at small doses (2 g plant^-1) resulted in increases of more than 64.77 % (75.4 mg kg^-1) in the levels of this nutrient in the leaf. However, as already reported, in our study, only 1/3 of the doses were applied in the first period of B application.

After 90 days, there was only a slight increase in B content in the leaves (Figure 4a2). However, this B may have come from the soil, due to climatic conditions (reduced rainfall; Figure 1), with a consequent increase in transpiration, because this favors transpiration flow, as well as mass flow and, consequently, greater absorption of B available in the soil, promoting its transport to the aerial part (Chu et al., 2025). At 120 days, leaf B contents stabilized at approximately 25 mg kg^-1, indicating no persistent residual effect of the initial stipe application (Figure 4a2). Accordingly, reapplication at or before 120 days is recommended to prevent leaf B from declining to levels that could compromise nutritional status. Fractionating stipe applications every 4 months (3 applications per year) proved appropriate.

When the application was made via soil, the B content in the leaves also increased linearly with increasing B doses (Figure 4b1), but showed a quadratic effect over time (Figure 4b2). Increases of 2.65, 3.14, 4.15, 5.18 and 6.20 mg kg^-1 in leaf B content were observed at 15, 30, 60, 90, and 120 days, respectively, after application of the highest dose of B compared to the control (Figure 4b2). Broschat and Doccola (2010) showed that the application of Mn to coconut trees via soil with high doses (192 g plant^-1) at 30 days resulted in increases of 29.3 mg kg^-1 in the levels of this nutrient in the leaves. In our study, the B gain was about 10 times lower, whereas the authors used a dose about 58 times higher (3.33 g plant^-1 in the first application period). Thus, the increase in B content in the leaf as a function of increasing doses of B applied via soil was small.

Doses of B applied via soil were only sufficient to raise the B content in the leaf to around the critical level reported in the literature, which is around 20 mg kg^-1 for yields between 200 and 250 fruits plant^-1 yr^-1 (Santos et al., 2004; Sobral et al., 2009). However, for yields greater than 300 fruits plant^-1 yr^-1, the critical level is 39 mg kg^-1 (Santos, 2020). This indicated that the doses of B applied to the soil were insufficient to increase leaf B levels and achieve the recommended value, which promotes an adequate nutritional status, especially for high coconut yields.

Gains in leaf B content following soil application were smaller than those observed after stipe application during the first application period. However, soil-derived gains were progressive over time, whereas gains from stipe application declined (Figure 4). It was also found that, at 120 days, regardless of soil or stipe application, the B content in the leaf was, on average, 28.35 mg kg^-1 (Figures 4a and 4b).

When evaluating the second application period, it was observed that there was also interaction between the doses applied and the time it took for these doses to exert their effects on the B content in the leaf, with a linear increase in B content in the leaf when B doses via stipe were increased and a reduction in content gains over time (Figure 5a). Increases of 37.9, 26.53, and 15.17 mg kg^-1 in leaf B content were observed at 30, 60, and 90 days, respectively, after application of the highest dose of B compared to the control (Figure 5a2). These gains in B content in the leaf are slightly higher when compared with the first fertilization period (25 to 26.5 mg kg^-1, on average) (Figures 4a2 and 5a2), which can be justified by the time of application, because the second period was the driest time of the year for B application, both in the 2021/2022 growing season and in the 2022/2023 growing season (Figure 1).

Concomitantly, a 20 % reduction was observed between 30 and 60 days at the highest dose used in this second period of B application (58.05 to 46.44 mg kg^-1) (Figure 5a2). However, a smaller reduction was expected in this period compared with the first period, in which the reduction was around 30 % (54.02 to 37.94 mg kg^-1) (Figure 4a2), given that after fertilization in the xylem in this second period, sunny days with high transpiration rates favored faster nutrient absorption by the plant, combined with greater demand in physiological processes (Luaces et al., 2020). At 120 days, B levels stabilized at 19.41, 20.17, 20.93, 21.69, 22.45, and 23.17 mg kg^-1 (Figure 5a2). In this second application period, contrary to what occurred between 30 and 60 days, a reduction in B content in the leaves of approximately 34 % was observed between 90 and 120 days at the highest dose used (Figure 5a2), which was higher than that observed in the first application period (~16 %) (Figure 4a2), due to climatic conditions, because there was a considerable increase in rainfall 120 days after the application of B in this second period (Figure 1), which reduced the absorption of available B from the soil (Wimmer and Eichert, 2013; Karthika et al., 2018).

Conversely, when B was applied via soil, there were increases of 11.42, 7.91, and 4.39 mg kg^-1 in leaf B content at 30, 60 and 90 days, respectively, after application of the highest dose of B compared with the control (Figure 5b2). At 120 days, the B contents in the leaf were 21.22, 19.94, 19.39, 19.57, 20.46, and 22.09 mg kg^-1 in plants fertilized with doses of 0, 2, 4, 6, 8, and 10 g plant^-1, respectively, showing a stabilization of B levels, without influence from the applied doses (Figure 5b2). This result revealed a difference in B gain between the first (Figure 4b2) and second application periods (Figure 5b2), with higher increases in leaf B content in the second period, which can be justified by the fact that this was a much drier period than the first period (Figure 1), allowing greater use of the B applied to the soil via fertigation due to the higher transpiration rate (Karthika et al., 2018). These results revealed that the application of B via soil depends on the season in which it is applied, that is, on whether rainfall is higher or lower during the application period.

The increase in B levels due to B application in this second period was greater than in the first for both application methods (Figures 4 and 5). This application period was the driest of the year in both the 2021/2022 and 2022/2023 growing seasons (Figure 1). Therefore, this drier period increased transpiration, favoring B translocation via the xylem (Abreu-Junior et al., 2025). In irrigated dwarf-green coconut cultivation, soil moisture is constantly monitored; consequently, B transport by mass flow in the soil occurs naturally, with transpiration flow being the main factor determining B translocation through the xylem. Therefore, high temperatures, combined with high transpiration rates during the drier period of B application, favored increased B levels in coconut leaves. This effect was more evident when B was applied via the soil, because in wetter periods, leaching becomes a determining factor for this application method, especially in sandier soils (Sarkis et al., 2024). Conversely, the data showed that the period with the highest B content in the leaf due to B application via the xylem was the second, and therefore the driest, period. Boron application via xylem also depends on high transpiration flow; that is, it is a much more efficient technique for applying B than via soil, at any time of the year.

During the third application period, there was also interaction between the application methods, the doses of B applied, and the time it took for these doses to exert their effects on the B content in the leaf, with an increase in B content in the leaf when the doses of B via stipe were increased and a reduction in content over time (Figure 6). Increases of 30.88, 21.64, and 12.40 mg kg^-1 in leaf B content were observed at 30, 60 and 90 days, respectively, after application of the highest dose of B compared with the control (Figure 6a2). Similar to the other periods, at 120 days, B levels stabilized at 18.92, 19.54, 20.17, 20.80, 21.43, and 22.06 mg kg^-1 (Figure 6a2). In this third period, there was no correlation between the B applied to the soil and the B content in the leaves, likely due to the intense leaching of the applied B, which hindered its absorption and translocation.

Therefore, it was shown that B fertilization via stipe can be useful due to the rapid increase in leaf B content, maintenance of B nutritional status at high levels to support high coconut yields, and correction of B deficiency or hidden hunger. It is suggested that this fertilization alternative is more appropriate during rainier periods, when B fertilization via soil is strongly affected by leaching, especially in sandy soils.

During this period, rainfall was high (Figure 1), which may have led to B leaching into regions with lower absorbent root (rootlet) content and reduced transpiration, limiting the absorption of B applied to the soil (Abreu-Junior et al., 2025). Furthermore, considering that B absorption via soil is substantially reduced during periods of high rainfall (Das and Purkait, 2020; Samreen et al., 2021), the application of B via stipe during this period is important and promising as an alternative to increase B levels in the leaf and, consequently, its nutritional status. However, this was due to the low efficiency of applying B to the soil. Application via the stipe was more efficient at any time, even showing greater increases in leaf B levels during the dry period than during the wet periods.

Generally, these periods of higher rainfall correspond to lower temperatures, which result in limited transpiration and reduced mass flow, limiting B absorption by the coconut grove (Karthika et al., 2018). This results in increased fruit abortion and, consequently, a reduction in the number of fruits per plant due to B deficiency in the plant. Consequently, nutrition with B via the coconut palm stipe showed a rapid and efficient response, constituting a promising alternative for increasing this nutrient in the leaf, especially during the period of highest rainfall, even with lower B doses used in fertilization, compared with the soil method. In addition, this technique can also be useful as a complement to conventional fertilization in commercial production areas, enabling a reduction in the amount of B fertilizer applied to the soil.

Effect of B dose and application method, regardless of timing, on B content in leaves

Effects of soil application of B on leaf B content were small (Figure7), suggesting that this would not be the best way to apply B to increase leaf B content. Conversely, when B was applied via stipe, the effects on leaf B content were pronounced regardless of the application period (Figure 7), although this effect was greatest in the second period, in which leaf B increased by 2.3188 mg kg^-1 for each gram of B applied via stipe (Figure 7b). Stipe application resulted in a rapid increase in leaf B content because the nutrient is applied directly into the xylem.

Figure 7
Boron content in dwarf-green coconut palm leaves as a function of B doses applied via stipe and soil in the three evaluation periods: first period (a), second period (b), and third period (c). The data represent the averages for the 2021/2022 and 2022/2023 growing seasons. * Represents the significance by the F-test (p<0.05) of the effect of each dose of B applied via stipe compared with application via soil.

Given this rapid movement of B during the first days after stipe application, this method can constitute an efficient management practice when morphological deficiencies or perceptible “hidden hunger” for B are detected, since it is a rapid-acting alternative to minimize or even eliminate the deficiency.

The effect of B doses applied via stipe and via soil on leaf B content diverged from the 4 g plant^-1 dose onward, irrespective of the application period (Figure 7). From that dose, the difference widened and was markedly more pronounced in the third application period (Figure 7c), which coincided with the highest rainfall levels (Figure 1).

These results revealed that B application during the period of highest rainfall is substantially reduced, particularly during the third application period, when no difference was found between the control (without B) and soil-applied B at all applied doses (Figure 7c). In this context, stipe application constitutes an alternative to B fertilization aimed at maintaining nutritional status or correcting deficiencies (“hidden hunger”) of this nutrient, especially during this high-rainfall period. This “hidden hunger” is highly detrimental to coconut palms (Holanda et al., 2007; Ribeiro et al., 2016).

It is noteworthy that the control (without B application), despite exhibiting a low leaf B content (19 mg kg^-1; Figure 7), did not display any visual deficiency symptoms. However, other studies have shown that, even in the absence of these symptoms, plants experienced “hidden hunger” and exhibited effects on fruit setting and yield (Holanda et al., 2007; Ribeiro et al., 2016).

Moreover, climatic conditions can not only negate the short-term effect of soil fertilization on leaf B contents, as observed in the third application period, but also eliminate medium-term residual effects post-application and produce long-term consequences reflected in a reduced number of fruits per bunch. This medium- and long-term effect of reduced B availability to plants due to high rainfall was reported by Shorrocks (1997) for various cultivated species worldwide.

In coconut cultivation, the impact is even greater, with effects becoming evident 18-20 months after the start of each coconut production cycle, because differentiation of female flowers occurs 11-12 months before spathe opening and harvest occurs 7-8 months thereafter. The reduced number of flowers is primarily attributable to nutritional conditions, especially B nutrition (Kamalakshiamma, 2005; Holanda et al., 2007). In this context, because coconut palms exhibit continuous flowering, with inflorescences emerging every 20-30 days (Medeiros et al., 2022), maintaining adequate B levels more consistently promotes higher yields. This persistence of adequate B content was observed only with stipe fertilization, provided that fertilization is performed every 4 months, i.e., 3 times per year (Figures 4, 5, and 6).

Abd-Elhaliem et al. (2017) and Zokaee et al. (2023), when investigating the applications of B and Fe via stipe, respectively, found that this method was more effective at increasing foliar nutrient content and correcting deficiencies in date palm and peach, respectively, compared with soil fertilization. Broschat and Doccola (2010) conducted a study on the application of Mn via stipe in coconut palms and reported that this application method was the most effective at increasing foliar Mn content.

Adequate nutritional status should be a priority throughout the entire coconut production cycle, and special attention should be paid to the high-rainfall period, as in the Platô de Neópolis region, where rainfall exceeds 250 mm in a single month (Figure 1). Temporary deficiency is common and intensifies fruit abortion, as occurs in coconut palms during periods of high rainfall (Athulya, 2017). Thus, stipe fertilization is an alternative to promote significant increases in leaf B content, particularly during this period.

Coconut palm production as a function of B dose and application method

Dwarf-green coconut palm yield increased with increasing B doses, regardless of application method; however, when B was applied via stipe, yield was higher than when applied via soil (Figure 8).

Figure 8
Production of dwarf-green coconut palm as a function of B doses applied via stipe and soil. The data represent the averages for the 2021/2022 and 2022/2023 growing seasons. * Represents the significance by the F test (p<0.05) of the effect of each dose of B applied via the stipe compared with application via soil.

The growth rate of this yield also varied with the B application method. When the nutrient was applied via soil, there was a linear increase in yield, and when applied via stipe, the growth rate was curvilinear, with a quadratic effect, indicating that, for this application method, B demand was satisfied and yield reached a level as a function of B application.

During the trial, no toxicity symptoms were observed with B application via stipe. Therefore, the observed quadratic effect signified physiological saturation (Figure 8), with the plant reaching an internal critical level of B, ceasing to be a limiting factor. On the other hand, the B content in the leaf continued to increase (Figure 7), even with physiological B saturation. This may have caused nutritional imbalances and reduced productivity at the highest dose of B applied.

Conversely, when application was via soil, the B demand was not satisfied, indicating that more B could be supplied by applying higher doses or that excessive B losses by leaching occurred, with little uptake by the plants. Given the previously observed lower leaf B contents following soil application (Figure 7), it is more likely that B leaching occurred, particularly because the soils are sandier (Table 1) and that in some periods of the year they were subject to high rainfall rates (Figure 1).

The stipe-applied B dose that produced the highest dwarf-green coconut palm yield was approximately 8.0 g plant^-1 yr^-1, divided into three applications. This dose yielded approximately 327 fruits plant^-1 yr^-1. When application was via soil, a dose of 10 g plant^-1 yr^-1 produced approximately 296 fruits plant^-1 yr^-1, that is, even applying 25 % more B via soil than via stipe, yield was 9.5 % lower with soil application than with stipe application (Figure 8).

Dwarf-green coconut palm yield without B application was approximately 250 fruits plant^-1 yr^-1, consistent with the soil B contents (Table 1) and with the leaf B contents of the control plants (Figure 7). Sobral et al. (2009) reported that for leaf B contents of 20 mg kg^-1 and soil B contents around 0.6 mg dm^-3, a yield of 200–250 fruits plant^-1 yr^-1 is expected, as observed in this study.

Critical B level in the leaves

The critical levels of B in the leaves of the dwarf-green coconut palm varied both with the method of B application and with the time of year in which B was applied (Table 2). Critical B levels were higher when B was applied via stipe than when B was applied via soil, regardless of the time of year (Table 2). The critical level of a nutrient in leaves typically does not depend on the application method (stipe versus soil), but in this case, the stipe application method was able to increase the diagnostic coconut leaf by 1.67719, 2.3188, and 1.6239 mg kg^-1 of B for each g plant^-1 of B applied in the first, second, and third application periods, respectively (Figure 7). These increases were 3.2 times greater than when B was applied via soil. Therefore, there must have been sufficient internal concentration of B to provide adequate redistribution, achieving maximum fruit production, when B was applied via stipe. When B was applied via soil, there must not have been adequate redistribution because there was not enough B, which did not allow quadratic adjustment of the data. The critical level, in this case, was estimated by associating it with the highest dose of B applied. On the other hand, the critical leaf level is not a fixed value, being influenced by the crop productive potential and by the environmental and physiological conditions that modulate nutrient demand (Kurihara et al., 2005).

Table 2
Critical levels of B in the leaf of dwarf-green coconut palm after B application via stipe and soil during the B application periods in the 2021/2022 and 2022/2023 growing seasons

Application period	Critical levels of B in the leaf
	B via stipe	B via soil
	––––––––––––––– mg kg-1 –––––––––––––––
First period	32.40 Ab	24.93 Ba
Second period	38.22 Aa	26.19 Ba
Third period	30.40 Ab	18.63 Bb
Annual mean	33.67	23.25

• Means followed by the same uppercase letter in the rows and lowercase letters in the columns do not differ statistically from each other by Tukey test (p<0.05). The data represent the means of the periods of the 2021/2022 and 2022/2023 growing seasons.

The largest difference in critical leaf B level between stipe-applied and soil-applied B occurred in the third application period, that is, during the wettest period of the 2021/2022 and 2022/2023 growing seasons (Figure 1). The critical B level when B was applied via stipe in that period was approximately 63 % higher than when B was applied via soil (Table 2). Additionally, in the first and second periods these differences were smaller, with critical B levels being 30 and 46 % higher, respectively, when application occurred via stipe, compared with application via soil (Table 2).

Critical leaf B level for stipe application in the second period was 26 % higher than the critical level in the wettest period, i.e., the third period, and 18 % higher than in the first period (Table 2). When B was applied via soil, the critical leaf B level in the wettest period (third period) was approximately 30 % lower than in the driest period (second period) (Table 2). The third period was characterized by high rainfall rates (Figure 1), which reduced transpiration and the B absorption process. If the nutritional demand for B is high and there are inadequate B levels during the critical periods of pollen formation, it can result in sterility and poor fruit set (Shorrocks, 1997) and, consequently, reduced yield.

Variation in critical B levels during different periods of the year suggests that the best time to perform foliar diagnosis of B in irrigated dwarf-green coconut palms is from November to February, indicating that nutritional requirements are more associated with metabolic intensity and transpiration than with soil water availability. When temperature, radiation, and evaporative demand increase, metabolism, photosynthesis, and transpiration also increase; the plant becomes more active, and the nutritional requirement for B grows.

The average annual critical level of B in the leaf, when B was applied via stipe, was approximately 34 mg kg^-1 for a yield level of 327 fruits plant^-1 yr^-1, and approximately 23 mg kg^-1 for a yield level of 296 fruits plant^-1 yr^-1 when B was applied via soil (Table 2). These values exceed those reported by Sobral et al. (2009) and the recommendation for the Sergipe region (20 mg kg^-1). It is noteworthy that the critical levels reported by Sobral et al. (2009) were established 16 years ago for soil-applied B and for an expected yield of 200-250 fruits plant^-1 yr^-1. It is important to emphasize that the critical foliar levels established in this study were associated with the dose that resulted in the highest fruit production, highlighting the physiological and agronomic aspects, considering that at this dose, B ceased to be a limiting factor for growth and production, becoming present in sufficient quantity to support the productive potential.

Older studies than those of Sobral et al. (2009), such as Santos et al. (2004), recommended a critical level of 19.6 mg kg^-1 for a yield of 227 fruits plant^-1 yr^-1. These contrasting results indicate that the regional critical level is outdated and needs revision, considering current yield levels, because critical levels vary with yield (Sobral, 1998; Silva et al., 2009). In a survey of 112 coconut palm plots in the São Francisco Valley, a critical leaf B level of approximately 39 mg kg^-1 was reported for a high-yield population exceeding 300 fruits plant^-1 yr^-1 (Santos, 2020). Considering that leaf B contents are influenced by edaphoclimatic conditions, yield levels, and management (Sobral, 1998; Silva et al., 2009), it is always necessary to update local nutritional reference standards.

Increase of leaf B content via stipe application and xylem tissue morphology

There was an increase in B contents in leaves of dwarf-green coconut with increasing doses of B applied on the stipe, regardless of the growing seasons (Table 3), without the plants showing any symptoms of toxicity in their leaf structures. However, when the B was applied, from the dose of 8 g plant^-1 yr^-1 onward, the increment in leaf B content was significantly smaller between the 2021/2022 and 2022/2023 growing seasons, in other words, with the second B application, there was a significant reduction in the increment of leaf B. This reduction was 37 and 40 % at the doses of 8 and 10 g plant^-1 yr^-1, respectively (Table 3). It is important to note that, when the increases in leaf B content were evaluated in the 2022/2023 growing season, the entire B application for the 2021/2022 season had already been completed. Furthermore, it is also important to highlight that leaf B content was growing in both crop seasons (Figure 7); what decreased was the increase in leaf B content, that is, the difference in leaf B content between the control and the higher dose of B applied in the two crop seasons (Table 3).

Table 3
Increases in B content in dwarf-green coconut palm after application of B (MEA and boric acid) in relation to the control (without B application), comparing the growing seasons

B doses(1)	Increase in B content compared to the control
	First period/2021	First period/2022
g plant-1	––––––––––––––––––––––––– mg kg-1 –––––––––––––––––––––––––
2	8.88 a	6.98 a
4	15.11 a	11.47 a
6	18.82 a	14.90 a
8	25.39 a	16.00 b
10	37.73 a	22.77 b
Boric acid (5 g plant-1)	14.47 a	12.37 a

• ⁽¹⁾
  The doses of B and boric acid were split into three applications; Means followed by the same letter in the row do not differ statistically by the F test (p<0.05).

Given the absence of toxicity symptoms under increasing B application rates, and considering that stipe injection is widely used in palms for delivering phytosanitary products (Ferreira et al., 2023, 2024), the smaller increase in leaf B concentration between the two crop seasons was likely attributable to the B source used.

When an additional control consisting of a single dose of 5 g plant^-1 yr^-1 of boric acid was used in the two crop seasons, it was found that there was no reduction in the increase in leaf B content between the 2021/2022 and 2022/2023 crop seasons (Table 3).

These results indicated that, as B applications were performed using MEA at higher doses, the plant was no longer able to transport the fertilizer rapidly. At 30 days after B application from the MEA source in the 2022/2023 growing season at doses of 8 and 10 g plant^-1 yr^-1, the presence of fertilizer in the catheter was still observed, characterizing necrosis of the xylem tissues, reducing transpiration flow (Figure 9). This is a negative effect of fertilization by this technique, which can be explained by the progression of necrosis in the internal tissues of the stipe. Necrosis of internal tissues has been reported with the use of insecticides and fungicides applied via the stipe in coconut (Ferreira et al., 2024). Broschat and Doccola (2010) conducted a study of Mn application via stipe in coconut and reported tissue necrosis.

Figure 9
Images of the morphology of the xylem tissues (a, c, and e) and sap coloration (b, d, and f) of dwarf-green coconut palm after application of a dose of 10 g plant^-1 yr^-1 of B in the first application period (a) and (b) in the 2021/2022, as well as in the second application period (c) and (d) and at the end of the trial (e) and (f) in the 2022/2023.

When pH and electrical conductivity of the sap were measured 30 days after MEA-source B application in the 2022/2023 season as a function of applied B doses, both sap pH and electrical conductivity increased with increasing B doses (Figure 10). Boron in the MEA source is complexed by monoethanolamine, which has a high pH value (7.9), and the electrical conductivity of the fertilizer diluted in water exceeded 15 mS cm^-1. Therefore, the saline effect of MEA‑source B may have exerted osmotic pressure that reduced the availability of free water around the application region, causing necrosis. Conversely, sap pH in the control (boric acid) varied between 3.5 and 4.0, whereas MEA-source B with pH 7.9 excessively raised sap pH, causing necrosis and a high risk of microbial contamination of meristematic tissues.

Figure 10
pH (a) and electrical conductivity (b) of the sap collected 30 days after B application via the stipe in dwarf-green coconut palm. The data represent the averages for all B application periods for the 2021/2022 and 2022/2023 growing seasons.

By contrast, B application using boric acid did not cause tissue necrosis, because the chemical characteristics of this B source are similar to those of sap, particularly with respect to pH. It is noteworthy that the dose used for this source was only 5 g plant^-1 yr^-1, because higher doses require large dilutions due to the low solubility of boric acid, making stipe application unfeasible.

Additionally, despite the effect of pH and electrical conductivity of MEA on xylem tissues, it cannot be disregarded that B applied via stipe at higher doses may have caused toxic effects on vascular tissues, such as damage to cell membranes (Zhou et al., 2025), cell wall rupture (Zhaou et al., 2024), and alteration in water transport via xylem (Macho-Rivero et al., 2018).

These damages to the xylem tissues, regardless of whether they resulted from the pH or electrical conductivity of the MEA or even from physiological toxicity of B in the xylem vessels, were only related to productivity at the highest dose of B applied (10 g plant^-1 yr^-1), reducing fruit production (Figures 8 and 9). Therefore, applications of B via stipe at doses higher than 8 g plant^-1 yr^-1 can reduce the productivity of dwarf-green coconut plants due to damage caused to the xylem vessels.

Considering that necrosis is permanent, leading to inactivation of the treated region and therefore requiring a new orifice in another part of the plant when necrosis is detected, for this technique to be sustainable in the medium and long term, with the possibility of performing multiple fertilizer applications through a single orifice, further studies will be necessary, considering that future lines of research should be related to the availability of specific nutritional formulations, employing this or other commercial products for application via trunk, focusing on the reaction of the coconut palm vascular system, in such a way as to reduce tissue necrosis substantially.

CONCLUSIONS

Application of Boron via stipe resulted in a greater increase in B levels in the leaves than application via soil. The application of B via stipe at a dose of 8 g plant^-1 yr^-1 divided into three applications provided a yield of 327 fruits plant^-1 yr^-1, which is the most suitable for dwarf-green coconut palms in the Platô de Neópolis region. The critical level of B in the leaf was approximately 34 mg kg^-1 when B was applied via stipe and approximately 23 mg kg^-1 when B was applied via soil. Application of B via stipe using complexed sources of B and in high doses, such as 10 g plant^-1 yr^-1, caused necrosis of the internal tissues of the coconut tree, suggesting the search for specific nutritional solutions for coconut trees when the application is via stipe using complexed B.

How to cite:

Oliveira M, Freire FJ, Matias GS, Moura MF, Sabino EM, Sales DS, Saldanha ECM, Galindo ASS. Boron applied via stipe in dwarf-green coconut: leaf boron content, yield, and xylem tissue morphology. Rev Bras Cienc Solo. 2026;50:e0250209. https://doi.org/10.36783/18069657rbcs20250209

DATA AVAILABILITY

All data was generated or analyzed in this study.

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*

Corresponding author: e-mail: [e-mail]

Editor:

José Miguel Reichert https://orcid.org/0000-0001-9943-2898 and Adelson Paulo de Araújo https://orcid.org/0000-0002-4106-6175

Publication Dates

• Publication in this collection
  09 Nov 2026
• Date of issue
  2026

History

• Received
  05 Feb 2026
• Accepted
  11 May 2026