Abstract Soil-applied inorganic fertilizers remain the foundation of modern rice production, yet their efficiency is often constrained by nutrient losses through leaching, volatilization, and fixation, ultimately limiting plant uptake and yield potential. Seaweed-based foliar fertilizers have attracted increasing attention because they provide nutrients that can stimulate plant growth and nutrient assimilation. However, their effectiveness when integrated with conventional soil fertilization under field conditions remains insufficiently understood. Therefore, a field experiment was conducted at the Agricultural Experiment Center, Central Mindanao University, to evaluate the combined effects of seaweed-based foliar and soil-applied inorganic fertilization on nutrient uptake efficiency and rice productivity. The combined application of inorganic and foliar fertilization (IF+FF) produced 25–135% and 29–129% significantly higher tiller number at 50 days after transplanting and panicle number, respectively, than the other fertilization treatments, demonstrating the synergistic benefits of integrated nutrient application. While full inorganic fertilization (IF) increased grain yield by 9% compared with foliar fertilization alone (FF), however, grain yield and overall nutrient uptake did not differ significantly between the IF and IF+FF treatments, indicating that the full inorganic fertilization rate was sufficient to satisfy crop nutrient demand and that supplemental foliar fertilization provided no additional agronomic benefit under these conditions. Future studies encompassing broader nutrient profiling, multiple foliar fertilizer formulations, and diverse soil environments are needed to elucidate the physiological mechanisms governing crop responses and to identify conditions under which foliar fertilization can complement recommended inorganic fertilizer regimes.

Keywords: Foliar fertilization, Soil-applied fertilization, Nutrient uptake, Rice productivity, Yield optimization

Citation:  Cristobal, J.U., Canatoy, A.M.R., Achondo, I.C., and Canatoy, R.C. 2026. Integration of foliar and soil-applied fertilization for enhanced nutrient uptake and productivity in rice paddy systems. Natural and Life Sciences Communications. 25(4): e2026098.

Graphical Abstract:

INTRODUCTION

Rice constitutes a principal food source, sustaining nearly half of the global population through regular consumption. It contributes approximately 20% of the world’s total dietary energy intake, exceeding the contributions of wheat and maize, which account for 19% and 5%, respectively (Darko et al., 2025). In certain Asian nations, rice comprises over 70% of caloric consumption (GRiSP, 2013). Moreover, rice serves as an indispensable staple for economically disadvantaged and undernourished populations across Asia and Africa, where access to alternative nutrient-rich foods remains either financially prohibitive or logistically unfeasible (Nugroho et al., 2025). Given its critical role in ensuring global food security, rice is not only fundamental to sustenance but is also intrinsically linked to economic stability, employment generation, social cohesion, and regional security (Yadav and Kumar, 2018).

Rice production systems worldwide face unprecedented challenges in sustaining yields while confronting the environmental consequences of conventional fertilization practices. Recent studies across major rice-growing regions reveal a concerning pattern; soil-applied fertilizers in flooded paddy conditions particularly under intermittent flooding scheme demonstrated a disappointingly low nutrient use efficiency of 22.5% (Cowan et al., 2021) compared to continuous flooding, leading to substantial losses through leaching, volatilization, and denitrification (Zhang et al., 2023). This inefficiency not only represents significant economic waste but also contributes to greenhouse gas emissions, nutrient leaching, soil degradation, and water pollution, highlighting the urgent need for alternative fertilization strategies (Menegat et al., 2022; Govindasamy et al., 2023; Liu et al., 2024).

Foliar fertilization emerges as a transformative approach, with studies demonstrating leaf absorption rates of up to 95% under optimal conditions (Pettinelli, 2023). By delivering essential nutrients directly to the leaf surface, foliar application bypasses soil-related losses and could potentially reduce total fertilizer requirements while maintaining or improving grain yields (Fageria et al., 2009; Niu et al., 2021). Among foliar fertilizers, seaweed-based formulations have gained increasing attention because they not only supply essential nutrients but also contain naturally occurring bioactive compounds, including phytohormones, polysaccharides, amino acids, and antioxidants, which can stimulate root development, photosynthesis, nutrient assimilation, and plant resilience under environmental stress (Thamarai et al., 2025). These multifunctional properties make seaweed-based foliar fertilizers a promising complement to conventional soil fertilization for improving crop nutrient-use efficiency and productivity. The integration of foliar fertilization into rice production systems therefore represents a critical research frontier, particularly given its potential to enhance nutrient uptake efficiency in waterlogged conditions where root absorption is hindered (Kundu et al., 2020; Singh et al., 2025). However, significant knowledge gaps persist regarding the interaction effects between seaweed-based foliar and soil-applied nutrients on nutrient uptake, soil fertility, and rice productivity under field conditions.

This research addresses these fundamental questions through a comprehensive investigation of the physiological responses and yield components of rice under various combinations of foliar and soil-based nutrient management strategies. By bridging critical knowledge gaps in foliar nutrient dynamics and plant-soil interactions, this study aims to determine combined effects of foliar and soil-applied fertilization on nutrient uptake efficiency and crop productivity in rice paddy agroecosystem systems while assessing its impact on soil fertility parameters and nutrient availability in the rice paddy ecosystem.

MATERIALS AND METHODS

Location and description of experimental area, soil characteristics, and treatments

To evaluate the influence of foliar fertilization on rice growth and yield in comparison to conventional soil-applied fertilization, while simultaneously assessing its impact on soil fertility and nutrient availability within the rice paddy ecosystem, a representative mono-rice paddy field was selected at the Agricultural Experiment Center, Central Mindanao University, Philippines. The field has been exclusively cultivated for rice for over a century. The parent material consists of alluvium, classified under the Maapag series of the Inceptisol soil order (Mariano et al., 1955; PCARRD, 2006; Calalang and Colinet, 2014).

Representative composite soil samples were collected from the 0–20 cm soil layer before treatment application. In each experimental plot, several randomly distributed soil cores were obtained using a soil auger and thoroughly mixed to minimize spatial variability. The composite samples were air-dried under ambient laboratory conditions, gently ground to break up aggregates, and passed through a 2-mm sieve before physicochemical characterization. The processed samples were subsequently analyzed for selected soil physical and chemical properties following standard analytical procedures. The soil was characterized as silty clay, comprising 37% silt, 17% sand, and 46% clay. Analytical results indicated a very strongly acidic soil reaction (pH 4.89), marginal soil organic matter (SOM) content (4.42%), low extractable phosphorus (P) (3.10 mg kg⁻¹), and low exchangeable potassium (K) (0.15 cmolc kg⁻¹). Based on these characteristics, the full recommended inorganic fertilizer application rate was 80-60-100 kg ha⁻¹ of N, P₂O₅, and K₂O, respectively.

The study consisted employed a of randomized complete block design (RCBD) with five treatments, each replicated three times: (i) control, (ii) full recommended rate of inorganic fertilizer (RRIF), (iii) foliar fertilizer alone (FF), (iv) half the recommended rate of inorganic fertilizer combined with foliar fertilizer (½RRIF+FF), and (v) full recommended rate of inorganic fertilizer combined with foliar fertilizer (RRIF+FF). The foliar fertilizer used in this study was a commercially available organic formulation derived from seaweed extract wherein its nutrient concentrations are summarized in Table 1.

Table 1. Nutrient composition of the seaweed-based foliar fertilizer used in the study.

Experimental plot and design and treatment imposition

Experimental plots (8 m × 8 m) were arranged following a randomized complete block design (RCBD). To prevent lateral water movement and treatment cross-contamination, dikes were constructed around each plot. Additionally, each plot was equipped with a designated irrigation inlet and outlet to ensure controlled water management. On the day of transplanting, inorganic fertilizers were manually incorporated into the paddy soil at following the recommended application rate. Of the total fertilizer recommendation ratedose, 50% of nitrogen (N), 100% of P, and 70% of K were applied as basal fertilization. The remaining fertilizer was top-dressed in two subsequent applications: 20% of N on the 15^th day after transplanting (DAT) and the remaining 30% of N and K on the 45^th DAT.

Foliar fertilization treatment and application protocol

The commercial seaweed-based foliar fertilizer was applied at the manufacturer's recommended rate of 1.6 L ha⁻¹ (commercial formulation). The product was first diluted with water according to the manufacturer's recommended dilution ratio and then sprayed uniformly using a calibrated 16-L knapsack sprayer. Spraying was performed at a field spray volume equivalent to 160 L ha⁻¹ (10 knapsack loads ha⁻¹), ensuring that each experimental plot (8 × 8 m) received the proportional amount of the diluted spray solution corresponding to the recommended application rate. Foliar fertilizer was applied once weekly using a manual hand-pressure sprayer equipped with a fine-mist nozzle to ensure uniform coverage of the leaf surface while minimizing runoff. The first application was carried out after transplanting and continued until the rice plants reached the grain-filling stage. As this represents the final phase of active nutrient assimilation and remobilization toward the developing grains (Liu et al., 2025a; Hu et al., 2026). This application schedule ensured a continuous supply of nutrients throughout the crop growth cycle. Foliar spraying was conducted during the early morning (06:00–08:00) or late afternoon (16:00–18:00) to minimize rapid evaporation and nutrient photodegradation (Balachandra et al., 2025; Sikka et al., 2025). To maximize nutrient absorption, applications were made under calm weather conditions, avoiding periods of high wind velocity (>5 m s⁻¹) and forecasted rainfall within 24 h after application.

Rice crop production and data collection

 Twenty-one-day-old NSIC Rc 226 (Japonica) rice seedlings were used in this cropping season. NSIC Rc 226 is an early-maturing inbred rice variety developed by the Philippine Rice Research Institute (DA-PhilRice). It is adapted to irrigated lowland ecosystems and has an average grain yield of approximately 6 Mg ha⁻¹, with a yield potential of 9–12 Mg ha⁻¹. Rice seedlings were raised in a wet-bed nursery following standard agronomic practices. Healthy and uniform seeds were pre-soaked in clean water for 24 h and incubated for an additional 24 h to promote uniform germination before sowing. The pre-germinated seeds were evenly broadcast onto puddled nursery beds and maintained under adequate moisture throughout the nursery period. Seedlings were grown for 21 days, and only healthy, uniform seedlings were selected for transplanting into experimental plots.

Manual transplanting was performed using one to three seedlings per hill at a uniform spacing of 20 cm × 20 cm across all treatment plots. During the flooding period, irrigation water was supplied from the main irrigation canal and evenly distributed to each plot through designated inlets. The floodwater depth was maintained at 5–7 cm above the soil surface throughout the cropping season and was drained four weeks before harvest to facilitate grain maturation. At the tillering stage, 20 representative rice plants were randomly selected and tagged in each plot for growth assessments. These tagged plants were subsequently harvested for analysis. Plant samples were air-dried for one week, after which the grains were manually separated from the panicles and counted. The harvest index was calculated as the ratio of grain yield to total aboveground biomass. Additionally, soil samples were collected at harvest, air-dried, and passed through a 2-mm sieve for post-harvest soil property analyses.

Soil and plant tissue analyses

Soil organic matter content was determined using the Walkley–Black method as described by PCARRD (1991), while soil pH was measured following the method of Biddle (1997). Extractable P was quantified using the Bray P2 method as described by Sherrell (1970), and exchangeable K was extracted with 1 N ammonium acetate and determined using a flame photometer. Total N concentration in rice tissue samples was determined using the micro-Kjeldahl method as described by Ogg (1960). Total P concentration was determined using the vanadate–molybdate colorimetric method, with the vanadate–molybdate reagent serving as the colorimetric indicator for orthophosphate. Sample absorbance was subsequently measured using a UV–visible spectrophotometer to quantify total P concentration. Total K concentration in plant tissues was determined using the dry ashing method, followed by measurement with a flame photometer after calibration with K standard solutions. Rice plant nutrient uptake was calculated using the equation described by Sharma et al. (2012):

where nutrient uptake (kg ha⁻¹) is the total amount of a specific nutrient accumulated in the aboveground rice biomass per unit area; nutrient concentration (%) is the concentration of the nutrient in the oven-dried plant tissue, expressed as a percentage of dry weight; dry matter yield (kg ha⁻¹) is the oven-dry biomass of the plant component (e.g., grain or straw) used in the calculation. Total plant nutrient uptake was obtained by summing the nutrient uptake of the individual plant components.

Statistical analysis

Statistical analyses were conducted using Statistical Tool for Agricultural Research (STAR) version 2.0.1. One-way analysis of variance (ANOVA) was performed to evaluate treatment effects within the RCBD. Rice growth and yield parameters, as well as soil properties, were subjected to ANOVA to determine significant differences among treatments. When significant effects were detected (P < 0.05), mean comparisons were conducted using Tukey’s Honestly Significant Difference (HSD) test at a 5% significance level.

RESULTS

Growth, grain yield components and productivity of rice

To assess foliar fertilization effects on rice growth and yield, key agronomic and yield components were assessed. Results demonstrated a significant influence of foliar fertilization on these parameters (Table 2). Plant height at 30 and 50 DAT exhibited variable responses to foliar and soil-applied fertilizers. Notably, the combined application of inorganic fertilizer and foliar fertilization (IF+FF) resulted in a 24% and 31% increase in plant height compared to the control at 30 and 50 DAT, respectively. Moreover at 30 DAT, IF+FF was approximately 12% and 14% taller (P < 0.05) than IF and FF treatments, respectively.

Tiller production was similarly enhanced by IF+FF, with increase of 10.2% and 14.4% at 30 and 50 DAT compared to the control, respectively (Table 2). Moreover, IF application resulted in an approximately 29% higher tiller number relative to FF at 50 DAT. The number of panicles per plant was significantly higher in IF+FF than in the control of approximately 129%, whereas IF and FF treatments were significantly lower by 24% and 38%, respectively, relative to IF+FF. Hence, a comparable difference in panicle number was observed between IF and FF (P < 0.05). The number of grains per panicle, a key determinant of rice yield, was significantly higher in the IF+FF treatment than in the control, representing an increase of approximately 26%. However, no significant differences were observed among the IF, ½IF+FF and IF+FF treatments (P > 0.05). Likewise, the percentage of ripened grains was comparable between the IF+FF and IF treatments, with the IF treatment exhibiting a marginally lower value of approximately 4% (Table 2). In contrast, the FF treatment showed a 2% increase relative to the control; however, this difference was not statistically significant (P > 0.05).

The 1,000-grain weight in the control treatment was 25% lower than that in the IF+FF treatment. However, the IF+FF treatment was statistically comparable to all other fertilizer treatments (P > 0.05). Root biomass was lowest in the control (0.8 Mg ha⁻¹), representing reductions of approximately 27% and 25% relative to the IF and FF treatments, respectively. Finally, the harvest index, defined as the ratio of grain yield to total biomass (Table 2), did not differ significantly among treatments (P > 0.05).

Regardless of the fertilizer treatment, grain yield was significantly higher than that of the control (Figure 1). Specifically, the FF treatment increased grain yield by 24% relative to the control. Under the IF+FF treatment, grain yield increased by approximately 18% compared with the FF treatment. However, no significant difference was observed between the IF+FF and IF treatments (P > 0.05). Although grain yield under the FF treatment was 8% lower than under the IF treatment, the difference was not statistically significant.

Straw productivity was not significantly influenced under foliar fertilization (FF) treatment (Figure 1). Although FF treatment exceeded control by approximately 34%, the difference was not statistically significant (P > 0.05). The inclusion of full inorganic fertilizer in combination with foliar fertilization (IF+FF) resulted in a 6% increase in straw biomass over IF, likely attributable to the additional inorganic fertilizer application, however this increase was comparable (P > 0.05).

Aboveground biomass exhibited a strong response to foliar fertilization, with significant variations among treatments. Control treatment resulted in the lowest biomass accumulation, approximately 22% lower than that of FF. Although FF produced 10% less biomass than IF, the difference was not statistically significant (P > 0.05). Interestingly, the combined application of soil and foliar fertilization (IF+FF) led to the highest aboveground biomass, reaching 11.9 Mg ha⁻¹, representing an 8% to 55% increase across treatments. However, this increase was not statistically different with IF (P > 0.05).

Table 2. Rice yield components under foliar and soil-applied fertilization.

Note:  †Means with different letters indicate significant differences, as determined by HSD method with P < 0.05.

Figure 1.  Grain and straw biomass and nutrient uptake of rice under foliar and soil-applied fertilization. Vertical bars indicate standard deviations (n= 3).

Nutrient concentration and uptake of rice in grain and straw

To evaluate the efficiency of nutrient acquisition under different fertilization strategies, grain and straw nutrient concentrations were determined, and nutrient uptake was subsequently calculated. Grain N and P concentrations were significantly higher in the IF+FF treatment than in the control; however, they did not differ significantly from those in the IF treatment (Table 3). In contrast, grain K concentration was significantly highest in the IF+FF treatment among all fertilizer treatments (P < 0.05).

Table 3. Nutrient concentration in grain and straw under foliar and soil-applied fertilization.

Note: †Means with different letters indicate significant differences, as determined by HSD method with P < 0.05.

The FF treatment increased grain N, P, and K uptake by approximately 47%, 43%, and 40%, respectively, relative to the control. However, only the increases in N and K uptake were statistically significant, whereas P uptake did not differ significantly from the control (P > 0.05). Similarly, grain N and P uptake in the IF+FF treatment exceeded those in the IF treatment by approximately 15%; however, these differences were not statistically significant. Nevertheless, the combined application of inorganic fertilizer and foliar fertilizer (IF+FF) resulted in significantly greater grain N, P, and K uptake than the FF treatment alone, with increases of approximately 32%, 55%, and 61%, respectively (P < 0.05), indicating that the additional inorganic fertilizer substantially enhanced nutrient accumulation in grain.

Straw N, P, and K concentrations followed a similar trend to those observed in the grain. The IF+FF treatment exhibited significantly higher straw N, P, and K concentrations than the control, with increases of approximately 33%, 50%, and 17%, respectively. Although the IF+FF treatment recorded the highest straw P and K concentrations among all treatments, these values did not differ significantly from those of the IF treatment (P > 0.05). Likewise, straw N and K uptake in the ½IF+FF treatment was statistically comparable to that in the IF+FF treatment.

Relative to the control, the FF treatment increased straw N, P, and K uptake by approximately 45%, 57%, and 35%, respectively. However, only the increase in P uptake was statistically significant, while in N and K uptake were not (P > 0.05). Although the FF treatment exhibited 23%, 22%, and 21% lower N, P, and K uptake than the IF treatment, respectively, these differences were also not statistically significant (P > 0.05). In contrast, the IF+FF treatment resulted in significantly greater straw N, P, and K uptake than the FF treatment, with increases of approximately 49%, 53%, and 40%, respectively (P < 0.05). However, straw N, P, and K uptake in the IF+FF treatment did not differ significantly from that in the IF treatment, indicating that the addition of foliar fertilizer to a full inorganic fertilizer regime did not further enhance nutrient accumulation in straw.

Total aboveground nutrient uptake was lowest in the control treatment. Compared to control, FF enhanced N, P, and K uptake by approximately 46%, 48%, and 36%, respectively. Though no significant difference was observed in terms of K uptake (P > 0.05). IF treatment resulted in a significant increase of 19% and 32% in N and P uptake relative to FF (P < 0.05), while K uptake was 28% higher, but the difference was not statistically significant. The highest total nutrient uptake was observed in IF+FF, reaching 138 kg N ha⁻¹, 31.8 kg P ha⁻¹, and 113.5 kg K ha⁻¹. However, nutrient uptake between IF and IF+FF treatments remained statistically comparable (P > 0.05). Signifying that supplementing the recommended inorganic fertilizer regime with foliar fertilizer did not further enhance nutrient accumulation in the aboveground biomass.

Soil properties under foliar fertilization

To evaluate the foliar fertilization effects on soil fertility and nutrient availability in rice paddy, key soil properties were assessed at harvest (Figure 2). Soil pH and organic matter content exhibited no significant response to foliar fertilization (P > 0.05). However, extractable P was markedly influenced by foliar application. FF treatment increased extractable P by 45% compared to the control. While IF+FF recorded a 3% higher extractable P concentration than IF, the difference remained statistically comparable (P > 0.05). Similarly, ½IF+FF exhibited a 9% lower extractable P than IF, yet no significant difference was observed. Across treatments, IF+FF consistently yielded the highest extractable P, with increase ranging from 3% to 128%, however, differences remained non-significant between IF and ½IF+FF (Figure 2).

Figure 2.  Soil properties of rice paddy under foliar and soil-applied fertilization. Vertical bars indicate standard deviations (n= 3).

Exchangeable K was significantly influenced by foliar fertilization (P < 0.05). FF treatment resulted in a 137% increase in exchangeable K compared to the control. IF and ½IF+FF showed 11% and 7% higher exchangeable K concentrations than FF, respectively, though the differences were not statistically significant (P > 0.05). IF+FF exhibited the highest exchangeable K levels, reaching 0.54 cmolc kg⁻¹, representing an 8% to 184% increase across treatments. However, no significant difference was detected between IF and ½IF+FF. While FF was approximately 6% lower than ½IF+FF, the difference remained statistically comparable (P > 0.05).

DISCUSSION

Foliar fertilization is widely employed as a supplementary or alternative strategy to soil fertilization, primarily due to its high nutrient uptake efficiency and immediate physiological effects on plant growth. Unlike conventional solid fertilizers, which rely on root-mediated absorption and soil nutrient dynamics, foliar-applied nutrients bypass soil interactions and are absorbed directly through the leaf surface. This mechanism enhances nutrient availability, ensuring rapid assimilation and utilization for plant development (Rehman et al., 2021; Ishfaq et al., 2023).

In the present study, the FF treatment significantly influenced plant height and tiller production (P < 0.05), with increases of 9-17% and 47-100%, respectively, compared with the control (Table 2). These improvements can be attributed to the direct uptake of nutrients through the cuticle, stomata, and specialized epidermal structures. The leaf cuticle, a hydrophobic barrier, regulates nutrient permeability, with aqueous channels and microfractures facilitating the diffusion of water-soluble nutrients, particularly in younger leaves where cuticular resistance is lower (Machhar et al., 2021). Additionally, panicle number and root biomass increased significantly under the FF treatment by approximately 66% and 25%, respectively, relative to the control. These findings agree with those of Shaygany et al. (2012), who reported that foliar nutrient application at various growth stages significantly improved panicle density across multiple rice-growing seasons. Similarly, reports of Balachandra et al. (2025) and Arif et al. (2006) demonstrated that foliar fertilization positively affected key agronomic traits, including panicle density, straw yield, and grain yield.

Despite these improvements in vegetative and reproductive traits, no significant differences were observed between the FF and control treatments in grains per panicle, ripened grains, 1,000-grain weight, or harvest index (P > 0.05). Suggesting that although foliar-applied nutrients enhance metabolic activity and stress tolerance, they may not substantially alter grain allocation in the absence of nutrient deficiencies (Ibn et al., 2024). Given the efficient nutrient remobilization mechanisms in rice, particularly for N, grain filling may not be limited in either treatment when internal nutrient reserves are sufficient (Mahmoodi et al., 2020).

Interestingly, no significant differences were detected between the IF and ½IF+FF treatments across key yield components, including panicle number, grains per panicle, ripened grains, 1,000-grain weight, root biomass, and harvest index. These findings suggest that partial substitution of soil-applied fertilizer with foliar fertilization may sustain comparable yield performance, potentially improving fertilizer-use efficiency (Li et al., 2022; Chawla and Sharma, 2026).

Although the FF treatment increased grain yield by 11% compared with the control, the difference was not statistically significant (P > 0.05). This observation contrasts with that of Kundu et al. (2020), who reported a 25% increase in rice grain yield following foliar application of organic potassic salts. Similarly, Raj et al. (2024) observed a 12% yield enhancement following the application of moringa extract in India. These discrepancies could be attributed to differences in soil fertility status, rice genotype, and environmental conditions that influence nutrient uptake and grain filling. Rice plants exhibit efficient nutrient remobilization mechanisms, particularly for N, P, and K, which are translocated from vegetative tissues to reproductive organs during grain development (Padhan et al., 2023). It is likely that plants in both the control and FF treatments possessed sufficient internal nutrient reserves to maintain comparable grain yield components, including grains per panicle, ripened grains, and 1,000-grain weight. Additionally, foliar fertilizers are generally applied in relatively small quantities and may not fully satisfy crop macronutrient requirements when soil nutrient availability is already adequate (Ishfaq et al., 2022).

Grain yield did not differ significantly between the IF and IF+FF treatments. This finding suggests that the inorganic fertilizer recommended rate was sufficient to satisfy rice’s nutritional demand for achieving near-maximum grain production, thereby limiting the potential for additional yield gains from foliar nutrient application (Al-Yasari et al., 2024). Once nutrient supply approaches the optimum level, crop productivity is increasingly constrained by other factors, including sink capacity, assimilate partitioning, genetic yield potential, and prevailing environmental conditions rather than by further improvements in nutrient availability. Consequently, additional nutrient inputs may enhance plant nutritional status without necessarily translating into increased grain production (Paramesh et al., 2023).

The absence of a yield response despite foliar fertilizer supplementation also reflects the complex relationship between nutrient acquisition and grain formation (van Der Bom et al., 2025). Grain yield in rice is primarily determined by the balance between source activity and sink strength. Although foliar-applied nutrients may enhance leaf nutrient status, chlorophyll content, and photosynthetic efficiency, these physiological improvements contribute to greater grain yield only when reproductive sink capacity has not already been maximized. In the present study, the comparable grain yields between IF and IF+FF indicate that sink limitation, rather than nutrient availability, likely became the dominant factor regulating final yield. Similar observations have been reported in well-fertilized rice systems, where additional nutrient supplementation improves physiological traits or nutrient accumulation but produces minimal yield responses because grain filling and sink size have already approached their physiological limits (Zhao et al., 2022; Liu et al., 2025b).

Conversely, rice straw yield was 47% higher under the FF treatment than under control (Figure 1), however, this increase was not statistically significant (P > 0.05). This response may be related to N uptake by the rice straw (Akter et al., 2024). The results revealed comparable straw N uptake between the FF and control treatments. Moreover, FF treatment may improve straw yield only to a limited extent. In contrast, combining soil-applied and foliar fertilizers appears to enhance crop productivity. For example, the ½IF+FF and IF+FF treatments produced significantly higher straw yields than the control. This could be a complementary effect of soil- and foliar-applied fertilizers, which provide both sustained root nutrient supply and rapid foliar nutrient absorption (Ssemugenze et al., 2025). Mobile macronutrients such as N, P, and K are essential for vegetative growth and biomass accumulation (Kumar et al., 2021; Wang et al., 2021). The greater straw biomass observed under the integrated fertilization treatments was closely associated with enhanced plant N uptake (Figure 1; Table 3). In particular, the ½IF+FF and IF+FF treatments exhibited significantly higher N uptake than the control, suggesting improved plant N acquisition. Consequently, increased N uptake enhances leaf chlorophyll content, photosynthetic capacity, and assimilate production, thereby promoting tiller development and vegetative growth (Olanlokun et al., 2026). The combined application of soil-applied inorganic fertilizer and foliar fertilizer likely improved the overall nutritional status of the crop, sustaining greater leaf area development and biomass accumulation, which ultimately contributed to the higher straw yield. These findings are consistent with those of Görlach et al. (2021), who reported that improved plant N nutrition enhances vegetative growth and biomass production by increasing photosynthetic efficiency.

The FF treatment significantly increased aboveground biomass, producing a 29% greater biomass yield than the control (P < 0.05). This enhanced biomass accumulation can be attributed to the rapid absorption of nutrients through the leaf surface, thereby bypassing soil-mediated constraints such as nutrient fixation, leaching losses, and limited root uptake efficiency (Islam et al., 2023). Unlike soil-applied fertilizers, which are subject to complex biogeochemical interactions, foliar fertilizers deliver nutrients in highly bioavailable forms, allowing immediate metabolic utilization (Ishfaq et al., 2022; Bouranis and Chorianopoulou, 2023). This rapid uptake mechanism enhances photosynthetic activity by increasing N availability, promoting chlorophyll synthesis, optimizing carbohydrate production, and ultimately facilitating greater biomass accumulation.

Interestingly, the IF treatment produced 13% and 11% greater aboveground biomass than the FF and ½IF+FF treatments, respectively, although these differences were not statistically significant (P > 0.05). The comparable biomass production among the IF, FF, and ½IF+FF treatments suggests that these nutrient management strategies supplied sufficient nutrients to sustain vegetative growth. Aboveground biomass is primarily determined by cumulative carbon assimilation, which depends on adequate nutrient availability during the vegetative stage (Oldfield and Peterson, 2021). Under these conditions, foliar fertilization likely acted as a supplementary nutrient source that partially compensated for the reduced soil fertilizer rate, thereby maintaining biomass production comparable to that of the IF treatment (Ssemugenze et al., 2025). In contrast, the IF+FF treatment significantly increased aboveground biomass relative to the FF and ½IF+FF treatments (P < 0.05), indicating that maximizing nutrient availability through both soil and foliar pathways enhanced nutrient uptake and photosynthetic capacity, resulting in greater biomass accumulation (Song et al., 2025). However, the absence of a significant difference between the IF and IF+FF treatments suggests that soil-applied nutrients alone were sufficient to meet the crop's demand for vegetative growth. Consequently, the additional nutrients supplied through foliar application provided only a marginal benefit that was insufficient to produce a statistically detectable increase, reflecting the diminishing response of biomass accumulation once nutrient requirements for maximum vegetative development had largely been satisfied. While the present study focused on N, P, and K because these macronutrients are the primary determinants of rice productivity and the principal nutrients supplied through conventional fertilization, the commercial foliar fertilizer used also contained other macro- and micronutrients that were not evaluated. Consequently, the potential contribution of these additional nutrients to crop performance could not be determined. Future studies incorporating a broader range of plant nutrient analyses may provide a more comprehensive understanding of the physiological responses associated with foliar fertilization.

Moreover, rice N, P, and K uptake is governed by distinct physiological and biochemical mechanisms that optimize nutrient absorption and translocation (Cao et al., 2025). A substantial proportion of these nutrients is remobilized from vegetative tissues to developing grains during grain filling. In this study, approximately 71–75% of total N, 56–62% of P, and 14–18% of K were allocated to the grains, while the remaining nutrients were retained in the rice straw (Figure 1 and Table 3). The differential partitioning of these macronutrients highlights the dynamic role of nutrient remobilization in rice productivity (Sánchez-Reinoso, 2019).

Combined soil and foliar fertilization (½IF+FF and IF+FF) significantly enhanced N, P, and K uptake compared with the control, primarily because of the direct nutrient delivery mechanism of foliar fertilization (Fernández and Eichert, 2009; Hong et al., 2021; Song et al., 2025). Unlike soil-applied fertilizers, which are subject to nutrient losses through fixation, leaching, and restricted root activity under submerged conditions, foliar-applied nutrients bypass these constraints (Barlog et al., 2022; Kumawat et al., 2022; Bhardwaj et al., 2025). Because foliar fertilizers are commonly supplied in mineral or readily available forms, they are rapidly absorbed through the leaf cuticle and stomata, facilitating immediate entry into plant metabolic pathways (Hou et al., 2021). This direct uptake not only minimizes nutrient losses, particularly in flooded rice systems prone to N volatilization (Chu et al., 2023), P fixation (Nishigaki et al., 2021), and K leaching (Vijaya et al., 2021) but also improves nutrient-use efficiency. The enhanced nutrient availability resulting from foliar fertilization increases photosynthetic capacity, leading to greater carbohydrate production, increased tillering, and more vigorous biomass accumulation, all of which collectively contribute to greater nutrient uptake and improved plant performance (Harish et al., 2022; Bărdaş et al., 2023).

Comparative analysis of aboveground nutrient uptake revealed that the IF treatment resulted in 23% higher N uptake than the ½IF+FF treatment (P < 0.05), whereas P and K uptake remained comparable between the two treatments. This difference is likely attributable to the greater efficiency of root-mediated N absorption. Soil-applied N fertilizers dissolve in the soil solution, making them readily available for uptake through mass flow and diffusion, thereby ensuring a sustained N supply that supports chlorophyll synthesis, photosynthetic activity, and biomass accumulation (Barłóg et al., 2022; Yahaya et al., 2023; Claassen and Steingrobe, 2024).

Phosphorus uptake, which primarily occurs through diffusion (Lambers, 2022), is largely influenced by soil properties rather than fertilizer application rate alone, which may explain the comparable aboveground P uptake between the IF and ½IF+FF treatments (Zhang et al., 2024). In contrast, K is absorbed predominantly through mass flow because of its high solubility and mobility in the soil (Volf et al., 2022). The efficient translocation of foliar-applied K likely compensated for the reduced soil-applied K in the ½IF+FF treatment, thereby maintaining overall K uptake at levels comparable to those of the IF treatment. These findings highlight the importance of integrating soil and foliar fertilization to optimize nutrient uptake efficiency and improve rice productivity under varying soil and environmental conditions.

The negligible differences in soil pH and organic matter content between the control and FF treatments highlight the limited interaction of foliar-applied nutrients with the soil. Unlike soil-applied fertilizers, which undergo complex transformations and influence soil chemistry, foliar-applied nutrients are predominantly absorbed by plant tissues, with only trace amounts reaching the soil through leaf abscission or root exudation. Consequently, their influence on soil chemical properties remains minimal. This stability is further reinforced by the inherent buffering capacity of flooded rice paddy soils, which is driven by redox-mediated reactions and the presence of carbonates, clay minerals, and organic matter that collectively mitigate pH fluctuations (Lu et al., 2022; Wisawapipat et al., 2024). Likewise, the similar organic matter content across treatments can be attributed to the absence of direct organic inputs from foliar fertilization and the comparable contribution of plant residues at the end of the growing season. Although foliar fertilization enhances plant physiological processes, its influence on soil chemical properties appears limited. In contrast, long-term soil fertilization studies, such as that of Wang et al. (2019), reported a consistent annual decline of 0.07 pH units over 20 years in a Chinese rice paddy under continuous NPK fertilizer application, highlighting the cumulative effects of soil-based nutrient inputs.

Despite 10% and 4% higher extractable P and exchangeable K in the IF treatment than in the ½IF+FF treatment, these differences were not statistically significant (P > 0.05). This finding is consistent with the well-established mechanisms governing nutrient solubility in flooded rice ecosystems. Phosphorus availability is largely controlled by the redox-induced dissolution of Fe- and Al-bound phosphates (Martinengo et al., 2023), ensuring sustained P availability across treatments even when soil-applied P is reduced in the ½IF+FF treatment. At the same time, the efficiency of foliar-applied P in meeting plant demand may compensate for the reduced soil P application. Similarly, K, a highly mobile nutrient transported primarily through mass flow and diffusion, maintained comparable exchangeable K levels across treatments, with foliar-applied K being rapidly absorbed through the leaf cuticle and efficiently translocated within the plant.

However, the pronounced increase in extractable P and exchangeable K observed in the FF-treated plots relative to the control (Figure 2) highlights the complex interactions among plant nutrient demand, root uptake efficiency, and nutrient cycling. The enhanced metabolic activity stimulated by foliar fertilization likely increased root nutrient acquisition, thereby depleting soil P and K reserves. Under flooded conditions, P undergoes dynamic redox transformations in which anaerobic conditions enhance the solubility of Fe- and Al-bound P. Increased root activity in foliar-fertilized plants may have accelerated P uptake, resulting in lower extractable P concentrations. Similarly, exchangeable K, which exists both in the soil solution and adsorbed onto clay particles, is rapidly assimilated by actively growing rice plants. Because foliar fertilization promotes plant vigor and biomass accumulation, the resulting increase in K demand may have contributed to the depletion of exchangeable K in the soil (Singh et al., 2021).

These findings highlight the role of foliar fertilization in influencing nutrient cycling within rice paddy ecosystems. Although its direct effects on soil properties remain limited, its ability to enhance plant physiological processes alters nutrient dynamics and reinforces the intricate feedback mechanisms between plant nutrient acquisition and soil nutrient availability. Understanding these interactions is essential for developing fertilization strategies that simultaneously maximize crop productivity and sustain long-term soil fertility in intensively cultivated rice systems. Moreover, this study’s findings should be interpreted within the scope of the experimental conditions. The experiment was conducted at a single location during one growing season using a single commercial foliar fertilizer formulation. Consequently, the observed responses may vary under different soil types, climatic conditions, fertilizer compositions, or crop management practices. Moreover, only N, P, and K dynamics were evaluated, despite the commercial foliar fertilizer containing additional nutrients that may influence plant growth and nutrient use efficiency. Multi-location experiments evaluating different foliar fertilizer formulations and a wider range of plant nutrients would improve the generalizability of these findings and provide greater insight into the mechanisms underlying crop responses.

CONCLUSION

Our study demonstrated that foliar fertilization improved rice growth, nutrient uptake, and productivity relative to the unfertilized control, confirming its potential to alleviate nutrient limitations under low-input conditions. Foliar fertilization (FF) alone enhanced grain yield and nutrient acquisition, indicating that it can serve as an effective supplemental nutrient source. However, the combined application of foliar fertilizer with the recommended rate of inorganic fertilizer (IF+FF) did not produce significant improvements over inorganic fertilizer (IF) alone across the major productivity and nutrient uptake responses evaluated. These findings suggest that the recommended IF regime likely supplied sufficient nutrients to satisfy crop demand, thereby limiting the additional contribution of foliar-applied nutrients. Once nutrient requirements are adequately met through soil fertilization, crop nutrient uptake and biomass production become increasingly regulated by physiological demand, nutrient use efficiency, and sink capacity rather than by further nutrient inputs. Consequently, foliar fertilization may provide limited additional benefits under conditions of adequate soil fertility and optimal nutrient management. Nevertheless, the consistently higher numerical values observed under the IF+FF treatment indicate that foliar fertilization may still exert subtle physiological effects that were not detected statistically under the conditions of this study. Therefore, further investigations under contrasting soil fertility levels, environmental stresses, fertilizer application timings, and foliar formulations are warranted to elucidate the mechanisms governing crop responses and to identify conditions under which foliar fertilization can provide measurable agronomic benefits beyond those achieved with recommended IF alone.

DATA AVAILABILITY

The datasets used or analyzed during the current study are available from the corresponding author upon reasonable request.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the Agricultural Experiment Center, Central Mindanao University for their approval, support, area provision and facilitation of this study.

AUTHOR CONTRIBUTIONS

Junesa U. Cristobal: Conceptualization (Lead), Methodology (Lead), Data Curation (Lead), Formal Analysis (Lead), Investigation (Lead), Writing - Review and Editing (Lead), Resources (Lead); Apple Mae R. Canatoy: Methodology (Lead), Data Curation (Lead), Formal Analysis (Equal), Investigation (Equal), Writing - Review and Editing (Lead), Resources (Equal); Irish C. Achondo: Data Curation (Equal), Formal Analysis (Equal), Investigation (Equal), Writing - Review and Editing (Lead), Resources (Equal); Ronley C. Canatoy: Conceptualization (Lead), Methodology (Lead), Writing- Original Draft (Lead), Supervision (Lead), Validation (Lead), Software (Lead), Visualization (Lead).

CONFLICT OF INTEREST

The authors declare that they hold no competing interests.

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