Sustainable Soil Amendment with Basalt Powder: Unveiling Integrated Soil–Plant Responses in Ilex paraguariensis Cultivation

Abstract

As a sustainable alternative to conventional fertilizers, rock dusting is an emerging agroecological strategy to improve soil health and nutrient availability. This study aimed to quantify the effects of basalt powder (BP) application on the chemical attributes of a Ferralsol and the morphological responses of young Ilex paraguariensis (yerba mate) plants. The experiment was conducted in a randomized block design with five BP doses (0, 3.8, 7.6, 15.2, and 30.4 Mg ha⁻¹), where resulting soil and plant parameters were statistically analyzed. Results demonstrated that BP significantly increased available calcium, magnesium, and silicon in the soil (p ≤ 0.05) without altering pH or potassium levels. This soil enrichment directly correlated with a significant increase in the number of leaves per plant (p ≤ 0.01), which was strongly associated with soil Mg²⁺ (r = 0.73) and Si (r = 0.40). However, no significant effects were observed on plant height or stem diameter. We conclude that basalt powder acts as an effective slow-release source of Ca, Mg, and Si, primarily stimulating leaf development rather than immediate plant structural growth. This finding is consistent with the gradual nutrient release from silicate rocks and suggests that BP is a viable tool for enhancing soil fertility in yerba mate systems, although long-term evaluation is essential to understand its full agronomic potential.

1. Introduction

The growing demand for more sustainable agricultural systems has driven the search for alternatives to highly soluble synthetic fertilizers, whose intensive use is associated with high costs, dependence on non-renewable resources, and potential negative environmental impacts [1,2,3,4]. In this context, soil remineralization through the application of rock powders, a practice known as rock dusting, emerges as a promising agroecological strategy [5]. This technique aims not only to provide nutrients to plants but also to improve long-term soil health by utilizing mining byproducts in a circular economy model [6,7].

Yerba mate (Ilex paraguariensis A. St.-Hil.) is an arboreal species native to South America, of great social, economic, and cultural relevance, especially in Brazil, Argentina, and Paraguay. Its leaves are the raw material for popular beverages like chimarrão and tereré, and the industry has increasingly explored its bioactive compounds for the food and pharmaceutical sectors [8]. Traditionally cultivated in shaded agroforestry systems, the expansion of its cultivation to full-sun monocultures aims for higher productivity but also exposes plants to abiotic stresses and intensifies nutrient demand, making soil fertility management a critical factor for production sustainability [9,10].

The soils where yerba mate naturally thrives are generally acidic and have low availability of essential nutrients. The pursuit of more sustainable agricultural practices has spurred interest in alternatives to highly soluble synthetic fertilizers, which can have high costs and adverse environmental impacts. In this context, the application of rock powders as a source of nutrients and soil conditioner appears as a promising strategy [11]. Among the various materials used in rock dusting, basalt stands out. In powder form, as a mining byproduct, it is rich in minerals that, upon weathering in the soil, can gradually release nutrients such as calcium (Ca), magnesium (Mg), potassium (K), and silicon (Si), in addition to essential micronutrients [7,12,13,14].

Recent studies have demonstrated the potential of basalt powder to improve soil health in various agricultural systems [15,16,17,18,19,20]. Research indicates that its application can increase available nutrient contents, raise pH, improve soil aggregation, and increase organic carbon stock, thereby increasing the resilience of the agricultural system [14,17,21]. In crops such as corn and rice, basalt powder application resulted in significant improvements in soil fertility and nutrient accumulation in plants [22,23].

Despite the proven benefits of basalt powder in various annual and perennial crops, there is a gap in scientific knowledge regarding the effects of using this input in yerba mate cultivation. The response of a perennial species adapted to acidic soils to this management practice is unknown, especially regarding the long-term impacts on soil chemistry and plant nutrient absorption.

Given the above, the hypothesis of this work is that the application of basalt powder, by promoting the gradual release of cations like Ca²⁺ and Mg²⁺ and the beneficial element Si, will improve soil chemical fertility indicators and, consequently, stimulate the vegetative development of young yerba mate plants. Thus, the objectives of this work were: To quantify the effects of increasing doses of basalt powder on the chemical attributes (pH, available Ca²⁺, Mg²⁺, K⁺, and Si) of a Ferralsol cultivated with yerba mate; to evaluate the biometric response of young yerba mate plants to the basalt powder application; and to investigate the correlations between changes in soil attributes and plant growth variables in order to provide subsidies for the development of more sustainable fertilization practices for the crop.

2. Materials and Methods

2.1. Experiment Location and Soil and Basalt Powder Characterization

The experiment was conducted in an experimental area located in the municipality of União da Vitória, Paraná state, Brazil, under geographical coordinates 26°18′8.17″ S and 51°11′28.34″ W, with an average altitude of approximately 1005 m (Figure 1). The region’s climate is temperate, with mild summers (Cfb according to Köppen). Rainfall is uniformly distributed, with no dry season, and the average temperature of the warmest month does not reach 22 °C. The soil in the study area was classified as a Ferralsol, according to the World Reference Base for soil resources [24]. Subsequently, it was subjected to physical and chemical classification following the methodology described by Teixeira et al. [25]. For this purpose, soil sampling was performed at a depth of 0–20 cm, with one composite sample formed by 10 subsamples collected randomly across the experimental area. After collection, soil sample was air-dried, sieved through a 0.5 cm mesh, and then prepared for laboratory analysis.

For chemical characterization, samples were oven-dried with forced air circulation at 45 °C to constant weight, ground, and passed through a 2 mm sieve. Soil pH was determined potentiometrically in a soil:0.01 mol L⁻¹ CaCl₂ solution suspension at a 1:2.5 ratio. Organic matter was determined by oxidation with K₂Cr₂O₇ in an acid medium (H₂SO₄). The contents of Al³⁺, Ca²⁺, and Mg²⁺ were extracted with 1 mol L⁻¹ KCl solution and quantified by atomic absorption spectrometry (AAS). Phosphorus (P) and potassium (K⁺) were determined by ion-exchange resin extraction, with potassium quantified by flame photometry and phosphorus by colorimetry [26]. The resins consisted of mixed-bed anion- and cation-exchange beads, which simulate nutrient uptake by plant roots and are widely adopted for tropical soils in Brazil. Although Mehlich III is the standard method used by SSSA in the United States and other regions, studies have shown that resin extraction provides more reliable estimates of available nutrients in highly weathered soils, where Mehlich III may overestimate nutrient availability [27,28]. Soluble silicon was extracted with 0.01 mol L⁻¹ CaCl₂ solution and determined by the molybdenum blue method [29]. Sum of bases (SB = Ca²⁺ + Mg²⁺ + K⁺) and potential cation exchange capacity (CEC = SB + H⁺ + Al³⁺) were calculated based on the obtained results (

Table 1. Chemical attributes of the composite soil sample used in the experiment (0–20 cm).

SOM 1	pH	P	S	K+	Ca2+	Mg2+	Al3+	H + Al	CEC 2	BS 3
g dm−3	(CaCl2)	- mg dm−3 -		-------------------- cmolc dm−3 --------------------						%
52.1	4.10	4.00	13.00	0.09	0.70	0.41	2.0	10.8	12.0	10

¹ SOM = soil organic matter; ² CEC = cation-exchange capacity; ³ BS = base saturation.

).

In addition to chemical attributes, the soil was also physically characterized before the treatments were applied. The Ferralsol presented a clay texture (76.4% clay, 17.8% silt, and 5.8% sand) and a bulk density of 1.22 g cm⁻³. These properties are important to highlight, since soil texture and density directly affect nutrient retention, mobility, and the overall efficiency of remineralizer application in tropical soils.

The basalt powder used originated from a crushed rock mining company located in the municipality of Paula Freitas, Paraná, Brazil (26°11′4.51″ S; 50°56′54.36″ W–WGS84) (Figure 1). Its chemical composition was determined by X-ray fluorescence (XRF) at the Laboratory of Mineral and Rock Analysis of the Federal University of Paraná (

Table 2. Chemical composition of basalt powder determined by X-ray fluorescence (XRF).

SiO2	Al2O3	CaO	Fe2O3	K2O	MgO	MnO	P2O5	Na2O	TiO2	LOI 1
------------------------------------------------------ % ------------------------------------------------------
51.83	12.86	10.26	14.31	0.79	6.29	0.21	0.17	2.22	1.32	0.38

¹ LOI—loss on ignition (structural volatiles).

). The levels of potentially toxic elements conformed to Brazilian legislative limits [30], with measured concentrations of arsenic (As) < 1.0 mg kg⁻¹, cadmium (Cd) < 1.0 mg kg⁻¹, lead (Pb) 39.0 mg kg⁻¹, and mercury (Hg) < 0.1 mg kg⁻¹.

Petrographic mineralogical analysis indicated a typical composition of tholeiitic basalts from the Paraná Basin, composed of volcanic glass, diopside (pyroxene), labradorite (plagioclase), and opaque iron and titanium oxide minerals (

Table 3. Mineralogical characterization of basalt powder by petrographic analysis.

Labradorite	Diopside	Opaque Minerals	Secondary Iron Oxides	Sericite	Volcanic Glass
-------------------------------------------------------- % --------------------------------------------------------
45.0	40.0	10.26	traces	traces	10

). The grain-size analysis showed that the entire sample (100.00% ± 0.1) passed through both 2.00 mm and 0.840 mm sieves. Furthermore, 52.0% (±0.7) of the sample passed through a 0.300 mm sieve, and 22.0% (±0.4) passed through a 0.075 mm sieve. Based on the grain-size distribution, a reactivity of 87% was calculated [30], indicating that most of the basalt powder was concentrated in finer fractions (<0.3 mm), which are more reactive due to their larger surface area and greater potential to release nutrients through weathering.

2.2. Area Preparation and Treatment Implementation

Initially, experimental plots were demarcated. The planting of Ilex paraguariensis seedlings occurred on 10 September 2023, with a spacing of 3.0 m between rows and 1.5 m between plants. Each plot consisted of four 9 m rows, totaling 28 plants per experimental unit. The seedlings, sourced from a specialized nursery, exhibited uniform morphological patterns and underwent standardized weed management.

Before planting, pits with dimensions of 20 cm in width by 20 cm in depth were opened. The basalt powder doses, as detailed in item 2.3, were applied directly into the pits, followed by the insertion of the seedlings and covering with soil.

2.3. Experimental Design and Treatments

A randomized block design was adopted, comprising five treatments and four replicates, totaling 20 plots. Treatments consisted of applying basalt powder doses calculated to raise the Ca²⁺ content to critical levels, based on the initial soil chemical characterization (Table 1). The applied doses corresponded to 0, 3.8, 7.6, 15.2, and 30.4 Mg ha⁻¹ (

Table 4. Description of experimental treatments with increasing doses of CaO and basalt powder.

Treatment	Dose x Ca2+	Dose of CaO (kg ha−1)	Doses of Basalt Powder (Mg ha−1)
1	0	0	0
2	0.5	390	3.8
3	1	780	7.6
4	2	1560	15.2
5	4	3120	30.4

).

2.4. Soil and Plant Sampling and Analyses

Twenty-two months after planting, soil samples were collected from the 0–20 cm layer, with composite samples consisting of 10 subsamples extracted 20 cm from the trunk of representative plants. The following chemical attributes were evaluated: pH in CaCl₂, and available contents of K⁺, Ca²⁺, Mg²⁺, and Si. Analyses followed the methods described by Teixeira et al. [25] and Raij [26] as detailed in item 2.1.

Simultaneously, 10 plants per plot were evaluated for biometric variables: height (cm), stem diameter (mm), and leaf count. Measurements were performed using a graduated ruler and digital caliper.

2.5. Statistical Analyses

Initially, data were subjected to normality (Shapiro-Wilk) and homogeneity of variances (Levene’s) tests. After confirmation of assumptions, each soil and plant variable was analyzed separately using analysis of variance (ANOVA). In the model, basalt powder doses were considered fixed effects, whereas experimental blocks were included as random effects. When significant differences were detected, polynomial regression models were fitted to describe dose–response relationships. Pearson’s correlation coefficients were used to assess associations between soil attributes and plant biometric traits, with the necessary caution that correlations only indicate statistical relationships and not causality. Principal Component Analysis (PCA) was further applied to synthesize the multivariate response patterns.

All statistical analyses were conducted in Python language (version 3.11), utilizing the pandas, statsmodels, scikit-learn, seaborn, and matplotlib packages.

3. Results

3.1. Effects on Soil Chemical Properties

The application of basalt powder significantly altered the soil’s chemical attributes 22 months after its incorporation (

Table 5. F-values from ANOVA test for soil chemical attributes after basalt powder application.

Soil Attributes	Shapiro-Wilk (p-Value)	Levene (p-Value)	SV	DF	F-Value
pH	0.42	0.86	Dose	4	1.45 ns
			Block	3	1.61 ns
K+	0.10	0.82	Dose	4	1.18 ns
			Block	3	0.96 ns
Ca2+	0.62	0.81	Dose	4	12.67 **
			Block	3	4.39 *
Mg2+	0.69	0.56	Dose	4	6.86 *
			Block	3	0.65 ns
Si	0.43	0.57	Dose	4	4.86 *
			Block	3	2.16 ns

SV = Source of variation; DF = Degrees of freedom; F value = Observed F statistic value; ** significant at p ≤ 0.01, * significant at p ≤ 0.05, ns not significant by F-test.

). An analysis of variance (ANOVA) revealed a significant treatment effect on the available contents of calcium (Ca²⁺), magnesium (Mg²⁺), and silicon (Si) (p ≤ 0.05). In contrast, soil pH (in CaCl₂) and available potassium (K⁺) contents were not significantly influenced by the basalt application rates (p > 0.05). The statistical assumptions of normality (Shapiro-Wilk test) and homogeneity of variances (Levene’s test) were met for all analyzed variables.

Regression analysis was employed to quantify the dose–response relationships for the soil attributes (Figure 2). Available Ca²⁺ contents exhibited a complex positive response to the applied doses, with the model yielding a coefficient of determination (R²) of 0.81. Similarly, available Mg²⁺ and Si contents increased with higher application rates, fitting regression models with R² values of 0.76 and 0.94, respectively. The mean values for soil pH and K⁺ remained constant across all treatments, averaging 3.94 and 0.09 cmol_c dm⁻³, respectively.

3.2. Biometric Response of Yerba Mate

Regarding the biometric variables of yerba mate, ANOVA revealed that only the number of leaves per plant was significantly influenced by the basalt treatments (p ≤ 0.01) (

Table 6. F-values from ANOVA test for yerba mate biometric characteristics.

Plant Attributes	Shapiro-Wilk (p-Value)	Levene (p-Value)	SV	DF	F-Value
Height	0.68	0.60	Dose	4	2.09 ns
			Block	3	0.81 ns
Diameter	0.67	0.86	Dose	4	1.71 ns
			Block	3	2.29 ns
Number of leaves	0.45	0.91	Dose	4	5.85 **
			Block	3	0.44 ns

** significant at p ≤ 0.01, ns not significant by F-test.

). Plant height and stem diameter showed no statistical response to the different application rates.

The number of leaves per plant was best described by a quadratic polynomial regression model (Figure 3), which yielded a high coefficient of determination (R² = 0.92). This model indicates that leaf number increased with the initial application rates, reaching a maximum at intermediate doses before leveling off. Conversely, neither plant height nor stem diameter fitted a significant regression model, with their mean values recorded at 26.68 cm and 0.3764 mm, respectively.

3.3. Plant-Soil Relationships

Pearson’s correlation matrix elucidated the associations between soil properties and plant biometric traits (Figure 4). The number of leaves, the most responsive plant variable, demonstrated a strong positive correlation with soil Mg²⁺ content (r = 0.73). Moderate positive correlations were also observed between leaf number and the contents of Ca²⁺ (r = 0.41) and Si (r = 0.40). Furthermore, plant height was positively correlated with soil Mg²⁺ (r = 0.53).

Principal Component Analysis (PCA) successfully synthesized the multivariate data structure, with the first two principal components (PC1 and PC2) accounting for 70.33% of the total variance (50.01% and 20.32%, respectively). The PCA biplot (Figure 5) showed a clear separation of treatments along the first axis. The higher basalt doses were distinctly grouped on the right side of the plot and were positively associated with the loading vectors for Ca^2+, Mg²⁺, Si, and, most notably, the number of leaves. This multivariate analysis reinforces the direct link between the soil chemical changes induced by the remineralizer and the stimulation of leaf development in yerba mate.

4. Discussion

4.1. Gradual Nutrient Release and Impacts on Soil Chemistry

The application of basalt powder as a soil remineralizer led to a significant enhancement of available Ca²⁺, Mg²⁺, and Si in the soil (Figure 2). This outcome is a direct consequence of the source material’s chemical and mineralogical composition, which is rich in primary minerals such as labradorite (a Ca-rich plagioclase) and diopside (a Ca- and Mg-rich pyroxene), collectively constituting 85% of the basalt [17,18,31]. The weathering of these silicate minerals, though inherently slow, was effective in releasing these cations to the soil’s exchange complex, thereby acting as a long-term fertilizer source [7,32]. This behavior aligns with previous studies demonstrating the capacity of silicate rocks to supply nutrients gradually over time [7,14,15,19,31,33,34,35,36].

Notably, no significant change in soil pH was observed within the 22-month timeframe (Figure 2). This finding is consistent with the known geochemistry of silicate minerals, whose acid-neutralizing capacity is considerably slower and less potent than that of traditional carbonate liming materials. The consumption of protons (H⁺) during silicate dissolution is a gradual process, and in highly buffered soils such as the Ferralsol in this study, a period exceeding 2 years is often required to detect a significant corrective effect [37,38]. Similar results were reported by Luchese et al. [31], who observed no short-term alteration of soil pH after basalt application in tropical Oxisols despite increases in Ca and Mg availability. Likewise, Manning et al. [1] highlighted that basalt powders act as slow-release sources of base cations, with liming effects becoming evident only in the medium to long term, especially under high rainfall conditions typical of subtropical and tropical regions.

The improvement in soil fertility without a concurrent rise in pH is particularly relevant for forest ecosystems and crop species adapted to naturally acidic soils, such as Ilex paraguariensis. Unlike conventional liming materials, which can substantially alter soil chemistry and disturb native microbial communities, basalt allows for the maintenance of moderate acidity while supporting natural nutrient cycling, thereby preserving soil ecosystem functionality [9]. Consistent with this, Conceição et al. [34] demonstrated that basalt application enhanced nutrient supply in maize and bean plantations without disrupting the acid–base equilibrium of the soil, reinforcing its suitability for perennial systems.

The lack of response in available K⁺, despite its presence in the parent rock (0.79% as K₂O), can be attributed to its inclusion in more resistant mineral phases [16] and its high mobility in low-CEC soils, where it is susceptible to leaching, especially amidst the increased concentration of competing divalent cations like Ca²⁺ and Mg²⁺ [39]. Beyond fertility, these changes may also influence soil resilience and carbon sequestration processes, given the buffering effect of basalt weathering [40]

An additional aspect that merits attention concerns the Pb concentration detected in the basalt powder (39 mg kg⁻¹). This value is below the maximum allowed by Brazilian legislation for soil conditioners [30] and is within safe agronomic limits. Moreover, Pb in basalt is mostly bound to resistant oxides and silicates, which considerably reduces its solubility and plant availability [41,42]. Nevertheless, future studies should include monitoring of Pb in soils and Ilex paraguariensis tissues to ensure food safety and to provide comprehensive risk assessments.

Another relevant aspect concerns the grain size distribution of the applied basalt powder. Although 52% of the material passed through a 0.3 mm sieve, a considerable fraction remained between 0.3–2 mm, which represents relatively coarse particles. These coarser fractions are less reactive and weather at a much slower rate compared to fine powders (<0.3 mm), as widely reported in the literature [34,43]. This characteristic may explain the absence of rapid effects on soil pH and K⁺ availability, since the dissolution of resistant mineral phases is a long-term process. Therefore, the observed responses in Ca²⁺, Mg²⁺, and Si availability can be interpreted as an early indication of basalt reactivity, but more pronounced effects are expected to emerge only in the medium to long term, as finer and intermediate particles gradually weather and release nutrients.

4.2. Biometric Response and Resource Allocation in Yerba Mate

The response of yerba mate to basalt application was highly specific, manifesting as a significant increase in leaf number without a corresponding effect on plant height or stem diameter (Figure 3). This selective response pattern is characteristic of perennial species during their establishment phase. In these early stages, plants typically prioritize the allocation of photoassimilates to the root system to ensure long-term survival and resource acquisition, rather than investing heavily in above-ground vegetative growth [44]. Consequently, growth responses in height and biomass in perennial crops treated with slow-release fertilizers are often delayed, becoming apparent only after several years of application.

The targeted stimulation of leaf production is strongly linked to the observed improvements in soil nutrition (Figure 4). The robust positive correlation between leaf number and soil Mg²⁺ (r = 0.73) is particularly telling, as magnesium is the central atom of the chlorophyll molecule and is thus indispensable for photosynthesis and the generation of new foliar tissue [45]. Furthermore, although not classified as an essential element, silicon provides substantial benefits by accumulating in the leaf epidermis, which enhances plant architecture, light interception, and resistance to both biotic and abiotic stresses [46]. The increased availability of Si and its positive correlation with leaf number (r = 0.40) suggest an additional mechanism by which basalt application may have contributed to the health and persistence of the plant canopy.

Additional evidence supporting our findings comes from recent studies showing that mineral amendments derived from silicate rocks often produce early changes in foliar development and physiological status before noticeable increases in stem height or basal diameter in perennial or slow-growing systems. For example, field and nursery studies using basalt or other silicate rock powders reported improvements in initial vigor, leaf area, or leaf nutrient status in seedlings and young plants [17,34], as well as increased tillering/leaf production in forage species [7] and early agronomic benefits in annual trials [19]. Mechanistically, these responses have been associated with greater Mg availability, enhancing chlorophyll synthesis and photosynthetic capacity [45], and with Si accumulation improving leaf tissue robustness and stress tolerance [46]. Likewise, studies on perennial root allocation emphasize that young perennials prioritize belowground establishment and root functional traits in the first seasons, delaying large investments in stem elongation [44]. Altogether, these reports corroborate our interpretation that basalt powder promotes nutritional improvements that first manifest as enhanced foliar development, and that structural growth responses may require longer periods to become statistically evident in Ilex paraguariensis.

4.3. Multivariate Synthesis and Implications for Sustainable Management

The multivariate analyses provided a holistic view that integrated the individual soil and plant responses, reinforcing the cause-and-effect relationship between basalt application and plant performance (Figure 5). The PCA effectively demonstrated that the changes in soil chemistry—specifically the enrichment in Ca, Mg, and Si—were the primary drivers of variation among treatments and that this chemical shift was directly aligned with the vector for increased leaf number. This illustrates that even before substantial gains in stem biomass are realized, nutritional enrichment of the soil translates into a positive physiological response, creating the potential for enhanced photosynthetic capacity. The use of such multivariate methods, therefore, proved to be an essential complementary tool for interpreting complex agronomic responses.

These integrated soil–plant patterns are consistent with findings from recent field and pot studies using basalt powder and crushed basalt amendments, which report initial increases in plant-available Ca, Mg, and Si following basalt application and corresponding early agronomic responses (e.g., enhanced leaf production or biomass) in several crops and soil types [17,22]. For example, in a greenhouse experiment, Luchese et al. [47] found that basalt powder increased soil calcium (Ca) and phosphorus (P) content, leading to improved dry matter accumulation in maize and soybean, while multi-site experiments in temperate and tropical conditions have found early increases in Ca and Mg pools and positive crop responses after basalt application [19,21].

From a management perspective, the PCA results support the notion that basalt powder acts primarily as a multinutrient remineralizer that modifies the soil chemical environment in predictable ways—improving base saturation and increasing Si availability—which can translate into improved vegetative development for perennial species such as Ilex paraguariensis over medium-to-long time frames. These emergent patterns align with reviews and meta-analyses that highlight site-specific outcomes for rock–dust amendments and emphasize the need to integrate mineralogy, particle size, soil texture, and cropping system into recommendations [48,49]. Therefore, our multivariate findings not only corroborate recent empirical results but also reinforce the recommendation to monitor responses over multiple years and to couple basalt powder application with complementary management (e.g., cover crops, organic matter inputs) to maximize nutrient retention and agronomic benefits.

Beyond its agronomic role, the application of basalt powder also carries important environmental implications related to the global carbon cycle. Through the process of enhanced weathering, the dissolution of silicate minerals in basalt consumes atmospheric CO₂, leading to the formation of stable bicarbonates that can eventually be transported to oceans, where they precipitate as carbonates [50]. This mechanism has been increasingly recognized as a natural pathway to sequester CO₂ while simultaneously improving soil fertility. In highly weathered tropical soils, where leaching rates are high, the gradual release of cations such as Ca²⁺ and Mg²⁺ from basalt may accelerate this process, coupling nutrient cycling with carbon capture [43]. Therefore, basalt powder amendments can be framed not only as a strategy for sustainable fertilization but also as a nature-based solution that contributes to climate change mitigation, reinforcing their multifunctional value in agroforestry systems such as Ilex paraguariensis cultivation.

4.4. Synthesis and Future Perspectives

The results of this 22-month study demonstrate that basalt powder acts as an effective slow-release source of Ca, Mg, and Si for the soil. In this initial stage, the nutritional enrichment translated into a significant increase in the number of leaves on young yerba mate plants. The absence of immediate effects on height and diameter growth is consistent with the characteristically slow resource allocation to above-ground parts in perennial crops and with the nutrient release kinetics of silicate rocks. Similar findings have been reported in other crops, where nutrient release from basalt is gradual and strongly influenced by soil mineralogy and climate [1,51].

In this context, basalt powder application emerges as a promising regenerative soil management practice, capable of enhancing baseline fertility in perennial forest systems, reducing reliance on synthetic inputs, and supporting ecosystem services such as soil biodiversity conservation, organic carbon stabilization, and productive resilience to climate variability. When applied to silvicultural or agroforestry systems involving native species like Ilex paraguariensis, basalt remineralization may contribute simultaneously to ecological intensification and sustainable rural development in tropical regions.

From an environmental perspective, the relatively low levels of potentially toxic elements in the basalt powder used in this study are encouraging. Nevertheless, systematic monitoring of heavy metals such as Pb remains essential, particularly when targeting long-term application in food production systems [52]. Incorporating such assessments will contribute to the broader acceptance of silicate rock remineralizers as safe inputs in agroforestry systems.

Thus, this work provides the first evidence of the potential of rock dusting as a sustainable fertilization practice for yerba mate. To advance this knowledge and optimize the practice, future research should focus on: (i) long-term monitoring to assess the cumulative effects on soil acidity neutralization and final yield; (ii) foliar analysis to quantify the uptake and accumulation of nutrients released from the rock; (iii) evaluating the impact on the phytochemical quality of yerba mate leaves; and (iv) investigating synergies with organic management practices, such as the addition of organic matter or microbial inoculants, which could potentially accelerate rock weathering. Such studies will be crucial not only for the yerba mate crop but also for solidifying rock dusting as a tool within the circular economy, thereby enhancing the resilience and sustainability of agroecosystems. Furthermore, the integration of rock dust into yerba mate systems may contribute to sustainable nutrient management and align with global efforts to reduce dependence on synthetic fertilizers [7].

5. Conclusions

The application of basalt powder significantly increased the available calcium, magnesium, and silicon contents in the soil without causing changes in pH. These results confirm the hypothesis that basalt acts as a source of essential nutrients through the gradual remineralization of its mineral constituents, even under high leaching edaphoclimatic conditions.

An increase in leaf count was observed in response to intermediate doses of the remineralizer, accompanied by a strong correlation with mobilized soil nutrients. The absence of a response in potassium suggests limitations in its release rate or high mobility within the soil profile, indicating a need for complementary management strategies.

Multivariate analysis revealed consistent patterns of integrated plant–soil response, indicating that basalt powder application contributes to improved chemical conditions and may promote more evident agronomic effects in the medium and long term.

Given the results obtained, continuous monitoring of rock dust effects in yerba mate systems over full production cycles is recommended, as well as evaluating its interaction with complementary fertilization practices, aiming to maximize the agronomic efficiency of the remineralizer in tropical contexts.