The research was conducted at the Ciliwung Tea Plantation in Cisarua District, Bogor Regency, West Java Province, Indonesia, from November 2023 to March 2024. Figure 1 shows the distributions of soil sampling sites within the Ciliwung Tea Plantation, located at approximately 6° 41' 00” S and 107° 00' 00” E. The research site has an elevation ranging from 1,363 to 1,560 meters above sea level (m asl). This study employed descriptive statistics to summarize and interpret the soil property data collected from the sampling sites.

Climate data for the research location were obtained from the Bogor Regency Statistics Agency covering the period from 2010 to 2023 (BPS, 2023). The study site exhibits a humid tropical climate characterized by an annual precipitation of 3,164 mm. The rainy season extends from October to May, featuring peak average rainfall in February at 500.7 mm month^-1, while July and August record the lowest rainfall, approximately 90.3 mm month^-1 and 92.1 mm month^-1, respectively (Fig. 2). The mean temperature at the study site varies between 24 to 25 °C. No significant temperature variations occur between the rainy and dry seasons (Fig. 2). In the rainy season, the research site exhibits air humidity levels ranging from 84–89%, whereas in the dry season, these levels drops to between 80–79%. Air humidity peaks in January and February, whereas it reaches its lowest levels in August and September (Fig. 2).

The parent material at the study site is identified based on the geology map of Bogor, utilizing secondary data from Effendi et al. (1998). The geological map indicates that the research area is composed of parent rock material, specifically andesite and andesite breccia. The parent material identified in the study was andesitic tuff rock.

The study was conducted in four designated blocks (C-4, C-9, C-10, and C-12) within the tea plantation area (Fig. 1), encompassing an area of 98 ha. Soil profile observations and soil sampling were performed in each block. This study utilized four vertical soil profile samples, composite soil samples collected from 10 points surrounding the soil profile observation, and ring soil samples taken from the top layer of the soil profile. Four soil samples were selected according to varying tea health conditions (vigor), aspect, elevation, and slope position. The health conditions of the tea plants were categorized as follows: healthy tea plants on slopes of 3-8% (P1) and 30-40% (P4), rejuvenated healthy tea plants on slopes of 8-15% (P2), and unhealthy tea plants on slopes of 8-15% (P3). The samples comprised those taken from each layer of the soil profile, composite soil samples (disturbed), and soil samples from rings (undisturbed). All soil samples were analyzed using various methods, reflecting the differing vigor of tea plants.

Soil profiles were constructed with dimensions of 2 m in length, 1 m in width, and 1.5 m in depth; however, variations in depth may occur depending on the presence of the C layer/parent material, as well as the specification of the soil order control section. The parameters observed in the soil profile consist of: solum depth, horizon boundaries, horizon thickness, plant rooting, field soil texture, soil color, soil structure, soil consistency, field soil pH, slope position, slope class, and elevation (Soil Survey Staff, 2022; Sukarman et al., 2017).

Composite samples were collected from the topsoil layer at depths of 0–20 cm and 20–40 cm at various locations, subsequently combined into a single sample with two repetitions. Composite sampling was used to acquire more representative soil chemical data. A ring sample, representing an undisturbed soil sample, has been collected from the topsoil at a depth of 0-20 cm. Table 1 presents methods for physical, chemical, and mineral analysis. Legacy soil data from published Wahyudin (1989) and Muslim et al. (2025). The data sites near the Ciliwung Plantation, assumed to be comparable, exhibit similar soil chemical values corresponding to tea plantations with equivalent land use. Table 1 presents various methods for physical, chemical, and mineral analysis. In addition, we analyzed the correlations between soil characteristics—including base saturation, cation exchange capacity (CEC), and organic C and N—and tea yield through Pearson correlation analysis.

The soil classification used in this study follows the outline in the USDA Soil Taxonomy book (Soil Survey Staff, 2022). The National Soil Classification System (Subardja et al., 2014) and World Reference Base for Soil Resources (WRB) by FAO (IUSS Working Group WRB, 2015) serve as equivalents.

The research site exhibited a deep solum, supported by four soil profiles, each exceeding 150 cm in depth, as indicated in Table 2. The depths were determined according to the deepest observable pedogenic horizon. All profiles exhibited dark brown topsoil (7.5YR 3/2 to 7.5YR 3/3) (Table 2), indicating a relatively elevated concentration of soil organic matter. Profile P1 exhibited greater color variation relative to other profiles, characterized by a significant darker horizon at a depth of 18 cm to 49 cm compared to the surface layer. The soil matrix exhibited colors varying from reddish dark brown to brownish yellow within the depth range of 49 cm to 129 cm. The observed reddish and yellowish colors indicate the presence of iron oxide minerals, such as hematite, goethite, and lepidocrocite. Yellowish hues were observed in subsoil layers at depths greater than 120 cm in additional profiles. The varied colors observed in profile P1 suggest a more developed soil formation, presumably linked to enhanced structural development relative to the other profiles. This is evidenced by its well-developed structure and significant clay accumulation, which is also indicated by its higher bulk density. Profile P3 exhibited a distinct contrast, characterized by a dark upper horizon and a lighter lower horizon (Fig. 3), indicative of variations in organic matter content. In wet conditions, soil consistency varied from slightly sticky to sticky in profiles P2, P3, and P4, whereas profile P1 exhibited a consistency ranging from sticky to very sticky, indicating a higher clay content. In moist conditions, the soil exhibited friability. The horizon boundaries across all profiles exhibited variability, ranging from distinct and gradual to diffuse and smooth.

The physical properties of all soil profiles are presented in Table 3. The values of bulk density (Bd) and particle density (Pd) exhibited an inverse relationship with total porosity. Bd exhibited low (0.58-0.73 g cm^-3) values, while total porosity is consistently high (63.25-68.55 %). Profile P1 exhibited the highest values of Bd and Pd, followed by P3, whereas P2 and P4 exhibited similar and comparatively lower values. Profiles P2 and P4, characterized by lower Bd and Pd, exhibited increased total porosity. In contrast, P1, with higher Bd and Pd, had the lowest total porosity.

Bd and Pd reflect the proportion of solid material within the soil, whereas total porosity represents the void present between soil particles. Bulk density and porosity variations are significantly influenced by the soil particle‐size distribution, or texture (Table 4a). P1 exhibited a higher bulk density and lower porosity due to its clay loam texture, which is characterized by a predominance of fine particles. P4 exhibited reduced bulk density and increased porosity attributed to its sandy loam texture, characterized by a higher proportion of coarse particles. In contrast, P2 and P3 exhibited a silty loam texture, indicating an intermediate condition relative to P1 and P4.

Fast aeration pores are characterized by larger pore spaces exceeding 28.8 microns in diameter, whereas slow aeration pores are defined by smaller pore spaces ranging from 8.6 to 28.8 microns. Table 3 indicates that profile P4 exhibited the highest percentage of fast aeration pores compared to all profiles. Conversely, profile P1, characterized by a higher Pd, exhibited a reduced percentage of fast aeration pores. Profile P3 exhibited the highest percentage of slow aeration pores, whereas profile P1 displayed the lowest percentage. The highest availability of water was observed in P2, succeeded by P3, P1, and P4.

The soil water retention curves (SWRC) presented in Figure 4 demonstrate notable variations in pore-size distribution and water holding capacity across the four pedons, which are critical factors influencing soil physical quality and crop productivity. All four pedons exhibited low bulk densities (0.58–0.73 g cm⁻^³) and high total porosities (63.25–68.55%), characteristics of volcanic andic soils abundant in amorphous minerals such as allophane and imogolite; however, their water dynamics varied considerably. The findings indicate that soil water availability is influenced more by pore architecture than by total porosity.

Pedon 2 (P2) demonstrated the highest volumetric water content at all matric potentials, achieving a plant-available water content (PAWC) of 17.10%. This indicates an optimal distribution of macropores and micropores, enhancing both drainage and water retention. The findings are consistent with earlier research indicating that well-aggregated soils characterized by moderate clay content and stable structure enhance soil water retention while maintaining adequate aeration (Dexter, 2004).

Conversely, Pedon 4 (P4), which demonstrated the highest total porosity at 68.55%, experienced significant water loss at higher matric potentials, resulting in the lowest PAWC of 12.45%. This suggests a prevalence of macropores and a coarser texture, facilitating infiltration and aeration while diminishing water storage capacity. This observation aligns with the findings of Jiang et al. (2020) and Harefa (2025) which indicate that coarse-textured soils exhibit greater susceptibility to drought stress.

Pedons 1 and 3 exhibited intermediate water retention curves (Fig. 4), with PAWC values of 16.55% and 16.60%, respectively, and aeration porosity greater than 18%. The characteristics indicate an advantageous soil structure and suitability for various cropping systems. The slope of the SWRC between pF 1 and pF 2.54 reflects gravitational drainage, whereas the stable water content observed at higher pF values (pF 2.54–4.2) in Pedons 1–3 implies efficient water retention in micropores.

These results underscore the necessity for tailored water management strategies at specific sites. Soils such as P4, characterized by high aeration and low water retention, may improve through practices that enhance micropore volume and organic matter content, such as biochar application, cover cropping, or residue mulching (Arif et al., 2021). P2 represents an ideal soil physical condition that can sustain intensive cropping systems while minimizing the risks of waterlogging or drought. The findings reinforce the necessity of integrating SWRC data with bulk density and porosity measurements in the assessment of soil physical quality, as no singular parameter can comprehensively represent the complexity of soil hydraulic behavior.

The SWRC analysis demonstrated significant variability in water retention across the pedons, indicating variations in soil texture, structure, and pore connectivity. Comprehending these variations is crucial for developing accurate water management and soil conservation strategies, particularly in regions prone to variable rainfall and drought risk. Future research should incorporate SWRC characteristics with hydraulic conductivity measurements and crop performance data to strengthen the relationship between soil physical properties and agricultural productivity.

The soils at the research site predominantly displayed loam textures, specifically clay loam, silty loam, and sandy loam. The soil pH was primarily acidic, exhibiting values from 4.5 to 5.5 (Table 4a). Very acidic conditions (pH < 4.5) were observed in the topsoil of profile P1 and in several composite soil samples, such as C1a, C1b, C2b, and C3b. C1a and C1b were collected in proximity to P1. Soil profile data revealed that subsoil layers exhibited higher pH values compared to the topsoil, indicating base leaching, likely influenced by the high annual rainfall at the study site (approximately 3,164 mm year^-1). Increased sum of exchangeable cations with soil depth indicate evidence of base leaching. The soil pH measured in KCl solution revealed potential acidity, exhibiting values lower than those recorded in distilled water (pH H₂O). The pH measurement with NaF indicated the prevalence of non-crystalline minerals, specifically allophane and imogolite.

The organic carbon content in all soil profiles and composite samples exhibited variation, with most; classified as high (3–5%) to very high (>5%) (Table 4a). The maximum organic carbon content in the topsoil was found in profiles P3 and P4, at 6.69%, whereas the minimum was recorded in P1, at 3.43%. The composite soil samples support these findings, displaying trends aligned with the profile data. The composite samples exhibited the highest organic carbon content in C2b (20–40 cm depth), located near P2, whereas the lowest values (2.8%) were observed in C1a and Cb, both near P1. Profile data indicated a significant reduction in organic carbon content in the subsoil relative to the topsoil, with the exception of P1, which retained a relatively high organic carbon level (3.0%) at a depth of 105 cm. The organic carbon content at comparable depths in P2 and P3 was significantly lower, record at 1.2% and 0.84%, respectively. The total nitrogen content in all samples was under 1%, except for the top layer of P3 and composite sample C2b, which exhibited N content of 1.16% and 1.06%, respectively (Table 4a). Nitrogen levels were strongly correlated with organic carbon, with more than 90% of the measured nitrogen existing in organic form. Both parameters indicate the organic matter content in the soil. The carbon-to-nitrogen (C/N) ratio indicates the relative amounts of organic carbon and nitrogen in the soil, where organic carbon levels consistently surpass those of nitrogen. A reduced C/N ratio indicates an accelerated release of nitrogen into the soil solution, thereby enhancing its availability for plant uptake (Brust, 2019). In this study, the majority of soil samples exhibited C/N ratios under 10. The highest C/N ratios were recorded in profile P1 (13–14) and in composite samples C3c and C3d (14–15). The lowest C/N ratio was recorded at 6, was found in the topsoil of profile P3 and in composite samples C2b and C3b.

The levels of exchangeable cations correlated with soil pH. The maximum exchangeable cation sum was recorded in profile P3, exhibiting a soil pH between 4.8 and 5.0. Profile P4, despite a higher subsoil pH of 5.6, demonstrated the lowest base cation levels across all profiles at comparable depths. The total exchangeable cations generally increased with soil depth, presumably as a result of cation leaching from the topsoil to the subsoil. Profile P4 displayed a distinct pattern, characterized by a decrease in exchangeable cation with depth. The location of P4 in a hilly area, coupled with dense tea vegetation and thick foliage, likely contributed to reduced rainfall infiltration and minimized leaching relative to the other profiles.Figure 5 illustrates that calcium (Ca) and magnesium (Mg) concentrations were comparable across samples, with the highest concentrations observed in profile P3 and the lowest in profile P4. Profile data indicated that potassium (K) concentrations were highest in P2 and lowest in P4. Sodium (Na) concentrations exhibited consistency across all samples, with the peak concentration recorded in the topsoil of P4 (Fig. 5).

The soil CEC observed in this study varied between 15 to 35 cmol kg^-1. Profile P1 exhibited the highest CEC values, ranging from 28.77 to 32.39 cmol kg^-1, whereas profile P4 exhibited the lowest values, ranging from 15.29 to 22.54 cmol kg^-1. The composite soil samples reflected a consistent trend, with the highest CEC observed in C1a, located near P1, and the lowest values found in C4a and C4b, located near P4.

The soils at the study site typically demonstrated low base saturation levels (<50%), which correlated with elevated soil acidity. The maximum base saturation occurred in profile P3 at depths of 18–82 cm, with values between 44% and 62%. Subsequently, profile P2 exhibited a value of 40% at depths ranging from 14 to 42 cm, whereas the composite sample C1b, recorded a value of 35%. In contrast, all other samples exhibit a base saturation value below 20%.

Volcanic soils are characterized by high phosphate retention (>85%). Table 4b indicates that all soil profiles exhibited phosphate retention exceeding 90%, with the exception of the subsoil in profile P3. While P1 was not assessed for phosphate retention, composite samples C1a and C1b, located near P1, may act as representative indicators of its phosphate retention capacity.

Oxalate-extractable Fe (Fe-ox) and Oxalate-extractable Al (Al-ox) signify the existence of these elements in non-crystalline mineral forms. Fe-ox levels varied between 0.43% and 4.63%, with the highest concentrations observed in the subsoil of profile P4, reaching 4.02% to 4.63% at depths of 46 to 155 cm (Table 4b). The subsoil of profile P3 exhibited the lowest Fe-ox concentration, measured, at 0.43% within the depth range of 124–170 cm. The levels of Al-ox exhibited a comparable pattern, as both Fe-ox and Al-ox are associated to non-crystalline minerals such as allophane and ferrihydrite.

The acidic nature of volcanic soils leads to elevated levels of Al^³⁺ and H⁺ saturation, particularly observed in profile P1 and composite samples C1a and C1b. In other areas, Al saturation was generally lower, as indicated by the comparatively low Al content in additional samples, especially in the surface layers. This condition is likely attributable to liming practices implemented in other blocks but not in P1, resulting in a pronounced disparity. The saturation levels of Al and H were inversely related to soil pH, with lower pH values indicating higher saturation of Al and H.

The effect of tea plantations in this area was assessed by employing a comparative approach, utilizing legacy soil data from sites near the Ciliwung Plantation, which was presumed to be similar (Table 5). Over 36 years, the Andosols of Bogor beneath tea plantations have experienced significant alterations in their chemical properties. A discernible trend of soil acidification was observed, with pH decreasing from an average of 5.26 in 1989 (W1–W2) to 4.93 in 2024 (P1–P4, N3). Substantial decreases were observed in soil organic matter (−46.6%), organic carbon (−46.6%), and CEC (−41.7%), indicating a weakening of the soil’s buffering capacity. These alterations align with prolonged leaching processes characteristics of humid tropical environments, further intensified by the ongoing use of acidifying nitrogen fertilizers in tea cultivation.

Base saturation increased from 7.7% to 18.0% during the same period; however, this increase does not signify an improvement in soil fertility. This indicates a relative increase resulting from the sharp decline in CEC. Consequently, while the percentage of exchange sites occupied by basic cations has risen, the total stock of nutrient cations has likely decreased or remained low. The total nitrogen content exhibited a slight increase from 0.24% to 0.35%, likely attributable to continuous fertilizer applications rather than an enhancement of soil organic matter reserves. These findings suggest that, despite ongoing nutrient inputs, the soil’s inherent capacity to store and regulate nutrients has been diminished.

The chemical degradation observed in these Andosols indicates progressive weathering and soil aging, likely involving the transformation of short-range order minerals into more crystalline phases with reduced charge densities. The observed trajectory, along with declining organic matter inputs and intensified acidification, highlights a sustained decline in soil quality and resilience within monoculture tea systems. The findings emphasize the necessity for restorative soil management practices, including organic matter enrichment, and balanced nutrient applications, to mitigate adverse trends and maintain the productivity of tea plantations on Andosols.

These changes indicate potential mineralogical shifts from short-range order minerals to more crystalline phases, signaling the onset of andic property deterioration. These transformations indicate that Andosols, previously considered resilient due to their high CEC and organic matter content, are actually susceptible to rapid degradation under intensive monoculture practices. The findings highlight the urgency for restorative management aimed at rebuilding organic matter, mitigates acidification, and preserving the distinctive andic properties essential for the productivity of tea plantation soils.

The sand fraction of the analyzed soils is primarily composed of rock fragments and weathered minerals (Table 6). Profile P1 exhibited the highest concentrations of weathered minerals and rock fragments, ranging from 22-29% and 49-60%, respectively. Small amounts of opaque minerals and quartz were identified, constituting less than <15% of the total composition. The presence of opaque minerals indicates that the analyzed soils originated from volcanic parent materials, whereas the low quartz content indicates that these soils have not experienced significant weathering or are still in the developmental stage. The analyzed soils contain easily weathered minerals, including labradorite, augite, and hypersthene, in small to moderate quantities. Profile P4 exhibited the highest concentrations of augite and hypersthene, ranging from 10-16% and 14-28%, respectively. The likely reason for this is that P4 has not experienced additional pedogenic development, leading to greater reserves of easily weathered minerals such as augite and hypersthene in comparison to other profiles. This interpretation is additionally reinforced by the comparatively limited structural development of P4 and its sand-dominated texture. The significant presence of these minerals indicates that the soil originated from intermediate andesitic or volcanic parent materials. The significant presence of weathered minerals and rock fragments, along with easily weathered minerals, illustrates the substantial nutrient reserves conducive to the growth and development of tea crops.

The mineral composition of the clay fraction in the analyzed soils exhibit considerable variability. Vermiculite is present in moderate quantities in Profiles P2 and P3, whereas illite is observed in small to very small quantities in Profiles P2, P3, and P4. Non-crystalline or amorphous minerals, meta-halloysite, gibbsite, quartz, goethite, and magnetite are present in small to moderate quantities. Hydrated halloysite minerals are present in limited quantities in Profile P1, whereas cristobalite is detected in minimal quantities in both Profiles P1 and P3 (Fig. 6).

Meta-halloysite was identified through XRD peaks exhibiting d-spacings of 0.713 to 0.722 nm (order 1) and 0.347 to 0.350 nm (order 2) following treatments with Mg²⁺, Mg²⁺ plus glycerol, and K⁺. Additionally, the peaks diminished after treatment with K⁺ and heating at 550 °C (Fig. 6). Hydrated halloysite exhibits a d-spacing of 1.000 nm (order 1) and 0.447 nm (order 2) following treatments with Mg²⁺, Mg²⁺ combined with glycerol, and K⁺. The peaks subsequently collapsed following K⁺ treatment combined with heating at 550 °C. Vermiculite exhibits a d-spacing of 1.423 nm after treatments with Mg²⁺, Mg²⁺ plus glycerol, and K⁺. The peaks collapse following a K⁺ treatment combined with heating at 550°C, yielding a d-spacing of 1.011 nm. XRD analysis revealed the presence of illite, characterized by d-spacing of 1.000 to 1.015 nm (order 1), and 0.540 to 0.545 nm (order 2). After treatment with Mg²⁺, Mg²⁺ plus glycerol, and K^+, gibbsite exhibits a d-spacing range from 0.482 to 0.489 nm. The peaks subsequently collapse following K⁺ treatment combined with heating at 550 °C. Cristobalite, quartz, goethite, and magnetite exhibit d-spacings of 0.404 to 0.406 nm, 0.334 to 0.339 nm, 0.255 to 0.256 nm, and 0.238 to 0.239 nm, respectively, following all treatments.

Climate is a significant factor influencing soil formation (Weil & Brady, 2016). Figure 2 presents the results of monthly climate data measurements for the period 2011-2022, derived from BPS data (BPS, 2023). The minimum air temperature was recorded in February at 24.4°C, while the maximum was observed in May at 26.5°C. The mean temperature throughout the entire duration was 25.0°C. The Braak (1929) equation was employed to determine the minimum temperature corresponding to the elevation of each soil profile, resulting in a range of 17.3–17.7°C, with in an average of 17.6°C. The soil temperature at the research site was estimated using the equation from van Wambeke (1982) (Eq. 1).

where: Ts is soil temperature and Ta is the annual average air temperature.

The estimated annual average soil temperature, according to the equation, is 20.1°C. This condition aligns with the isohyperthermic soil temperature regime as outlined by the Soil Survey Staff (2022).

February recorded the highest rainfall at 500 mm month^-1, while July and August experienced the lowest, with 90 mm month^-1 at 92 mm month^-1, respectively. The monthly average rainfall was 263.7 mm month^-1 leading to an annual average of 3,691.2 mm year^-1. The mean air humidity was 84.82%, with the peak recorded in January at 89.29% and the lowest in September at 79.47%. The research site exhibits an udic moisture regime (Soil Survey Staff, 2022).

The data indicated that the rainfall is classified as type A according to Schmidt and Ferguson (1951) classification system, characterized by a low ratio of dry months to wet months, with a Q value between 0.00 and 0.43. This indicates the absence of drought conditions for a duration of 90 consecutive days or longer at the research site. Ritung et al. (2011), highlight that tea plants thrive in temperatures ranging from 19 to 21°C, with annual rainfall between 2,500 and 4,000 mm, and air humidity below 70%. Ishak S et al. (2017) state that soil moisture is a crucial determinant of tea plant productivity, with an optimum humidity level of 87,2%. The climate conditions indicate that elevated rainfall contributes to the leaching of cations in the soil, attributed to high soil acidity levels at the research site.

The research site, as indicated on a 1:100,000 scale geological map of Bogor, Java, is situated within the breccia and lava formations of Mount Kencana and Mount Limo (Qvk). This area comprises Pleistocene-aged andesite and andesite breccia, such as andesine, labradorite, and hornblende, which are abundant in mineral nutrients (Effendi et al., 1998). Tan (1965) highlighted that Indonesian Andisols originated from diverse parent materials during the recent Pleistocene, predominantly consisting of andesitic tuffs.

The representative soil profile at the study site is situated in undulating to hilly terrain, with elevations ranging from of 1,430 to 1,496 meters above sea level and a slope class exceeding 3 to over 40% (Table 7). Slope gradient influences surface runoff. This process results in the depletion of organic matter in the topsoil layer and may lead to surface erosion, such as sheet erosion. Marianti et al. (2021) stated that elevation significantly affects soil properties, surpassing the impact of slope on factors, such as CEC, total N, available P, or exchangeable K, and bulk density. Values of organic carbon, total nitrogen, and available phosphorus exhibited an increase with ascending profile position and slope class (P4 > P3 > P2 > P1). Conversely, values of soil CEC, available potassium, and BD diminished. Soil CEC, an important measure of soil fertility, exhibited the highest value at the lowest slope and elevation, specifically in P-1 soil profile. Li et al. (2025) find that higher slopes exhibit greater total nitrogen and available nutrient values than lower slopes, whereas soil CEC is maximized on the middle slope. Table 7 presents the location of each representative soil profile in relation to the topographic conditions of the study site.

Soil classification refers to the procedure outlined in the methodology section. The study’s result classifies the soil according to the USDA Soil Taxonomy at the soil type level, identifying Alic Halpudands for soil profiles P-1, P-2, and P-3, and Acrudoxic Hapludands for soil profile P-4. As equivalents of the Soil Taxonomy, these soil types are classified as Andisol Distrik (soil profiles P-1, P-2, and P-3) and Andisol Okrik (soil profile P-4) in the National Soil Classification System. Meanwhile, in the FAO WRB system, they are classified as Dystric Alic Andosol and Dystric Acroxic Andosol.

The Pearson coefficient correlation between base saturation and yield is –0.056 (Table 8), suggesting an extremely weak and practically negligible association. A value near zero indicates that variation in base saturation does not significantly affect tea production. The CEC shows a correlation of 0.091 (Table 8), indicating a very weak association. This indicates that the soil’s capacity for cation retention and exchange is not a key factor influencing yield variation in the study area: rather, external factors such as microclimate, plant age, pruning intensity, or field management are likely to be more significant in determining productivity.

Soil organic carbon and nitrogen exhibit higher correlations with yield, recorded at 0.256 and 0.227, respectively. These values indicate weak relationships; however, they suggest a modest correlation between higher organic matter and nitrogen levels and increased production. This pattern corresponds with the functional roles of organic matter in enhancing soil structure, water retention, and nutrient availability, alongside the significance of nitrogen in promoting shoot growth in tea plants. Despite the low correlations, the impact of these soil properties on yield is minimal, indicating that productivity is primarily determined by agronomic practices and environmental conditions rather than the chemical soil characteristics assessed in this study.

This research focuses exclusively on the physiological analysis of plant tissue. We sought to acquire soil properties and establish correlation with plant vigor. This study examined soil characteristics across various layers of a selected soil profile, correlating them with the vigor of tea plants and their respective locations. The vigor of the tea plant in this study was assessed based on the physiological characteristic of the leaves at the apex, specifically their color and physical shape. Healthy tea plants exhibit leaves that range from light to dark green, characterized by a symmetrical, smooth, and uniform shape, devoid of any damage. Tea plants exhibiting poor health display a combination of dark and light green leaves, accompanied by yellowish and brownish patches resulting from pest and disease infestations, as well as wavy or curled leaf structures. Rejuvenated tea plants, resulting from pruning or rejuvenation, exhibit a light green coloration with predominantly bud-shaped leaves.