Multivariate assessment of soil fertility attributes in Alfisols of the central agro-climatic zone of Telangana, India

Introduction

Sustainable agricultural productivity in the semi-arid tropics of India is significantly hindered by soil fertility degradation [1] . Alfisols, which are prevalent across southern India, are inherently limited by low organic matter content, moderate nutrient-holding capacity, and a high susceptibility to nutrient imbalances, particularly under intensive cultivation [1,2] . In the Central Agro-Climatic Zone of Telangana, dominant cereal-based systems, such as rice and maize, place heavy nutrient demands on these fragile soils, further exacerbating inherent fertility constraints [3] . Soil nutrients and physicochemical properties operate as an interdependent system where processes like organic matter decomposition and nutrient fixation regulate overall availability to crops [1] . Because conventional univariate analyses often fail to capture these complex interactions, multivariate statistical techniques are increasingly utilized. While correlation analysis helps examine pairwise relationships, Principal Component Analysis (PCA) is particularly effective for reducing data dimensionality and identifying the dominant drivers of soil variability [4] . Recent studies have integrated PCA with geostatistical methods to delineate site-specific management zones (MZs), which have been shown to improve nutrient use efficiency and significantly increase yields in maize systems within Telangana [5] . However, comprehensive multivariate assessments focusing on Alfisols of the Central Agro-Climatic Zone of Telangana remain limited. Therefore, the objectives of the present study were to (i) characterize soil fertility status using descriptive statistics, (ii) examine interrelationships among soil properties through correlation analysis, and (iii) identify key soil fertility drivers using PCA for improved nutrient management strategies.

Materials and Methods

Study Area and Soil Sampling

The study was conducted in the Central Agro-Climatic Zone of Telangana, India, covering major cereal-growing districts including Khammam, Warangal, and Medak. The region experiences a semi-arid tropical climate with an average annual rainfall of approximately 996 mm, largely received during the southwest monsoon. Soils are predominantly Alfisols derived from granitic parent material. A total of 59 surface (0-15 cm) soil samples were collected from rice and maize cultivated fields following standard soil sampling procedures. Composite samples were prepared to ensure representativeness of each site.

Laboratory Analysis

Soil samples were air-dried, ground, and sieved (<2 mm) prior to analysis. Soil pH and electrical conductivity were assessed in a 1:2.5 soil-water solution utilizing a pH meter and conductivity meter, respectively [6] . Organic carbon was quantified by the Walkley and Black method [7] . Available nitrogen was estimated by the alkaline KMnO₄ method [8] . Available phosphorus was extracted by Olsen's method and quantified using the ascorbic acid reduction method at 660 nm [9,10] . Available potassium was extracted using neutral normal ammonium acetate and quantified with a flame photometer [6] . DTPA-extractable iron and zinc were quantified using atomic absorption spectrophotometry [11] .

Statistical Analysis

To evaluate variability, descriptive statistics such as range, mean, standard deviation (SD), and coefficient of variation (CV) were computed. Pearson's correlation coefficients were generated to examine correlations among soil properties. PCA was conducted on standardized data using the correlation matrix, and components with eigenvalues greater than one were retained. Variables with absolute loadings ≥0.50 were considered significant contributors. Statistical analyses were conducted using standard statistical R-software.

Results

The physicochemical properties and available nutrient status of Alfisols from the Central agro-climatic Telangana Zone (CTZ) are presented in Table 1. The soils were slightly acidic to moderately alkaline, with pH ranging from 6.65 to 7.78 and mean values close to neutral (7.19-7.23) Overall, the Alfisols of CTZ exhibited neutral reaction, low salinity, low to medium nitrogen and organic carbon, medium to high P and K, and largely adequate micronutrient availability.

Correlation Analysis

Correlation analysis revealed a significant positive relationship between organic carbon and available nitrogen (r = 0.419), emphasizing the role of soil organic matter as a primary reservoir and regulator of nitrogen availability (Fig. 1). This relationship has been widely reported in tropical agricultural soils.

Available phosphorus exhibited a significant negative correlation with iron (r = -0.278), indicating phosphorus fixation by iron oxides, a well-documented phenomenon in Alfisols. Electrical conductivity showed weak associations with micronutrients, suggesting localized effects of soluble salts on nutrient mobility. Overall, the observed correlations highlight the interconnected nature of soil fertility attributes and the limitations of isolated nutrient evaluation.

Principal Component Analysis

According to the scree plot, four principal components (PCs) were retained (Fig. 2). All these components exhibited eigenvalues greater than 1, with each explaining at minimum of 5% of the data variation, and together representing 63.9% of the total variation in soil attributes (Table 3). The Biplot shows the interrelationships among the soil attributes (Fig. 3). The pH, electrical conductivity, organic carbon, available nitrogen (N), P₂O₅ and K₂O were exhibited a positive correlation with one another, and negative correlation with properties in opposing directions. The OC and P₂O₅ aggregated together, indicating that they necessitate analogous management techniques. The first principal component (PC1), accounting for the largest share of variability, was strongly associated with organic carbon (0.81) and (0.84) available nitrogen (table 4), representing a soil organic fertility factor with eigenvalue of 2.41 and explained 26.8% of the observed variations in the soil properties (Table 3). This component underscores the central role of organic matter management in sustaining soil productivity.

Discussion

The soil organic carbon was typically low in the central zone districts of Telangana, attributed to diminished biomass production from crops and natural vegetation, alongside elevated turnover rates of organic material due to high soil temperatures and microfauna, particularly termite activity. The diminished content is intensified by overgrazing, bush burning, and the removal of soil cover, together with the accelerated breakdown and mineralization of organic compounds [12,13] .

The low concentrations of nitrogen, was directly due to the low organic C and its continuous mining without adequate replacement. Low available nitrogen status is the common observation in many soils and in many areas of the state as well as country because of the reason that were already enumerated for organic carbon content. The low available nitrogen status of the soil; as common phenomenon across the country is being reported over long time [14,15,16] . A analysis of 31 millet-producing soils in the Sahel zone revealed a strong link between organic carbon and total nitrogen, indicating that under the prevalent zero-input agro-pastoral systems, the nitrogen nutrition of crops significantly relies on the preservation of soil organic matter levels. This study clearly indicates that variations in geographical space, even within a single region, significantly affect the availability of soil nutrients due to substantial variances in soil physico-chemical parameters across the three locations. Consequently, the soils must be handled in a distinct manner. Ninety percent of these soils exhibited elevated levels of accessible phosphorus (p >59). Elevated phosphorus availability may result from a fixed phosphorus pool comprising inorganic phosphate compounds that exhibit low solubility and organic molecules that are resistant to microbial mineralization in soil. These findings corroborate the results documented by [18] in the soil of the Tonk district of Rajasthan and [19] . The potassium availability in Indian soils is reported to be medium to high in any instances [17,20,21] . Potassium rich minerals that varies in different types of soils and hence the present variation in potassium availability of surveyed samples expected [22,23] .

The management practices at central agro-climatic zone districts that could be relevant to planning site-specific crop production strategies for optimizing yield should focus on Organic carbon, Nitrogen, and available zinc. In this region, the PCA has also been used to screen soil properties for efficient soil management. The Principal Component Analysis (PCA) successfully reduced the dimensionality of the soil dataset, revealing that four primary factors explain nearly 64% of the total soil variability. This level of explanation is consistent with soil characterization studies in complex agroecosystems, where inherent pedogenic factors and anthropogenic management often overlap.

The Centrality of the Organic Fertility Factor (PC1) PC1, characterized by high loadings for Organic Carbon (0.81) and Available Nitrogen (0.84), serves as the "Organic Fertility Factor." The clustering of OC and P 2 O 5 in the biplot suggests that phosphorus availability in this region is tightly linked to organic matter mineralization rather than purely mineral dissolution. This mirrors the findings of [24] , who observed that in nutrient-limited soils, SOC acts as a primary reservoir for nitrogen and a mediator for phosphorus solubility, necessitating integrated nutrient management (INM) rather than isolated chemical fertilization.

Nutrient Fixation and Mineralogical Constraints (PC2 & PC3)

The inverse relationship between phosphorus (-0.77) and iron (0.79) in PC2 highlights a classic "P-Fe interaction." This interaction is indicative of phosphorus fixation, where iron oxides adsorb phosphate ions, rendering them unavailable for plant uptake. [25] noted that in soils with high iron activity, the management of pH and organic amendments is crucial to "mask" iron exchange sites and release fixed P. Furthermore, the mineralogical control over potassium (0.82) in PC3 suggests that K availability is likely governed by the parent material and clay mineralogy (e.g., illite or mica content). As [26] argue, potassium dynamics are often independent of organic matter cycles, requiring specific monitoring of exchangeable K pools to prevent "hidden hunger" in high-demand crops.

Salinity and Micronutrient Dynamics (PC4)

The association between EC (0.71) and Zinc (0.74) in PC4 points toward salinity-induced micronutrient variability. In semiarid regions, high electrical conductivity often leads to the formation of insoluble zinc complexes or competitive uptake inhibition. Research by [27] confirms that in saline-alkali environments, zinc solubility is significantly reduced, suggesting that farmers in areas with high PC4 scores may need to prioritize chelated zinc applications or foliar sprays to bypass soil-binding constraints.

Conclusion

This study demonstrates that the integration of descriptive statistics and multivariate analysis-specifically Principal Component Analysis (PCA)-offers a robust framework for decoding soil fertility in the Alfisols of Telangana's Central Agro-Climatic Zone. Our findings identify low organic carbondriven nitrogen deficiency, iron-mediated phosphorus fixation, and erratic zinc distribution as the primary constraints to cereal productivity. By distilling complex chemical interactions into four actionable thematic areas-organic restoration, fixation mitigation, mineral supplementation, and salinity balancingthis research provides the evidence base needed to transition from generic "blanket" applications to precise, site-specific nutrient management strategies.

References

1. Bhattacharyya R, Ghosh B, Mishra P, Mandal B, Rao C, Sarkar D, et al. Soil degradation in India: Challenges and potential solutions. Sustainability. 2015;7(4):3528-3570.
2. Cogle AL, Rao KPC, Yule DF, Smith GD, George PJ, Srinivasan ST, et al. Soil management and production of Alfisols in the semi-arid tropics. III. Long-term effects on water conservation and production. Aust J Soil Res. 1997;35(4):897-911.
3. Kuchimanchi BR, Bosch RR, De Boer IJM, Oosting SJ. Understanding farming systems and their economic performance in Telangana, India: Not all that glitters is gold. Curr Res Environ Sustain. 2022;4:100120.
4. Ellur R, Ankappa AM, Dharumarajan S, Puttavenkategowda T, Nanjundegowda TM, Sannegowda PS, et al. Soil quality assessment and its spatial variability in an intensively cultivated area in India. Land. 2024;13(7):970.
5. Vaibhav Bhagwan P, et al. Delineating soil fertility management zones using geostatistics and fuzzy clustering in semi-arid maize systems in India. Sci Rep. 2025.
6. Jackson ML. Soil chemical analysis. New Delhi: Prentice Hall of India Pvt. Ltd.; 1973.
7. Walkley A, Black IA. An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Sci. 1934;37(1):29-38.
8. Subbiah BV, Asija GL. A rapid procedure for the determination of available nitrogen in soils. Curr Sci. 1956;25(8):259-260.
9. Olsen SR, Cole CV, Watanabe FS, Dean LA. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. Washington DC: USDA Circular No. 939; 1954.
10. Watanabe FS, Olsen SR. Test of an ascorbic acid method for determining phosphorus in water and NaHCO3 extracts from soil. Soil Sci Soc Am J. 1965;29(6):677-678.
11. Lindsay WL, Norvell WA. Development of a DTPA soil test for zinc, iron, manganese, and copper. Soil Sci Soc Am J. 1978;42(3):421-428.
12. Ibrahim J, Aliyu J, Shobayo B. Characterization, classification and agricultural potentials of soils of Gabari district, Zaria, northern Guinea savanna zone. Biol Environ Sci J Trop. 2016;13:102-113.
13. Voncir N, Mustapha S, Amba AA, Kparmwang T. Inherent fertility status of Alfisols, Inceptisols and Entisols in the Gubi soil series, Bauchi, Bauchi State, Nigeria. J Appl Sci. 2006;6:2825-2828.
14. Dwivedi B, Tembhare BR, Gupta GP. Vertical distribution of available nutrients in Haplusterts and Haplustepts of Bheeta village, Jabalpur, Madhya Pradesh. JNKVV Res J. 1998;32:59-61.
15. Karthikeyan K, Prasad J. Soil fertility status of soybean (Glycine max L.) growing soils of Malwa Plateau, Madhya Pradesh. J Indian Soc Soil Sci. 2014;62(2):174-178.
16. Prasad M, Mahawer SK, Govindasamy P, Kumar S. Assessment of soil fertility attributes in selected districts of Bundelkhand region of Central India. Curr J Appl Sci Technol. 2020;39(48):326-334.
17. Manu A, Bationo A, Geiger SC. Fertility status of selected millet producing soils of West Africa with emphasis on phosphorus. Soil Sci. 1991;152:315-320.
18. Meena HB, Sharma RP, Rawat US. Status of macro and micronutrients in some soils of Tonk district of Rajasthan. J Indian Soc Soil Sci. 2006;54:508-512.
19. Bharteey PK, Singh YV, Sukirtee PS, Kumar M, Rai AK. Available macro nutrient status and their relationship with soil physico-chemical properties of Mirzapur district of Uttar Pradesh, India. Int J Curr Microbiol Appl Sci. 2017;6(7):2829-2837.
20. Ghosh AB, Hasan R. Available potassium status of Indian soils. J Indian Soc Soil Sci. 1976;10:1-5.
21. Subbarao A, Srinivasa Rao C. Potassium status and crop response to K in different agro-ecological regions of India. IPI Res Top. 1996;20:1-57.
22. Dwivedi B, Tembhare BR, Gupta GP. Vertical distribution of available nutrients in Haplusterts and Haplustepts of Bheeta village, Jabalpur, Madhya Pradesh. JNKVV Res J. 1998;32:59-61.
23. Gurav PP, Ray SK, Choudhari PL, Shirale AO, Meena BP, Biswas AK, et al. Potassium in shrink-swell soils of India. Curr Sci. 2019;117(4):587-596.
24. Zheng H, Chen Z, Wang Z. Synergistic effects of organic carbon on nitrogen and phosphorus availability in agricultural soils. 2021.
25. Fink JR, Inda AV, Bayer C, Torrent J, Barrón V. Iron oxides and phosphorus adsorption in southern Brazilian soils. 2016.
26. Sardans J, Peñuelas J. Potassium control of plant functions: Ecological and agricultural implications. 2021.
27. Hafeez B, Khanif YM, Saleem M. Role of zinc in plant nutrition-A review. 2013.