Soil macronutrient status under different land use systems in Mahabubnagar district, Telangana

Introduction

The productivity and long-term sustainability of cropping systems largely depend on soil fertility, which is strongly influenced by land use and management practices. Changes in land use, such as conversion of natural vegetation to cultivated land, intensive cropping, residue removal and continuous tillage, can significantly modify soil physical, chemical and biological properties, resulting in variations in soil nutrient availability and overall soil quality (Lal, 2004) [8] . Nitrogen (N), phosphorus (P) and potassium (K) are the primary macronutrients required for optimum crop growth and development. Nitrogen is an essential constituent of amino acids, proteins, nucleic acids and chlorophyll, and its availability is governed by biological processes such as mineralisation, immobilisation, nitrification and denitrification (Brady and Weil, 2017; Robertson, G.P. and Groffman, P.M., 2015) [1,16] . Phosphorus plays a crucial role in energy transfer, root growth and reproductive development, but its availability is often limited because of fixation reactions in soil (Hinsinger, 2001) [14] . Potassium is involved in enzyme activation, photosynthesis, osmotic regulation and stress tolerance, and its availability gradually declines under intensive cultivation due to continuous nutrient removal and inadequate replenishment (Zörb et al., 2014; Das et al., 2019) [23,2] . Differences in vegetation cover and management practices among land use systems substantially influence soil macronutrient status. Forest ecosystems generally retain higher nutrient availability, while cultivated lands are more prone to nutrient depletion due to continuous cropping and biomass removal (Liu et al., 2010) [10] . Similar observations have been reported from Telangana, where land use systems significantly influenced the availability of nitrogen, phosphorus and potassium, emphasizing the need for location-specific nutrient management strategies (Poojitha et al., 2024; Kiran Reddy and Goverdhan, 2012) [14,17] . The present investigation was undertaken to evaluate the influence of different land use systems on the soil macronutrient status, with particular emphasis on the availability of nitrogen, phosphorus and potassium, in the soils of Mahabubnagar district, Telangana. The findings of this study will contribute to a better understanding of nutrient dynamics and provide scientific information for developing land use-specific nutrient management strategies to sustain soil fertility and agricultural productivity.

Materials and Methods

The study was conducted during 2025 under 7 major land use systems (i.e., rice-rice, maize-groundnut, groundnut-fallow, cotton-fallow, mango, fodder and forest, in Mahabubnagar district, Telangana which lies between 15"55′ and 17"29′ N latitude and 77"15′-79"15′ E longitude and experiences a semiarid climate with an average annual rainfall of 729 mm. The mean maximum and minimum temperatures are 40.9°C and 25.0°C, respectively, while the annual maximum and minimum relative humidity ranges from 75-82% and 45-47%. A total of 140 soil samples were collected from 70 representative sites (10 from each land use system) at two depths (0-15 and 15-30 cm). The GPS coordinates of each sampling location were recorded. Soil samples were shade-dried, gently crushed, passed through a 2-mm sieve and stored for laboratory analysis. Available nitrogen, phosphorus and potassium were determined using standard analytical procedures. Available nitrogen was estimated by the alkaline potassium permanganate method (Subbiah and Asija, 1956) [21] . Available phosphorus was extracted with 0.5 M sodium bicarbonate (Olsen's reagent) following Olsen et al. (1954) [13] , and its concentration was determined by the ascorbic acid blue colour method using a spectrophotometer at 660 nm. Available potassium was extracted with 1 N neutral ammonium acetate and measured using a flame photometer as described by Jackson (1973) [5] . The nutrient contents were expressed in kg ha⁻¹. The data were analysed using two-way analysis of variance (ANOVA) following Snedecor and Cochran (1967) [20] at the 5% level of significance, considering land use systems and soil depths as the main factors along with their interaction.

Results and Discussion

Available nitrogen

Available nitrogen under different land use systems ranged from 212.4 to 312.6 kg ha⁻¹ at 0-15 cm and 180.3 to 288.5 kg ha⁻¹ at 15-30 cm depth (Table 1 and Figure 1). The highest mean available nitrogen (300.5 kg ha⁻¹) was recorded under the forest land use system, whereas the lowest value (196.3 kg ha⁻¹) was observed under cotton-fallow. Available nitrogen decreased with increasing soil depth across all land use systems, and the interaction between land use systems and soil depths was nonsignificant. Across all land use systems, available nitrogen decreased with increasing soil depth, likely due to the higher organic matter content, greater root activity, and enhanced microbial processes in the surface soil compared to the subsoil (Ajeet Kumar et al., 2025; Maqbool et al., 2017) [7,11] . The higher nitrogen status in forest soils may be attributed to continuous litter deposition, greater organic matter accumulation and enhanced microbial mineralisation, whereas intensive cultivation, repeated crop removal and lower organic residue inputs under cultivated lands contributed to nitrogen depletion (Liu et al., 2010) [10] . Similar trends of higher available nitrogen under forest and perennial vegetation, together with a decline in nitrogen with soil depth, have been reported in Telangana by Ramprasad et al. (2014) [15] , Gade KR et al. (2021) [18] and Devi Shravani et al. (2025) [19] . These findings indicate that land use systems play a significant role in regulating soil nitrogen dynamics and maintaining soil fertility.

Available phosphorus

Available phosphorus under different land use systems ranged from 35.93 to 54.05 kg ha⁻¹ at 0-15 cm and 32.65 to 51.6 kg ha⁻¹ at 15-30 cm depth (Table 2 and Figure 2). The highest mean available phosphorus (52.83 kg ha⁻¹) was recorded under the forest land use system, whereas the lowest value (34.29 kg ha⁻¹) was observed under cotton-fallow. Available phosphorus declined with increasing soil depth and a significant interaction between land use systems and soil depths was observed. Hinsinger, P. (2001) [4] observed that available phosphorus was concentrated in surface soils because plant residues and microbial activity predominantly occur in the upper soil horizons. Negassa and Leinweber (2009) [12] concluded that long-term cultivation without adequate phosphorus replenishment gradually depletes available phosphorus through continuous crop removal and transformation into less available phosphorus fractions. Likewise, under Telangana conditions, Poojitha et al. (2024) [14] reported that contrasting land use systems significantly altered available phosphorus status, with natural vegetation maintaining comparatively higher phosphorus than cultivated fields. Similarly, Reddy et al. (2021) [6] observed a decline in available phosphorus with increasing soil depth in Telangana soils, attributing it to phosphorus fixation and lower organic matter in subsurface horizons. These findings confirm that land use and soil depth jointly influence phosphorus availability and overall soil fertility.

Available potassium

Available potassium content under different land use systems ranged from 262.05 to 360.68 kg ha⁻¹ at 0-15 cm and 242.87 to 341.08 kg ha⁻¹ at 15-30 cm depth (Table 3 and Figure 3). The highest mean available potassium (350.88 kg ha⁻¹) was recorded under the forest land use system, whereas the lowest value (252.46 kg ha⁻¹) was observed under the rice-rice system. Available potassium decreased with increasing soil depth across all land use systems, while the interaction between land use systems and soil depth was non-significant. Wakeel and Ishfaq (2022) [22] reported that continuous return of plant residues enhances potassium recycling and helps maintain available potassium under perennial vegetation and minimally disturbed ecosystems. In contrast, intensive cultivation and continuous nutrient removal under agricultural systems may have reduced the available potassium content due to inadequate replenishment (Das et al., 2022) [3] . Similar findings were reported by Poojitha et al. (2024) in Telangana, where forest soils maintained higher available potassium than cultivated lands. Lalitha and Dhakshinamoorthy (2019) [9] further explained that higher potassium availability in surface soils is maintained through the equilibrium among different soil potassium fractions and continuous residue recycling. These findings demonstrate that both land use and soil depth play an important role in governing potassium availability and overall soil fertility.

Conclusion

The present study confirmed that land use systems are a major determinant of soil macronutrient status in Mahabubnagar district, Telangana. Forest ecosystems maintained superior nitrogen, phosphorus and potassium availability, whereas cultivated lands showed comparatively lower nutrient status, with all macronutrients decreasing with soil depth. These findings underscore the need for land use-specific nutrient management and conservation practices to sustain soil health and agricultural productivity.

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