Variability in soil physico-chemical properties and leaf macronutrient composition of groundnut in semi-arid soils of Tirupati district, Andhra Pradesh

Introduction

Groundnut (Arachis hypogaea L.) is one of the important oil seed crops cultivated in tropical and semi-arid regions of India. It plays a significant role in edible oil production and contributes considerably to agricultural economy. The productivity of groundnut is greatly influenced by soil fertility status and balance in water and management. Macronutrients are essential for proper plant growth, nodulation, photosynthesis, energy transfer and yield formation. Deficiency or imbalance of these nutrients adversely effects crop growth, nutrient uptake and productivity (Kumar et al., 2023) [13] . The availability and uptake of nutrients by crops are largely controlled by soil physicochemical properties. These properties influence nutrient solubility, mobility, retention and transformation in soils. Variability in soil properties under semi-arid regions often leads to differences in nutrient dynamics and crop response (Gudla et al., 2023) [8] . Leaf nutrient analysis is considered as effective diagnostic tool for evaluating the nutritional status of crops because it reflects the actual nutrient uptake by plants. Combined assessment of soil properties and plant nutrient composition provides better understanding of nutrient availability and nutrient use efficiency under varying soil conditions. Such studies are useful for identifying nutrient related constraints on developing suitable nutrient management practices for sustaining crop productivity and soil health (Rajesh et al., 2023) [18] . Soil organic carbon dynamics and nutrient availability are also greatly influenced by management practices and variability in semi-arid soils (Gorooei et al., 2023) [7] . The soils of semi-arid regions often exhibit considerable heterogeneity in their physico-chemical characteristics due to variations in parent material, topography and pedogenic processes. Such variability influences nutrient retention, transformation and crop uptake patterns (Baradwal et al., 2023) [2] . Hence, the present study was undertaken to evaluate leaf macronutrient composition and its relationship with soil physico-chemical properties for developing site-specific nutrient management strategies in groundnut growing soils of Puttur division in Tirupati district, Andhra Pradesh.

Materials and Methods

Study area description

The present investigation was conducted in the groundnut growing soils of Puttur division situated in Tirupati district of Andhra Pradesh. The Puttur division is located in the southern part of the district, lying between the latitudes of 13°.24' and 13°.58' N and longitudes of 79°.23' and 79°.59' E. The climate of the study area is characterized as semi-arid and monsoonic, with three distinct seasons: summer, winter and rainy seasons. The mean annual air temperature for the area is 27.68°C with the yearly rainfall averaging around 1092 mm. The Puttur division consists of four mandals: Puttur, Narayanavanam, Vadamalpeta and Ramachandrapuram mandal. Granite-gneiss is the dominant parent material in the study area. Groundnut is the most prevalent crop in the study area together with other significant crops like rice, sugarcane, mango, coconut, banana, cowpea, niger and chilli. The site characteristics of the surface soils collected are presented in Table 1.

Soil sampling and analysis

Twenty surface soil samples were collected in groundnut growing soils of Puttur division in Tirupati district, Andhra Pradesh based on the soil variability and land use pattern. The soil samples were collected, processed and analyzed for physicochemical properties following standard procedures. Soil pH (1: 2.5 soil:water) and 1 N KCl suspensions were quantified potentiometrically, alongside EC (1: 2.5 soil:water) via conductivity meter (Jackson, 1973) [9] . Organic carbon content was analysed by the Walkley and Black's wet oxidation method (Jackson, 1973) [9] . Free calcium carbonate in the soil was estimated by treating the sample with a known volume of standard HCl, followed by back titration of the excess acid with standard alkali using bromothymol blue as an indicator (Piper, 1966) [17] . CEC (cmol (p + ) kg -1 soil) was assessed by NH 4 OAc (pH 7.0) displacement following NaOAc (pH 8.2) saturation and ethanol leaching and sodium in the extract was measured by flame photometer (Bower et al., 1952) [4] .

Collection, processing and analysis of plant samples

Index leaf samples (Recently matured leaflets) collected from the plants growing in and around each profile site. The collected leaf samples were washed thoroughly with distilled water and extra moisture was wiped out and dried in shade. Finally, the samples were dried in hot air oven at 70°C, powdered and stored for analysis. The powdered samples were analysed for macronutrients using standard analytical procedures. Nitrogen content was determined by microkjeldahl method (Bremner, 1965) [5] , phosphorus was estimated by vanadomolybdo phosphoric yellow colour method (Jackson, 1973) [9] , potassium by flame photometer (Muhr et al., 1963) [16] and sulphur by turbidity method (Cottenie et al., 1979) [6] .

Ratings for nutrient contents in leaf samples

The nutrient contents in leaf samples were classified as severely deficient, deficient, marginally adequate and adequate categorized as per the limits suggested by Bell (1990) [3] (Table 2). [22] . Electrical conductivity of the soil water extract was ranged from 0.13 to 0.53 dS m -1 , indicating the non-saline nature of the soils.

The overall low electrical conductivity (EC) values reflect favourable drainage conditions and effective leaching of soluble salts under groundnut cultivation, which facilitates the downward movement and removal of released bases through percolating water (Jayasree et al., 2022) [11] . As the threshold level of soluble salts for groundnut is less than 2 dS m -1 , all the studied soils are suitable for groundnut growth with respect to salinity. Organic carbon concentrations varied greatly among the surface soils, ranging between 0.34 and 0.65 per cent and exhibiting low to medium organic carbon levels. Relatively higher soil organic carbon in surface soils are primarily due to greater inputs from crop residues and farmyard manure than in sub-surface soils. Generally, soil organic carbon levels are low because of the rapid decomposition of organic matter and the limited areas of vegetative cover usually typical of tropical climates restrict build-up of soil organic carbon (Shahi et al., 2021) [20] . [21] .

Leaf macronutrient composition

The macronutrient composition of index leaves of groundnut collected from the study area is present in Table 4.

Nitrogen: Nitrogen content in index leaf samples of groundnut ranged from 2.27 to 3.39 per cent indicating severely deficient to deficient in the study area. The highest leaf nitrogen content of 3.39 per cent was recorded in groundnut crop grown in Taduku village, while the lowest nitrogen content of 2.27 per cent was recorded in Seetharamapuram village. The deficient leaf nitrogen status may be attributed to low organic carbon content, poor mineralization of organic matter under semi-arid conditions and coarse textured soils with low nitrogen retention capacity, which favoured nitrogen losses through leaching and volatilization. In addition, continuous cultivation and insufficient application of nitrogenous fertilizers may have further reduced nitrogen availability and uptake by the plants.

Similar observations regarding the influence of soil properties on nitrogen availability and nutrient uptake were reported by Rathore et al. (2021) [19] and Balagangathar et al. (2024) [1] .

Phosphorus: Phosphorus concentration in index leaf samples of groundnut was varied from 0.131 to 0.266 per cent indicating severely deficient to marginally adequate in the study area. The highest phosphorus content was recorded in Veluthurukandriga village, while the lowest was observed in Anupalli village. The deficient phosphorus status in leaf samples may be attributed to phosphorus fixation under alkaline soil conditions and the presence of free calcium carbonate, which reduced phosphorus solubility and availability to plants. Further, low organic matter content and limited phosphorus mobility in semi-arid soils might have restricted phosphorus diffusion towards plant roots, thereby reducing uptake. The comparatively higher leaf phosphorus concentration observed in some locations may be due to relatively favourable soil reaction and better phosphorus availability in the root zone, resulting in enhanced absorption by plants. Similar observations on phosphorus nutrition and nutrient uptake in groundnut were reported by Joshi et al. (2024) [12] . Potassium: Potassium concentration in index leaf samples of groundnut was ranged from 1.82 to 2.60 per cent indicating adequate level in the study area. The highest potassium content was observed in Kammapalli village, whereas the lowest value was recorded in Anupalli village. Higher leaf potassium concentration may be associated with greater potassium retention capacity of finer soil fractions and higher cation exchange capacity, which ensured sustained potassium availability to plants. Lower leaf potassium concentration may be due to reduced nutrient holding capacity and possible leaching losses, resulting in lower potassium availability and uptake by plants. Similar findings regarding the influence of soil properties on nutrient uptake and soil fertility in groundnut were reported by Jain et al. (2021) [10] . [14] and Maindar et al. (2024) [15] . Overall, the variability observed in leaf macronutrient composition indicated that soil physico-chemical properties such as pH, organic carbon and cation exchange capacity played an important role in nutrient availability and uptake in groundnut growing soils of Puttur division. The results emphasized the importance of site-specific nutrient management for sustaining soil fertility and crop productivity in the region.

Conclusion

The representative surface soils of Puttur division exhibited considerable variation in physico-chemical properties and leaf macronutrient composition of groundnut. Soil reaction ranged from slightly acidic to moderately alkaline, while electrical conductivity indicated the non-saline nature of the soils. Organic carbon status ranged from low to medium in most locations, whereas higher cation exchange capacity was associated with finer fractions. Leaf nitrogen, phosphorus, potassium and sulphur concentrations also varied across the study sites due to differences in nutrient availability and related physico-chemical characteristics. The findings demonstrated the influence of soil physico-chemical properties on nutrient dynamics and nutrient uptake, indicting the need for site-specific nutrient management strategies for sustainable groundnut production in Puttur division of Tirupati district in Andhra Pradesh.

Acknowledgement

AcknowledgementThe authors acknowledge the Acharya N.G. Agricultural University, Tirupati, Andhra Pradesh, India, for providing library and web source facilities for writing the manuscript.Funding: This research received no external funding.

References

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