Assessment of soil fertility status and nutrient relationships in agricultural soils of Sangli District, Maharashtra, India

Introduction

Soil health is essential for agricultural productivity, as it supports nutrient cycling and carbon storage, both of which are crucial for stable crop yields (Shahane & Shivay, 2021) [20] . In India, the drive to increase food production has led to intensive farming and the overuse of chemical fertilizers, which often harms soil fertility and reduces how efficiently crops use nutrients (Bhattacharyya et al., 2015) [4] . For regions like Sangli in Maharashtra, with varied cropping patterns and climates, understanding how nutrients are distributed across the landscape is critical for developing site-specific nutrient management (Akhil et al., 2025) [1] However, detailed, local data on the current soil fertility status and the complex relationships between nutrients in Sangli's agricultural lands remain limited, complicating efforts to create effective agricultural policies (Hadole et al., 2024; Sharma et al., 2022) [9,21] . This gap in localized information limits our ability to optimize fertilizer use and prevent soil degradation, which is a growing concern. Therefore, this study aims to evaluate the soil fertility status and analyse the interactions between different soil parameters in Sangli. By providing these essential insights, the research will help support sustainable land management practices, enhance regional agricultural productivity, and guide future efforts to maintain long term soil health.

Materials and method

The present study was conducted for Sangli district of Maharashtra, India. Sangli district is situated in the southern part of Maharashtra and lies between 16°43′ to 17°38′ north latitude and 73°41′ to 75°41′ east longitude.

It is characterized by a semi-arid tropical climate with predominantly black soils derived from basaltic parent material. Agriculture is the major land use in the district, with sugarcane, soybean, sorghum, wheat, and horticultural crops being commonly cultivated. The study was based on soil fertility data obtained from the Soil Bank, Department of Soil Science and Agricultural Chemistry, Mahatma Phule Krishi Vidyapeeth (MPKV), Rahuri, Maharashtra. The database comprised geo-referenced total 341 surface soil samples (0-20 cm depth) collected from different locations across Sangli district. The dataset included soil reaction (pH), electrical conductivity (EC), organic carbon (OC), available nitrogen (N), available phosphorus (P), and available potassium (K). Soil reaction (pH) and electrical conductivity (EC) were determined in a 1:2.5 soilwater suspension following the procedure of Jackson (1973) [11] . Soil organic carbon was estimated by the wet oxidation method of Nelson and Sommers (1982) [15] . Available nitrogen was determined by the alkaline permanganate method (Subbiah and Asija, 1956) [22] . Available phosphorus was estimated by the Olsen method (Watanabe and Olsen, 1965) [24] , while available potassium was determined by flame photometry after extraction with neutral normal ammonium acetate (Jackson, 1973) [11] . The fertility status of soil organic carbon (OC), available nitrogen (N), available phosphorus (P), and available potassium (K) was classified into very low, low, moderate, moderately high, high, and very high categories according to the criteria suggested by Patil and Mali (1999) [19] . Soil pH and electrical conductivity (EC) were classified following the guidelines of Bangar and Zende (1978) [2] . Pearson's correlation analysis was performed to examine the relationships among soil properties, namely pH, EC, organic carbon, available nitrogen, available phosphorus, and available potassium. The correlation matrix was generated using Python software to determine the strength and direction of association among the soil fertility parameters. The descriptive statistics of soil properties in Sangli district are presented in table 1. The mean soil pH was 7.96, indicating that the soils were predominantly neutral to moderately alkaline. The mean EC was 0.34 dS m⁻¹, suggesting that most soils were nonsaline. The average SOC content was 0.62%, which indicated a moderate level of soil organic carbon. The mean available N, P, and K contents were 207.26, 15.88, and 439.94 kg ha⁻¹, respectively. The results showed that available nitrogen and phosphorus were generally low, whereas potassium was comparatively high. The coefficient of variation was lowest for pH (4.85%), indicating relatively low variability among the samples. The EC, available P, and available K showed higher variability, reflecting differences in soil properties and nutrient status across the study area. The distribution of soil pH classes revealed that the soils of Sangli district were predominantly alkaline in nature (Table 2). The samples (56.01%) were classified as moderately alkaline (pH 8.1-9.0), followed by 33.14% under the slightly alkaline category (pH 7.1-8.0). Small proportion of soils were moderately acidic (5.28%), slightly acidic (4.11%), and neutral (1.47%). No samples belonged to the extremely acidic or strongly alkaline categories. The predominance of alkaline soils may be attributed to the semi-arid climate, limited leaching due to low rainfall, and the accumulation of exchangeable basic cations such as calcium and magnesium in the soil (Weil and Brady 2017) [25] . These results indicate that soil reaction in the district is generally favourable for crop production; however, alkaline conditions may reduce the availability of phosphorus and micronutrients such as iron, zinc, and manganese (Havlin, 2014) [10] . The predominance of alkaline soils observed in the present study is consistent with earlier reports from Sangli district. Patil et al.

Results and discussion

Descriptive statistics of soil properties

Soil properties distribution status 3.2.1 Soil pH

(2017) [18] recorded slightly to moderately alkaline soils in Kadegaon tehsil, with pH ranging from 7.09 to 8.21. Similar alkaline soil conditions have also been reported in other parts of Maharashtra (Hadole et al., 2024; Jagtap et al., 2018) [9,13] . The distribution of soil electrical conductivity (EC) classes in Sangli district is presented in table 3. The majority of soil samples (90.62%) were classified as normal (0-1 dS m⁻¹), indicating that salinity is generally not a major constraint in the district. However, 7.62% of the samples observed under the poor seed emergence category (1-2 dS m⁻¹), while 1.76% were classified as harmful to some crops (2-3 dS m⁻¹). These findings indicate that most agricultural soils are suitable for crop production, although localized salinity problems exist in a few areas, which may affect seed germination and crop growth if not managed properly. The occurrence of localized salinity in the area may be attributed to limited rainfall, the buildup of soluble salts in the soil profile, low-lying topographic positions that favour salt accumulation, and the use of irrigation water containing elevated salt concentrations (Gedam et al., 2021) [5] .

Electrical conductivity

The presence of a few samples with elevated EC values suggests minor salinity variations within the district. Comparable EC ranges have been reported from Satara (Hadole et al., 2024) [9] , Kolhapur (Kumar et al., 2020) [14] and other parts of western Maharashtra (Ghodke et al., 2016) [6] , where most soils were non-saline but occasional samples showed relatively higher EC values.

Soil organic carbon

The distribution of soil organic carbon (SOC) classes is presented in table 4 [9] and Surwase et al. (2024) [23] , indicating variability in soil organic carbon across agricultural soils of the region.

Available Nitrogen (N)

Available nitrogen status was predominantly low, with 95.60% of soil samples falling under the low category (Table 4 and Figure 1). Only 3.52% of the samples were classified as moderate and 0.88% as very low, while no samples were recorded in the moderately high, high, or very high categories. The widespread nitrogen deficiency may be due to low organic matter mineralization and continuous nutrient removal by crops without adequate nitrogen replenishment (Behera et al., 2025) [3] . Similar low nitrogen status was reported by Patil et al. (2017) [18] in Kadegaon tehsil of Sangli district, where continuous cultivation and low organic matter content contributed to nitrogen deficiency in soils. Also, Ghodke et al. (2016) [6] reported that nearly 70 per cent of soils from western Maharashtra were low in available nitrogen.

Available Phosphorus (P)

The distribution of available phosphorus showed that 30.21% of the samples were in the low category, followed by moderate (21.41%), very low (19.94%), and moderately high (19.35%) classes (Table 4 and Figure 1). High and very high phosphorus levels were observed in only 8.80% and 0.29% of the samples, respectively. These results indicate that phosphorus availability is generally low to moderate in the soils of Sangli district, which may limit crop productivity in some areas. The low to moderate phosphorus status may be related to fixation of phosphorus in alkaline and calcareous soils, which reduces its availability to plants (Omar et al., 2024) [16] . Similar findings were reported by Patil et al. (2017) [18] in Sangli district, where available phosphorus was predominantly low to medium. Likewise, Hadole et al. (2024) [9] observed low to medium phosphorus status and attributed it to alkaline soil conditions and phosphorus fixation. Ghodke et al. (2016) [6] also reported that soil pH and calcium carbonate content influenced phosphorus availability, resulting in low to moderate phosphorus levels in the soils of western Maharashtra.

Available Potassium (K)

Available potassium content was generally high across the district (Table 4 and Figure 1). The majority of the soil samples (64.52%) were classified in the very high category, followed by moderately high (12.32%), moderate (9.09%), and high (8.80%) classes. Only 5.28% of the samples were in the low category, and no samples were classified as very low. The high potassium status may be attributed to the presence of potassium-rich parent materials and the release of potassium through weathering of soil minerals (Gurav et al., 2018) [7] . The high potassium status recorded in the present study is consistent with earlier findings from Sangli district and other parts of Maharashtra. Similar moderate to high available potassium levels were reported in the soils of Kadegaon tehsil, Sangli district (Patil et al., 2017) [18] . Comparable observations were also reported from different regions of Maharashtra (Chaudhari et al., 2019; Jagtap et al., 2019; Kumar et al., 2020) [12, 14] .

Correlation among soil properties

The Pearson correlation matrix among soil properties is presented in Figure 2. Soil pH exhibited significant negative correlations with EC (r = -0.12), SOC (r = -0.30), available N (r = -0.29), and available P (r = -0.24). These relationships indicate that increasing soil alkalinity may reduce the availability and accumulation of certain nutrients. However, pH showed a weak positive correlation with available K (r = 0.16), suggesting that potassium availability was less affected by soil reaction. Soil organic carbon (SOC) was positively correlated with available N (r = 0.38), P (r = 0.30), and K (r = 0.15). The strongest correlation was observed between SOC and N, highlighting the role of soil organic matter as a major source of nitrogen through mineralization processes. The positive association between SOC and phosphorus further suggests the contribution of organic matter to nutrient retention and availability. Available nitrogen showed significant positive correlations with EC (r = 0.34) and P (r = 0.33), indicating that soils with higher nutrient status tended to contain greater amounts of both nitrogen and phosphorus. Similarly, available phosphorus was positively correlated with EC (r = 0.23) and K (r = 0.18). Available potassium exhibited weak positive correlations with most soil properties, reflecting its generally high abundance in the study area. [14] observed a positive relationship between soil organic carbon and available nitrogen, indicating the role of organic matter in nutrient mineralization. Pandey et al. (2021) [17] reported significant negative correlations of soil pH with nutrient availability and positive associations between organic carbon and major nutrients. Likewise, Gurumurthy et al. (2022) [8] found that available phosphorus was negatively correlated with soil pH, while soil organic carbon showed positive relationships with available nutrients.

Conclusion

The soils of Sangli district were predominantly moderately alkaline and non-saline, indicating generally favourable conditions for agricultural production. However, a small proportion of soils exhibited elevated electrical conductivity, suggesting localized salinity issues that may affect crop growth in certain areas. Soil organic carbon status was mostly moderate to high, reflecting a relatively good organic matter reserve. Available nitrogen was predominantly low, identifying nitrogen deficiency as the major soil fertility constraint in the district. Available phosphorus was largely in the low to moderate range, whereas available potassium was sufficient to very high in most soils. Correlation analysis revealed positive relationships between soil organic carbon and nutrient availability, highlighting the importance of organic matter in maintaining soil fertility. In contrast, higher soil pH was associated with reduced availability of nitrogen and phosphorus. The results indicate that improving nitrogen nutrition, maintaining soil organic matter, managing phosphorus efficiently, and addressing localized salinity where present are important for sustaining soil fertility and enhancing crop productivity in Sangli district.

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