Shifting soil dynamics: Unveiling physicochemical changes in Punjab region

Introduction

India encompasses a total geographic area of 328 million hectares, accounting for 2.5% of the world's total land area. Punjab possesses a varied topography spanning an area of 50,362 km 2 located in the north-western region of the country. It accounts for 1.54% of India's overall land area. Punjab is widely recognized as one of the most agriculturally productive states in India. Approximately 84% of the state's land is used for agriculture, whereas only 6% is shaded by forests. Through forest restoration and agroforestry practices, Punjab has managed to increase the amount of forest land from 3.72% in 1966 to 6.07% in 2012. Punjab is a major producer of rice and wheat, accounting for approximately 20-30% and 10 -1 2% of the total production, respectively. Additionally, Punjab contributes around 9 -1 1% of cotton production, 20-30% of honey production, 45-50% of mushroom production, and 9 -1 0% of milk production. Punjab has been the largest producer of food grain from 1960-61 to 2007-08, with production increasing from 3.16 to 26 million tons. It has maintained its status as the top producer till the year mentioned (Maninder et al., 2020) [27] . The predominant agricultural system in Punjab is ricewheat, which covers 60 percent of the total farmed land. The average productivity of rice (unhusked paddy) is 6.0 tons per hectare, while wheat has an average output of 4.7 tons per hectare. Punjab's cropping intensity stands at 190.3 percent. The implementation of the green revolution in Punjab, India involved the application of significant amounts of inorganic fertilizer. This led to alterations in the physiochemical characteristics of the soil, negatively impacting its health. Consequently, this may contribute to a future increase in nutrient deficiencies in Indian agriculture, exacerbating the crisis of nutrient scarcity. The Punjab region is primarily partitioned into three distinct regions known as Doaba, Majha, and Malwa.

Majha Region

The Majha division of Punjab is located in the northwestern part of Punjab, covering an area of around 5182 square kilometers. The distance of 7 square kilometers encompasses the region located between the Beas and Ravi rivers. The northern section of Sutlej, beyond the point where Beas and Sutlej rivers meet in Tarn Taran district, and stretching up to the Ravi River, is also included in the Majha region (Singh et al., 2021) [45] . The term "Majha" signifies being positioned in the middle or at the center.

The geographical location of this area lies in the central part of the traditional Punjab province, which is why it is referred to as Majha. The 4 districts of Punjab that are included in this region are Amritsar, Gurdaspur, Pathankot, and Tarn Taran (Kumar, 2021) [22] .

Malwa region

The territory on the opposite side of the Sutlej River in the Punjab region is known as Malwa. It encompasses an approximate area of 48780 square kilometers in Punjab and consists of two subsoil orders, ustic and udic (Bast and Balasubrahmanyan 2021) [2] . This region encompasses around 60-70% of the total land area of Punjab state. The region includes fifteen districts of Punjab: Barnala, Bathinda, Fatehgarh Sahib, Faridkot, Fazilka, Firozpur, Ludhiana, Mansa, Moga, Mohali, Muktsar, Patiala, Ropar, and Sangrur (Central Ground Water Board Punjab, 2016) [8] . The Malwa region is classified as having a semi-arid climate. The average temperature fluctuates between 5 °C during the winter months (December-January) and 45 °C during the summer months (May-June). The region experiences an average annual precipitation of 600 mm. However, the majority of this rainfall, around 70%, is concentrated between the months of July and September, mostly due to the influence of the southwest monsoon season (Meena et al., 2024) [29] .

Fig 1: Malwa region

Soil of Punjab

The soil in Punjab is classified as three different moisture regimes: ustic zone, udic zone, and Aridic zone.

Ustic zone

Encompasses a significant portion of the Doaba region as well as most of the Majha and Malwa regions. The soil orders present in this region are Entisols, Inceptisols, Entisols-Inceptisols, and Inceptisols-Alfisols (Sagar, 2017) [38] . Ustic zone soil has developed in the central Punjab region, which experiences semiarid and moderately hot climatic conditions. These circumstances are different from the aridic zone soils found in the south-western part of the region (Sharma et al., 2005) [41] .

Udic zone

Udic zone is in the northeastern part of Punjab and encompasses the district of Pathankot. The soil order consists of Entisols, Inceptisols, and Inceptisols of the udic zone, as described by Kumar et al. in 2008 [23] . The topographic area of this zone consists of hills, a piedmont plain, and a flood plain, with a composition of fertile sand and silt loam. The soil quality is likewise devoid of macronutrients. Areas with adequate irrigation but limited water supply may experience issues with soil alkalinity or salinity. Additionally, arid regions may face significant erosion concerns (Chopra 1990) [9] .

Aridic zone

Aridic zone is in the southwestern part of Punjab and includes four districts: Fazilka, Muktsar, and Bhatinda in the Malwa region. The majority of this area has soil types classified as Entisols, Aridisols, Entisols-Inceptisols, and Entisols-Aridisols. Some areas in this region are currently covered by a layer of wind-blown sand. This area is characterized by a prevailing dry and hot environment. The soils experience prolonged periods of aridity during the majority of the year. The surface of the soil consists of light-colored sandy loam to loam soils with a pH ranging from 8.0 to 8.3. Lime nodules are present in the subsurface horizon of these soils. An ochric epipedon is a layer of soil that is found within one meter of the surface and is situated above a cambic and/or calcic horizon. Dry circumstances greatly increase the susceptibility of soil to air erosion, and this type of soil is deficient in macronutrients (Singh et al., 2016) [47] .

Physical properties of soil Soil texture

Soil texture is a significant factor in determining the composition percentage of soil. The composition of sand, silt, and clay, which is immutable, may be quantified both in the field and in a laboratory setting. Soil texture has a significant impact on soil quality, particularly in terms of aeration, root penetration, and the uptake of soil nutrients. Soil texture can be accurately determined by measuring its electrical conductivity. [20] , Raya et al., (2004) [36] , Sharma et al., (2017) [42] , Surya et al., (2019) [50] , Bhatt et al., (2020) [5] . The Majha region soil texture in the districts of Amritsar, Gurdaspur, and Tarn Taran has been classified as loamy to sandy loam by researchers Singh et al., (2020) [48] , Elbaalawy et al., (2006) [11] , and Bhatt and Singh (2021) [3] accordingly. The present investigation in the Malwa region found that much of the area has soil texture ranging from sandy clay loam to sandy loam. The southern half of the Malwa region, including Barnala, Bhatinda, and Ludhiana districts, has identified a soil texture that is sandy clay loam. (Graham, 2006) [13] .

The pH of soil has a substantial impact on the availability of nutrients, the accessibility of trace elements, the biochemical processes, and the microbial activity in the soil, all of which affect plant development and biomass production. Soil pH is characterized as substantial variations in soil acidity or alkalinity. The pH of soil is affected by both acidic substances and ions that constitute the foundation of soil. Common cations that form acidic ions include hydrogen (H+), aluminum (Al3+), and iron (Fe2+ or Fe3+). On the other hand, typical cations that form basic ions include calcium (Ca2+), magnesium (Mg2+), potassium (K+), and sodium (Na+). Earthworms contribute to pH alteration (5%) and, in conjunction with microbial decomposition, help maintain a lower pH in vermicast (Elvira et al., Panjgotra et al., 2019) [32] . The researcher analyzed the soil pH and found that the majority of the soil in the region is alkaline, as shown in Table (). The northern part of the Doaba region, including the Hoshiarpur region, has soil that is slightly acidic in nature. This could be attributed to the higher rainfall in this area compared to the rest of the Doaba region. This information is supported by studies conducted by Jatav et al. (2013) [15] and Sunita et al. (2020). The soil in the southern and western parts of the Doaba region is classified as slightly to moderately alkaline, according to studies 2009 [16] by Rafie et al. (2021) [34] , Bhusan et al. Majha region range from acidic to strongly alkaline, with the majority of the land classified as moderately alkaline to slightly alkaline. Kaur et al. (2014) [18] found that the soil pH in the district of Amritsar ranged from slightly alkaline to high alkaline. This finding was also supported by Singh et al. (2020) [48] , Sharma et al. (2019) [43] , Kaur et al. (2019) [19] , Singh et al. (2016) [47] , and Panjgotra et al. (2019) [32] . Similarly, Bhatt and Singh (2017) [4] and Bhatt and Singh (2021) [3] observed similar results in Tran Taran. The soil in the Gurdaspur district has a pH level that ranges from slightly acidic to slightly alkaline, as indicated by the investigation reports of Sekhon (2012) [40] [11] .

The fluctuation in pH levels in the Malwa region may be attributed to the alterations in soil composition, namely the presence of Inceptisols and Inceptisols-Aridisols. The majority of districts in the Malwa region have a moderate alkaline composition. In their investigation, Harmandeep et al. (2008) observed that the Malwa region has a slightly alkaline and strong alanine composition. Elbaalawy et al. (2006) [11] discovered that the district of Barnala, Bhatinda has a pH level of moderate alkalinity. Similar findings were reported by Singh et al. (2016) [47] and Yadav et al. (2020) [55] . Some researchers have also discovered that the districts of Faridkot, Ferozpur, Mansa, and Barnala have a high alkaline content. The references cited are Kang, et al., (2010) and Verma et al., (2008) [52] . The remaining districts, including Moga, Mansa, and Ludhiana in the Malwa area, have a slightly alkaline nature. The following studies have been conducted: Panjgotra et al. (2019) [32] , Mittal et al. (2020) [30] , Singh et al. (2007) [44] , and Elbaalawy et al. (2006) [11] . The districts of Fazilka, Faridkot, Muktsar, and Bhatinda in southwestern Punjab feature aridisols and entisolsaridisols soil orders. These soil types have little water holding ability, leading to soil accumulation and increased pH levels.

Electrical Conductivity

The electrical conductivity of the solution is directly linked to the presence of fully charged cations or anions in the solution.

The ions present in soil solution can be classified as cations (Ca++, Mg++, K+, Na+, H+) or anions (NO3-, SO4-, Cl-, HCO3-, CO3-, OH-). Electricity is commonly used to determine the salt content of the earth. However, it may also be used to measure the amount of soluble nutrients, including both cations and anions. Therefore, within a specific range, the electrical conductivity (EC) will indicate efficient absorption of nutrients by plants, whereas the lower end will indicate nutrient-deficient and readily scattered soils, as well as issues with salt tolerance. EC units are commonly expressed as mhos/cm, mmhos/cm, or 1/1000 mhos/cm, which are equivalent to Siemens per meter (S/m) or Deci Siemens meter (dS/m). The link between these two units is millimhos per centimeter equals deciSiemens. [42] , Singh et al., (2016) [47] ; Bhat and Singh (2020) [5] , Panjgotra et al., (2019) [32] .

In the malwa region, the soil's electrical conductivity ranges from somewhat saline to non-saline. The Amritsar district is located in the central part of the Majha region and the northwestern part of Punjab. Salinity has been recorded in certain areas of the district, as documented by Singh et al.

(2020) [48] and confirmed by Sharma et al. (2019) [43] . The researchers Sekhon et al., (2012) [40] , Dhillon and Dhillon (2004) [10] , Elbaalawy et al., (2006) [11] , and Bhatt.R and singh.P have determined that the soil in the Gurdaspur and Tarn Tran districts has low electrical conductivity and is non-saline. Malwa region indicates that the soil's electrical conductivity is non-saline. The researcher has gathered data from the years 2006 to 2020 for all districts in Malwa. The data shows that the electrical conductivity levels in these districts are consistently below 1 dSm -1 , which is within the normal range. In their study, Elbaalawy et al. (2016) [11] found that the soil in different districts of the Malwa region, namely Bhatinda, Barnala, Sangrur, and Ludhiana, falls under the non-saline category. Similar results were observed in the districts of Ferozpur, Faridkot, Fathegarh Sahib, Mansa, Moga, Sangrur, Ludhiana, and Rupnagar by Singh et al. (2016) [47] , Kang et al. (2009) [16] , Kumar et al. (2020) [25] , Verma et al. (2005) [51] , Panjgotra et al.

(2019) [32] , Elbaalawy et al. (2016) [11] , and Walia, M. K., & Walia, S. S. (2011) [53] . Sekhon et al. (2012) [40] . The researchers Kaur, R., & Goyal, D conducted a study in Rupnagar district to analyze a soil sample taken near the Guru Gobind Singh Super Thermal Power Plant in Ropar. The results showed that the soil had a small salinity, which is likely due to pollution from the ash produced by the thermal plant's industrial waste. The non-saline electrical conductivity refers to the range of soil salinity that does not have any detrimental impact on plants in terms of soil salinity and crop tolerance.

Organic carbon

In order to promote soil fertility, plant protection, and agricultural sustainability, soil organic carbon is an important indication of soil health. There are two types of carbon in soil: organic carbon, which is found in organic matter, and inorganic carbon, which is abundant in carbonate minerals. Soil carbonate minerals, which are present at the start of parental activity, are formed during melting, hence not all soils contain inorganic C. All agricultural soil contains organic carbon, though. When the soil is dry and composed of calcareous parent material, the inorganic concentration often exceeds the organic C content. The carbon found in soil is an element of the soil's organic composition. Carbon accounts for most of the organic matter's mass (58%), with water and various nutrients like potassium and nitrogen making up the rest. Soils that are rich in organic carbon provide several benefits, including improved water retention, increased microbial activity, a lower pH, regulation of various soil physiochemical properties, and a more favorable response to nitrogen fertilizer. Composted organic materials, such as animal manure, compost, etc., can be applied to soil. Soil organic matter decreases as one moves down the slope, because of balance. Most of the soil in the Doaba region is within the medium category in terms of organic carbon content. The researchers' studies are provided in tables. The organic carbon content in soil ranges from 0.09% to 1.0%. Except for the southern part of the Doaba region, the district of Kapurthala has soil with a medium to high organic carbon concentration.

There is a favorable correlation between high levels of organic carbon in soil and agricultural productivity. Singh (2016) [49] and Bhat and Singh (2020) [5] . All remaining districts, namely Hoshiarpur, Jalandhar, SBS Nagar, and Nawan Shahar, exhibit low to medium levels of organic carbon. The following studies have been referenced: Kukal et al. (2004) [20] , Jatav et al. (2013) [15] , Sharma et al. (2017) [42] , Surya et al. (2019) [50] , Panjgotra et al. (2019) [32] . The soil in the Majha region generally has a moderate level of organic carbon concentration. The researcher Singh et al. (2016, 2020) [47] discovered a high concentration of organic carbon in the soil in Amritsar district, followed by medium levels in Tran Taran. Bhatt. R and Singh.P (2017) [4] and Bhatt, R., & Singh, M. (2021) [3] also found similar results. In Gurdaspur, the soil has a low organic carbon content. Paul et al. (2012), Dhillon et al. (2004) [10] , and Elbaalawy et al. (2006) [11] . The data acquired from the research conducted in the Malwa region indicates that almost half of the region has a soil organic carbon level ranging from high to medium. While the southern middle part of the Malwa region has districts like Barnala, Bhatinda, Ferozpur, and Faridkot with medium to low range, the analysis conducted by Singh et al., Elbaalawy et al., (2016) [11] Yadav et al., (2016) [56] and Kumar et al. (2016) [24] reveals that these districts are classified as high and medium range respectively. The researcher's data collection in the eastern half of the Malwa region reveals that the districts of Mansa, Moga, Sangrur, Ludhiana, and Rupnagar (Ropar) have a low organic carbon content in the soil. The presence of low organic carbon in soil indicates poor soil fertility and unstable physical properties. The cause of this low organic carbon content may be attributed to various factors such as different soil orders found in different regions of Punjab, including aridisols and Entisols-aridisols, as well as practices like stubble-burning and inadequate management of crop residues.

Nitrogen

Nitrogen is crucial for plants as they require it in significant amounts. Additionally, supplying nitrogen can be quite costly, and it is prone to being lost from the soil. Nitrogen primarily exists in the form of proteins and nucleoproteins, with minor and diverse quantities of amines, amino acids, polypeptides, and several other molecules. The predominant nitrogenous chemicals are primarily found in the protoplasm and nucleus of plant and animal cells. Among them are enzymes, which are proteins that accelerate biological processes. Each plant cell needs more nitrogen molecules to achieve optimal rates of reproduction, growth, and respiration (Robertson and Groffman 2024) [37] . The chlorophyll found in green leaves, which allows plants to utilize sunlight to synthesize sugar, starch, and carbon dioxide in water, is composed of nitrogen compounds. Many non-nitrogen molecules, closely associated with nitrogenous chemicals, act as a potent energy source for numerous biological processes. Certain non-protein nitrogen compounds may not exhibit significant biological activity, but they are expected to largely serve as components of the body's structure, like cellulose and lignin (Niazifar et al., 2024) [31] . One example is chitin, a complex organic compound linked to carbohydrates. It is present in microorganisms, fungi, parasites, and in the exoskeletons of crustaceans and insects. Nitrogen is mostly present in the delicate and tender portions of plant tissues, such as the apical meristems, buds, and nascent foliage (Kumar et al., 2024) [21] . Nitrogen, primarily present in the form of proteins, undergoes continuous movement and chemical transformations. During the process of cell formation, a significant amount of protein can be transferred from older cells to newly formed ones, particularly if the plant's overall nitrogen levels are insufficient. Subsequently, the plant optimizes its utilization of the limited resources.

Nitrogen is an indispensable component present in plants derived from the soil, playing a vital role in promoting plant development (Li and Gao 2024) [26] . Nitrogen gas constitutes approximately 80% of the Earth's atmosphere. Nitrogen gas is dissolved in water, where it undergoes conversion by blue algae into ammonia, which is utilized by the algae. Inorganic nitrogen and ammonia can infiltrate ponds and streams as forms of nitrogen. Due to the various pathways through which nitrogen can infiltrate water systems, there is a plentiful supply of nitrogen present in these systems. Earthworms enhance Nmineral digestion by actively mineralizing carbon, such as decaying plant roots and leaf litter, during the process of gut passage (Barron et al., 2024) [1] . [15] found that in the Hoshiarpur district, the accessible nitrogen in the soil ranged from 186.3 to 3556 kg ha -1 , which falls within the low to medium range. In SBS Nagar, researchers Shilpa Panjgotra et al.

(2019) [32] and S. [18] , Singh et al. (2020), Sharma et al. (2019) [43] , Panjgotra et al. (2019) [32] , and Bhatt, R., & Singh, M. (2021) [3] . An investigation of the Malwa region revealed that the nitrogen content in the soil was found to be insufficient for optimal plant growth, specifically in the Bhatinda district. Yadav et al. (2020) [55] reported that the available nitrogen in the soil ranged from 26 to 325 kg ha -1 , which falls within the medium range. This trend was observed in the remaining districts of Fathegarh Sahib, Moga, Ludhiana, and Rupnagar. The researcher's findings have a limited range. The following references were cited: Kumar et al., (2020), Panjgotra et al., 2019 [32] , Hargopal, S., & Pritpal, S (2011) Walia, M. K., & Walia, S. S. (2011) [53] , Kaur, R., & Goyal, D (2015) [19] . Most of the Punjab's territory suffers from a lack of nitrogen content, indicating the need for increased use of nitrogenous fertilizers to enhance crop production. Additionally, there is a need to improve crop residue management to increase organic matter in the soil, which in turn stimulates microbial activity and indirectly increases the availability of nitrogen. Bhatt and Sharma (2011) observed that almost 65% of samples from district Kapurthala had a low potassium status, with available potassium levels below 137.5 kg/ha. Researchers have observed that the potassium level in soil in the Majha region is predominantly medium to high. The researcher Rana.P (2020) [35] found that 44% of the region in Amritsar is classified as high range. Similarly, Sekhon B.S et al. (2012) [40] discovered that Gurdaspur has a similar percentage. In district tran tarn, Bhatt. R and Singh. P (2017) [4] , Bhatt, R., & Singh, M. (2021) [3] reported a yield of 258.2Kg/Ha. The chosen researcher in the Malwa region investigates the variability of potassium levels in soil across different districts. However, the majority of districts fall within a certain range. The districts of Bhatinda, Faridkot, and Mansa have a high potassium level, while the districts of Ferozpur, Moga, and Fathegarh Sahib have a medium potassium content. Researchers Hargopal, S., & Pritpal, S, Walia, M. K., & Walia, S. S. (2011) [53] observed that certain districts in the Malwa region have a low potassium level in the soil, specifically in the Ludhiana district. In the study conducted by Barnala Singh, S., & Benbi, D. K. (2016).

Phosphorus

Conclusion

The different physicochemical features of the soil in Punjab contribute to a wide spectrum of agricultural productivity. The main objective of this research was to analyze the soil condition in the Punjab region. The findings indicated that the soil properties of the three regions exhibited substantial dissimilarities. The soil chemical properties of the Doaba region were determined to be superior compared to those of the Majha and Malwa regions. The Doaba region exhibited moderate soil nitrogen levels, but the Majha region displayed low levels. Implementing effective soil management practices in the Malwa region of Punjab was necessary. The Majha region typically has a moderate level of alkalinity in its soil, whereas districts like Amritsar and Tarn Taran have localized areas with significant alkalinity. The soil pH in this area varies from moderately acidic in the northern parts to strongly alkaline in the southwestern parts. Although certain industrial areas, like Amritsar, may have slightly elevated salt levels, the electrical conductivity (EC) measurements indicate that the overall environment is not excessively saline. Consequently, this makes it suitable for cultivating a diverse range of crops. The organic carbon content in soil varies significantly, ranging from extremely low to extremely high. The regions of Majha and Malwa have the highest prevalence of this wide range, resulting in better soil fertility. However, areas with low levels of organic carbon indicate a necessity for improved management of crop wastes and organic additions. When nitrogen availability is predominantly low to medium, it becomes evident that there is a requirement for improved soil management practices and higher levels of nitrogenous fertilization. Due to the elevated phosphorus concentration, it is crucial to apply appropriate fertilization methods to prevent nutritional imbalances. This is particularly important in Majha and certain areas of Doaba and Malwa. In addition, there are variations in potassium levels in different regions of Malwa. Some areas in Malwa have insufficient potassium levels, requiring specific soil amendments, while Majha region has moderate to high levels of potassium. Ultimately, the study of soil dynamics in Punjab reveals that the interplay between natural and human factors has complex effects on the physicochemical characteristics. In order to maintain agricultural output and soil health in this everchanging agricultural environment, it is crucial to comprehend and regulate these transformations by employing specific fertilization strategies and implementing novel soil management techniques.

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