Land capability studies using GIS techniques in the northern dry zone of Karnataka (Sathihala sub-watershed, Vijayapura)

Introduction

Land is a finite and invaluable resource that forms the foundation for all material production. When used rationally and judiciously, it has the potential to meet the needs of a growing population. However, in many parts of India, the current state of land use and management remains a serious concern, especially for those working at the grassroots level. Approximately 51% of the country's total geographical area is available for agriculture, and more than 60% of the population continues to depend on agriculture for their livelihood. This limited agricultural land is increasingly under stress due to rising population pressure and competing demands from various land uses. Each year, significant portions of farmland and water resources are diverted to non-agricultural purposes (Sehgal et al., 1990) [12] . Additionally, a growing disinterest in farming among rural communities has contributed to an alarming increase in fallow cultivable land across several regions.

Watershed management programs aim to address these challenges through comprehensive strategies such as soil and water conservation, enhancing the productivity of existing crops, promoting crop diversification with horticultural species, rehabilitating wastelands through multipurpose forestry, and improving livelihood options for landless households. Achieving these goals requires the preparation and implementation of a well-structured, site-specific Natural Resource Management (NRM) plan. The cornerstone of such a plan is the development of a Land Resource Inventory (LRI), which provides detailed insights into the resource potential and constraints of a given area. An LRI involves the detailed characterization and mapping of land resources, including soil, climate, water availability, geological formations, vegetation types, cropping patterns, land use, socio-economic conditions, infrastructure, market access, and ongoing government programs (Naidu et al., 2006) [9] . Farmlevel data collection enables the identification of locationspecific problems and opportunities, supporting the scientific planning of conservation measures, assessment of land suitability for various uses, and the formulation of sustainable, site-specific land-use strategies tailored to individual landholdings (Katyal et al., 2003) [4] . The district of Vijayapura, located in the northern part of Karnataka, lies within the Northern Dry Zone (Agro-climatic Zone 3) of the state. Spanning an area of 10,541 km², it is situated between 15°50′ and 17°28′ N latitude and 74°54′ and 76°28′ E longitude. Vijayapura is bordered by Yadgir district to the east, Kalaburagi district to the northeast, Bagalkot district to the southwest, and the state of Maharashtra to the northwest. The region's geology comprises formations from the Deccan Traps, the Bhima Group, and the Peninsular Gneissic Complex. Agriculture in Vijayapura is predominantly rainfed, with cotton, maize, groundnut, chickpea, and various pulses as the principal crops. However, horticultural cultivation remains relatively limited in the area (Shivaprasad et al., 1998) [14] .

Methods

Description of the Study Area

The study was conducted in the Sathihala sub-watershed (4D5C5n), located in Devara Hipparagi taluk of Vijayapura district, Karnataka. Geographically, it lies between 16°28′20″ and 16°30′50″ North latitude and 75°51′50″ and 76°55′50″ East longitude, covering an area of approximately 9,531.65 hectares. The sub-watershed is bounded by the villages of Devara Hipparagi, Sathihala, Utthnala, Rabinala, Bommanahalli, Dindawar, Ingaleshwara, and Aralichandi. The region falls under the hot, dry, semi-arid ecoregion (ESR) of the North Karnataka Plateau and southwestern Maharashtra. Soils are predominantly shallow to medium loamy black soils, with pockets of deep clayey black soils. The area exhibits moderate to high available water capacity (AWC), and the length of the growing period (LGP) ranges from 120 to 150 days. This agro-ecological zone extends over the entire districts of Koppal, Vijayapura, and Bellary, as well as parts of several other districts, including five taluks of Belagavi, six of Bagalkot, two of Raichur, one of Dharwad, one of Davanagere, and four of Gadag. The total geographical area of this zone is approximately 8.94 million hectares. Most of the region lies at an elevation between 450 and 800 meters above mean sea level (MSL), with some areas reaching up to 900 meters. Average annual rainfall in this zone ranges from 464.5 mm to 785.7 mm. The predominant soil types are medium and deep black clays in most areas, with sandy loams occurring in some parts. The main cropping season is rabi, and principal crops include maize, bajra, groundnut, cotton, wheat, sugarcane, and tobacco.

Soil Survey and Mapping

A comprehensive soil survey was conducted in the study area using high-resolution satellite imagery from IRS-LISS IV and Cartosat-1, at a scale of 1:8,000, supplemented by topographic sheets of Vijayapura district. The survey followed the methodology prescribed under the Land Resource Inventory (LRI) framework. Systematic field traverses were carried out to document surface characteristics such as soil texture, slope, erosion status, gravelliness, calcareousness, and stoniness. Surface soil samples were collected at 320-meter grid intervals and analyzed for key parameters including macro-and micronutrient status, electrical conductivity (EC), soil reaction (pH), and organic carbon content. To assess subsurface variability, pedon sites were selected based on observed surface heterogeneity. Soil profiles were excavated at each site, and detailed morphological descriptions of individual horizons were recorded. Samples from each horizon were analyzed for essential physical and physicochemical properties using standard analytical procedures. Based on correlation and interpretation of soil properties, the soils were classified into four distinct soil series according to the classification system outlined in the Field Guide for Land Resource Inventory, Sujala-III Project, developed by ICAR-NBSS&LUP. These soil series were further delineated into 74 unique mapping units, differentiated by variations in texture, depth, slope, and erosion characteristics.

Land Capability and Soil Suitability Assessment

Soil-site characteristics of the various soil units were determined by calculating the weighted average of each soil property, which was then interpreted to assess land capability. These properties were compared with criteria outlined for land capability classification (Table 1). The land capability classification is organized into three primary categories: i) Capability Unit: Categorizes soils with similar responses to cultivated crops and pasture plants, often determined by their respective yields. ii) Capability Subclass: Groups capability units sharing similar types of limitations and hazards. iii) Capability Class: Groups soils based on the degree of limitations, escalating from Class I to VIII. Classes I to IV are suitable for cultivation, whereas Classes V to VIII are not suitable for cultivation but may be appropriate for grazing, forestry, wildlife maintenance, recreation, or watershed protection (ICAR, [6] ).

In the present study, land capability classification was undertaken primarily based on the third category (Class III) of the established classification system, which considers inherent soil properties, external landform characteristics, and relevant environmental factors. The delineation of land capability classes and subclasses was conducted following the methodological guidelines in the LRI Field Guide of the REWARD project, developed by ICAR-NBSS&LUP [7] . Using advanced Remote Sensing (RS) and Geographic Information System (GIS) technologies, various thematic layers were generated, overlaid, and subjected to spatial analysis to develop comprehensive land capability and soil-site suitability maps. This analysis was performed using the ArcView interface within the ArcGIS 10.8.2 software environment. Comparable approaches have been employed in previous studies by Suryawanshi et al. [8] , Mishra et al. [9] , Mishra and Babu [10] , and Mary Silpa and Nowshaja [11] .

Results and Discussion Soil Map and Soil Mapping Units

A soil map visually represents the spatial distribution of different soil types and mapping units in relation to major physical and cultural features of the Earth's surface. In this study, soil mapping units were identified using input parameters such as soil series, texture, depth, slope, erosion status, and gravel content.

The study area was classified into 26 distinct soil series: Algali (AGL), Atharga (ARG), Arthal (ATL), Baramkodi (BKD), Deginal (DGN), Dadamatti (DMT), Halahalli (HHL), Hunashyal (HSL), Hattararkihal (HTK), Jayawadagi (JYD), Kalgurki (KGR), Karjol (KRJ), Masabinal (MBL), Managoli (MGL), Nandihal (NDL), Naihalla (NHL), Kamanakeri (NRG), Rambapur (RMB), RPR, Sankanala (SKL), Tenihalli (THL), Tonsihal (TKL), Thalewada (TLD), Dadamatti (TNL), Tonsihal (TSL), and Yambatnal (YBT) (Table 2). Among these, the Tonsihal series occupies the largest area, covering 1,454 ha (38.16%). These soils are very deep (>150 cm), poorly drained, and range from sandy clay to clay in texture. They occur on gravelly, gently sloping uplands under cultivation. The Karjol series covers 485 ha (12.21%) and is characterized by very deep, poorly drained, non-gravelly soils of similar texture on gently sloping midlands. The Nandihal series, covering 445 ha (11.67%), consists of very deep, poorly drained, gravelly soils ranging from clay to sandy clay texture, located in gently sloping lowlands. The Baramkodi series, covering 255 ha (6.68%), comprises deep (100-150 cm), poorly drained, nongravelly clay soils found in very gently sloping lowlands. A total of 74 unique soil mapping units were delineated using the ArcView interface of ArcGIS 10.8.2 software (Fig. 1). These units were grouped into 14 mapping categories, derived during various stages of soil series delineation. The legend for the mapping units follows a structured nomenclature. For example:

DMTiB2g1

• DMT: Soil series (Dadamatti)

• i: Surface texture (sandy clay)

Land Capability Classification

Based on the soil-site characteristics, the soils were classified into two Land Capability Classes (LCC), as summarized in Table 3.

Moderately Suitable Soils

Approximately 3,228 ha (84.71%) of the Sathihala subwatershed falls under Land Capability Class III (Fig. 3). These soils are moderately suitable for cultivation but possess certain limitations that may restrict agricultural productivity. Key limiting factors include:

• Shallow soil depth [13] .

Marginally Suitable Soils

About 447 ha (11.74%) fall under Land Capability Class IV, which includes soils with severe limitations, primarily due to erosion, runoff, and shallow depth. These soils are fairly suitable for occasional cultivation or alternative land uses because of: . Sustainable management practices for Class IV soils include terracing, strip cropping, contour tillage, and integration of perennial vegetation or permanent cover crops. As noted by Amara et al. (2016) [1] , cultivation on such soils should ideally be rotated with pasture, hay, or orchard systems to prevent degradation and reduce erosion risk.

Acknowledgement

AcknowledgementThe authors sincerely thank the Watershed Development Department, Government of Karnataka, for financial support provided under the REWARD project, which enabled this study in the Sathihala sub-watershed. We also express gratitude to ICAR-NBSS&LUP, Bengaluru, for their technical guidance and support throughout the investigation.

References

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