Spatial Variability of Soil Properties in a Walnut Ecosystem of the Kashmir Himalaya

Abstract

Digital soil mapping has emerged as a powerful tool for generating detailed soil information in time and cost-efficient manner with better accuracy and higher spatial resolution. The present study was conducted during 2024–2025 at the Walnut Research Station, Kulangam, Kupwara district of Jammu and Kashmir, India, to assess the spatial variability of soil physico-chemical and biological properties for improving site-specific nutrient management in walnut (Juglans regia L.) growing soils. Despite the economic importance of walnut cultivation in the region, spatially explicit information on soil properties remains limited, constraining precision nutrient management. A total of 110 geo-referenced soil samples were collected on a 30 × 30 m grid and analyzed using standard laboratory procedures. Spatial interpolation and thematic map generation were carried out using ArcGIS software. The results revealed that soils were predominantly loam to clay loam in texture, with pH ranging from 6.13–7.49 and low electrical conductivity (0.05–0.15 dS m⁻¹), indicating non-saline conditions. Organic carbon ranged from 0.92–1.15% and cation exchange capacity from 17.02–21.14 cmol(p⁺) kg⁻¹. The available macronutrient contents (kg ha-1) ranged from 220.12 to 410.04 for nitrogen, 8.98 to 37.13 for phosphorus, 140.27 to 457.28 for potassium, and 10.01 to 36.51 for sulphur. Exchangeable calcium and magnesium contents varied between 4.12–5.16 cmol(p⁺) kg⁻¹ and 2.36–2.62 cmol(p⁺) kg⁻¹, respectively, indicating adequate base saturation. Among DTPA-extractable micronutrients, iron (Fe), manganese (Mn) and copper (Cu) were found to be generally adequate across the study area. However, zinc (Zn) deficiency was observed in more than 50% of the sampling locations, highlighting it as a critical limiting nutrient for walnut productivity. Microbial populations followed the order: bacteria > actinomycetes > fungi, indicating biologically active soils. Overall, the study underscores the effectiveness of digital soil mapping in delineating spatial variability of soil properties. The generated nutrient maps provide a robust scientific basis for precision nutrient management, facilitating improved input-use efficiency and sustainable walnut production in temperate agro-ecosystems of Kashmir.