Spatial Assessment of DTPA-Extractable Cationic Micronutrients in Calcareous Alluvial Soils of Vaishali District, Bihar, India

Abstract

This study investigated the spatial distribution and availability of DTPA-extractable cationic micronutrients in calcareous alluvial soils of Vaishali district, Bihar, India. A total of 139 geo-referenced surface soil samples (0–15 cm) were collected using a grid-based sampling approach covering major administrative blocks. Soil physicochemical properties, including pH, electrical conductivity (EC), and organic carbon (OC), were analyzed along with DTPA-extractable zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) following standard procedures. Soils were predominantly neutral to moderately alkaline (pH 7.02–8.36; mean 7.95) with low salinity (EC 0.11–2.48 dS m⁻¹; mean 0.31 dS m⁻¹) and low to medium organic carbon content (0.21–1.21%; mean 0.54%). Available Zn ranged from 0.14 to 2.43 mg kg⁻¹ (mean 0.91 mg kg⁻¹), with 45.32% of samples below the critical limit (<0.78 mg kg⁻¹), indicating widespread zinc deficiency. Iron content varied from 4.35 to 32.78 mg kg⁻¹ (mean 14.37 mg kg⁻¹), with 64.43% of samples in the high category. Manganese ranged from 2.27 to 5.99 mg kg⁻¹ (mean 3.41 mg kg⁻¹), where 38.85% of samples were deficient. Copper content (0.47–1.47 mg kg⁻¹; mean 0.70 mg kg⁻¹) was largely adequate, with more than 75% of samples in the medium range. Descriptive statistics revealed moderate variability in micronutrient distribution across the district. Correlation analysis indicated weak to moderate relationships among soil properties and micronutrients, including a positive association between EC and Cu (r = 0.297) and a moderate negative relationship between Fe and Mn (r = –0.399). The results highlight significant spatial heterogeneity and emphasize the need for site-specific micronutrient management, particularly zinc fertilization, to sustain soil fertility and enhance crop productivity in calcareous soils of the Indo-Gangetic plains.