Spatial variability of soil boron in a boron-rich agricultural plain using GIS

Soil properties and nutrient levels vary spatially due to natural and anthropogenic heterogeneity, and their spatial assessment using geographic information systems (GIS) and geostatistical methods can support sustainable agricultural management. Boron (B) is an essential micronutrient for plant growth; however, it may accumulate in soils and become toxic even at relatively low concentrations. This study investigated the concentration and spatial distribution of plant-available B in the soils of the Mustafakemalpasa Plain, a major agricultural area developed on alluvial deposits derived partly from a B-rich upstream basin. A total of 238 soil samples were collected from 119 locations using a 1.5 × 1.5 km grid-based sampling design at two depths: topsoil (0-30 cm) and subsoil (30-60 cm). Plant-available B was extracted using 0.01 M CaCl₂ and determined spectrophotometrically by the azomethine-H colorimetric method at 420 nm. Spatial distribution maps and prediction standard error maps were generated using ordinary kriging in a GIS environment, and B concentrations were classified according to established soil fertility thresholds. In addition, selected soil properties and CORINE land-use/cover data were used to evaluate potential factors associated with B distribution. The results revealed considerable spatial variability in B concentration. In the topsoil, 55% of the area exhibited high B levels, while 40% showed moderate concentrations. In the subsoil, 56.60% of the area was classified as moderate and 32.41% as high in B. Correlation and regression analyses indicated that B distribution was associated with multiple soil properties, particularly topsoil texture, moisture, pH, and subsoil EC. CORINE-based area analysis further showed that elevated B classes were more frequent in agricultural areas, although land use alone had limited explanatory power. Overall, the findings indicate that a substantial portion of the Mustafakemalpasa Plain is affected by elevated B levels. Considering the geomorphological connection of the plain with B-rich upstream deposits and the dominance of agricultural land use, site-specific monitoring and management strategies are needed to reduce potential B toxicity risks and support long-term soil and crop productivity.