Comparative Assessment of Physicochemical Variation of Soil Profiles Across Lowland and Upland Topographies in Mahewa District, Prayagraj, India

Abstract

Topography influences soil physicochemical properties, directly impacting land management in the Indo-Gangetic Plains. To understand these effects, this study compared soil profiles from lowland and upland sites in the Mahewa district, Prayagraj, India. Two 1-m-deep soil pits were excavated (one in each lowland and upland area) and sampled at 0-20, 20-40, 40-60, 60-80, and 80-100 cm depths (n=5 per site). The properties analyzed included pH, organic carbon (OC), available nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), electrical conductivity (EC; indicates soluble salt content), and carbonate, using standard methods. Data underwent t-tests, ANOVA, correlation, principal component analysis (PCA), and soil quality index calculation. The results showed that lowland soils were characterized by higher available phosphorus (P; 25.4±1.3 vs 20.0±0.8 mg/kg; P=0.010), calcium (Ca; 2.34±0.12 vs 1.72±0.08 cmol(+) kg⁻¹; P=0.004), iron (Fe; 12.0±0.3 vs 8.64±0.3 mg/kg; P<0.05), and soil quality index (SQI; 0.73 vs 0.59), while potassium was numerically higher in the lowland (K; 119.8±17.9 vs 94.6±6.7 mg/kg) when compared to upland soils. Both locations had a neutral pH (around 7.0), indicating neither acidity nor alkalinity. Strong correlations were observed for organic carbon-nitrogen (OC-N; r=0.98), clay-silt (r=0.82), and pH-phosphorus (pH-P; r=0.71). Principal component analysis (PCA) results distinguished texture/fertility factors (PC1) from depth-related factors (PC2), confirming that topography significantly affected most examined properties (ANOVA, P<0.001). These findings suggest that topography influences soil heterogeneity in Mahewa; lowlands exhibit higher nutrient levels and higher overall SQI. Site-specific management may enhance sustainable agriculture in this region.