Document Type : Research and Review Papers
Authors
1
soil and water, faculty of Agriculture, Sohag University
2
Division of Scientific Training and Continuous Studies National Authority for Remote Sensing and Space Sciences (NARSS) Cairo 11769 Egypt
3
Division of Soil and Water Sciences, Faculty of Agriculture, Sohag University
4
Soil and Water Department Faculty of Agriculture Sohag University Sohag 8254 Egypt
Abstract
This study evaluated the soils of Sohag Governorate, Egypt, using both traditional laboratory analysis and vis-NIR spectral data from 140 surface soil samples. Laboratory results showed wide variability in key soil properties whereas calcium carbonate (CaCO₃) ranged from 0.76% to 34.60% with a mean of 5.82%, cation exchange capacity (CEC) varied from 1.44 to 32.38 cmol(+)/kg with an average of 9.22 cmol(+)/kg, clay content ranged from 1.59% to 54.76% (mean 16.79%), and electrical conductivity (ECe) spanned from 0.38 to 30.24 dS/m (mean 4.82 dS/m). High sample variances were recorded, particularly for clay (104.66), reflecting spatial and land use diversity across old and newly reclaimed soils. Correlation analysis among these properties revealed a moderate positive correlation between CaCO₃ and CEC (r = 0.52), and weaker negative correlations between CaCO₃ and both clay (r = –0.25) and EC (r = –0.30), while clay showed a positive association with EC (r = 0.34). Spectral data collected in the 350–2500 nm range revealed distinctive spectral behaviors for each property. Soils with high CaCO₃ content exhibited increased reflectance, especially in the 2200–2350 nm region, where negative correlations reached r < –0.60. CEC showed a positive correlation with reflectance, notably around 2100–2250 nm (up to r = +0.60), due to associations with OH-bearing clay minerals. Clay content had the strongest spectral signal, with positive correlations exceeding +0.70 in the 2100–2300 nm range, while EC was moderately and positively correlated (r ≈ +0.40 to +0.50) with reflectance near 1450 nm, 1950 nm, and 2200 nm. These results confirm that the shortwave infrared region (SWIR) is particularly sensitive to variations in soil composition. The integration of vis-NIR spectroscopy with traditional methods demonstrated the feasibility of rapid, non-destructive soil characterization. The spectral approach, while dependent on calibration with laboratory data, offers significant time and cost savings for large-scale assessments. This study emphasizes the complementary value of combining conventional and spectral techniques for efficient monitoring and management of heterogeneous soils, particularly in arid and semi-arid landscapes like Sohag. The identification of key spectral bands for each property paves the way for predictive modeling and digital soil mapping, contributing to precision agriculture and sustainable land use planning.
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