A GIS-based Approach to Assessing the Spatial Variability and Rhizosphere Soil Properties of Retama raetam Forssk., Growing in Southern Algeria

Abstract

Fabaceae shrubs like Retama raetam L. can reshape soil chemistry through rhizosphere-microbe interactions, yet their spatial effects in arid lands remain underexplored. The main objective of the study is to assess and quantify the interactions of rhizosphere soil associated with Retama raetam and its spatial variability in the Sebseb region, Algeria. Rhizosphere (RS) and bulk soil (BS) were sampled and analyzed for pH, electrical conductivity (EC), organic matter (OM), CaCO₃, available phosphorus (AP), mineral nitrogen (NO₃), total nitrogen (TN), and soluble/total sodium and potassium (SNa/TNa, SK/TK). RS-BS contrasts, correlations, and spatial structure were assessed using variograms and ordinary kriging. RS/BS comparison revealed significant differences in several characteristics. EC (p < 0.0001), CaCO₃ (p < 0.0001), and TN (p = 0.0069) were higher in BS. RS exhibited a significantly lower pH (p < 0.0001), while NO3 (p = 0.01) and TK (p = 0.01) levels were higher.  All variables fit Gaussian variograms, except EC, pH, SNa, and TNa, which were better fitted in spherical models; nugget: sill <25% indicated strong spatial dependence. Kriging maps revealed nutrient hotspots (EC, NO₃, AP) and broader pedogenic patterns (CaCO₃, pH) across Sebseb soils. Rhizosphere soil had lower pH and higher NO3, while bulk soil harbored more CaCO₃, EC, and TN, highlighting distinct biological and pedogenic processes. Geostatistical analysis indicated strong spatial dependence, with short-range variability linked to rhizosphere effects and longer ranges driven by environmental factors. Overall, Retama raetam enhances nutrient availability and soil fertility, supporting its role in sustainable land management.