Phosphorus Dynamics and Their Relationship with Soil Properties in Soils of Tasawa Agricultural Project, Fazzan-Libya

Abstract

This study evaluates the influence of soil physicochemical properties on the distribution and dynamics of total phosphorus (TP) and available phosphorus (AP) in cultivated and uncultivated soils of the Tasawa agricultural project. Soil samples were collected from five cultivated circuits and three reference sites and analyzed for pH, electrical conductivity (EC), organic matter (OM), cation exchange capacity (CEC), soil texture, TP, and AP using standardized laboratory methods. Both cultivated and uncultivated soils exhibited slightly alkaline pH values (7.72–7.86), which provided a basis for interpreting other soil characteristics. EC was elevated in cultivated soils (234.44–311.15 mS/m) compared to reference soils (213.22 mS/m), suggesting increased ionic content associated with agricultural activity. OM content was also higher in cultivated soils (1.97–2.54%) than in reference soils (1.90%). CEC values were marginally lower in cultivated soils (18.35–20.60 meq/100 g) relative to the reference (21.39 meq/100 g). The soils were predominantly sandy (>82%), resulting in low nutrient retention and influencing phosphorus distribution. TP concentrations were higher in cultivated soils (36.99–96.00 mg/kg) than in reference soils (29.54 mg/kg). AP levels remained consistently low (1.95–4.49 mg/kg) across all samples, indicating substantial phosphorus fixation. Multivariate statistical analysis revealed significant positive correlations between OM and TP, sand and AP, and pH and AP. Principal component analysis (PCA) accounted for 72.93% of the total variance, identifying four principal components: soil texture, organic matter, mineral composition, and ionic environment. Cluster analysis confirmed the strong association between OM and TP, and emphasized the roles of soil texture and pH in determining phosphorus availability. Analysis of variance (ANOVA) indicated significant differences (p < 0.05) among soil properties and phosphorus forms, whereas EC did not differ significantly. In summary, phosphorus behaviour in these soils is governed by the interactions among soil texture, pH, and organic matter. These results highlight the complexity of phosphorus dynamics in sandy arid soils.