Phosphorus Availability and Potential Environmental Risk Assessment in Alkaline Soils

Soil phosphorus (P) is an essential element that is often limiting in ecosystems. Excessive use of P fertilizers has led to P loss from soil and introduction into the environment. However, the behavior and potential risk assessment of P in alkaline soils is not well studied. Therefore, soil sampling was performed in alkaline soils in the northern Nile Delta, Egypt. Three analytical procedures (i.e., Mehlich 3 (PM3), Olsen (POlsen), and Bray 1 (PBray) solutions) were used to evaluate P availability and potential environmental risk from P loss. Selected soil properties were determined using standard methods. Mean values of P extracted were in the order PM3 > Polsen > PBray, and were significantly correlated with each other. The PM3 was the highest in silt clay loam and lowest in sandy and loamy soils. To predict potential P loss from the soils, degree of P saturation (DPS), soil P storage capacity (SPSC), and P stability ratio (Psat) were calculated. Results showed the highest DPS was recorded in sandy textured soils, indicating that they have lower sorption capacity, whereas the SPSC was highest in silt clay textures; hence, it is likely they would act as a P sink. Psat was highest in sandy soils, which indicated a high risk for P leaching. Principal component analysis (PCA) performed on the data identified four principal components that described 83.8% of the variation between P and the studied soil parameters. The results indicated that silt was the critical soil characteristic associated with both P sorption and extractability in different textures of soil. The second component confirmed the positive association between the different soil P extraction methods (PM3, POlsen, and PBray).