Aggregate Stability And The Influence Of Sodium Chloride On Dispersion Of Sandy Clay Loam Soils In Southeastern Nigeria

Abstract

Soil dispersion is an important process that should be considered in irrigation and ferti-irrigation of agricultural soils. Triplicate topsoil samples from five different locations in southeastern Nigeria were characterized and examined for aggregate stability and clay dispersion potential by leaching with different NaCl concentrations. The results showed that the soils were mainly sandy clay loam (SCL), slightly acid to neutral pH and low in soil organic carbon (SOC), total nitrogen, and exchangeable cations. The soils had lower proportions of > 1.00 mm water-stable aggregates (WSA) compared to the higher proportions of < 1.00 mm WSA. Percent aggregate stability (AS) of the soils averaged 36.25 % and was significantly positively correlated with SOC (r = 0.55*) and Na⁺ content (r = 0.58*). Furthermore, Na⁺ correlated positively with the 1.00-2.00 mm WSA (r = 0.67*), but negatively with the < 0.25 mm WSA fraction (r = -0.68**), while the opposite was true for the correlation of clay and these WSA fractions (r = -0.57*; 0.60*, respectively), indicating the minor role of clay in aggregate formation. The soils were less dispersible in water than in NaCl solutions, resulting in a higher clay content, which increased with increasing NaCl concentration. However, the clay dispersion ratio of the soils was moderately low and showed a decreasing trend with increasing NaCl concentration, and indicating the NaCl dispersion potential at the lowest 25 S m^-1. Thus, the clay dispersion potential of Na⁺ at ≤ 50 S m^-1 relates to the reduced stability of < 0.25 mm microaggregates, while the clay flocculation potential of Na⁺ at ≥ 75 S m^-1 accounts for the 1.00-2.00 mm macro aggregation and aggregate stability of the soils. Therefore, the structural stability of SCL soils in the humid tropics depends on SOC and Na⁺ content, including the dispersive and flocculative influence of Na⁺ on clay minerals.