Pedo‐Climatic Controls on Soil Health Recovery Across Cultivation Chronosequences: Hydraulic Conductivity as a Potential Link Between Soil Structure, Microbial Biomass, and Nutrient Availability

ABSTRACT Long‐term cultivation can improve soil health, but recovery may not follow the same pathway across contrasting soil and climate conditions. A key unresolved question is whether soil health recovery is mainly associated with the release of physical–chemical constraints or with the gradual rebuilding of carbon, microbial biomass, and nutrient‐retention capacity. We compared cultivation chronosequences in two contrasting pedo‐climatic systems, referring to distinct combinations of soil type and climate regime: semi‐arid saline–alkaline soils in Egypt and tropical slightly acidic soils in South Sudan. Uncultivated, 10‐year cultivated, and 30‐year cultivated soils were compared in both systems. Saturated hydraulic conductivity (HC), bulk density (BD), salinity–sodicity indicators, soil organic carbon (SOC), cation exchange capacity (CEC), microbial biomass, and nutrient availability were measured in the biologically active surface layer (0–30 cm). Across the chronosequences, SOC increased by 127%–160%, total nitrogen by 150%–400%, and microbial biomass by 126%–257%, indicating broad improvement in soil fertility and biological functioning in both systems. However, recovery followed contrasting pathways. In the semi‐arid soils, HC increased by 244%, while electrical conductivity, sodium adsorption ratio, and BD declined by 60.4%, 62.4%, and 14.2%, respectively, suggesting recovery associated with the release of salinity‐, sodicity‐, and compaction‐related constraints. In the tropical soils, HC increased by 201%, but recovery was more closely associated with SOC accumulation, higher CEC, microbial biomass development, and nutrient retention. Modeling analyses were consistent with this interpretation: HC‐centered structural equation modeling showed better fit than alternative structures, HC was positively associated with microbial biomass across systems ( β = 0.61–0.70, p < 0.01), and Random Forest identified HC among the important variables linked to microbial and nutrient indicators. Thus, HC may provide a context‐dependent diagnostic signal of soil recovery, reflecting structural–hydraulic accessibility in the semi‐arid soils and SOC‐linked functional development in the tropical soils. These findings support a diagnostic approach to soil health assessment, in which key indicators are interpreted according to the dominant recovery constraint within each pedo‐climatic system.