Soil surface crusting has major implications for agricultural production and environmental quality due to its effects on crop establishment, soil hydrological properties and erosion. The impacts of crusting are more deeply felt in the semi-arid tropics (SAT) where low inherent soil fertility, water availability, and population pressures already pose serious problems. The objectives of this study were, therefore, to: (1) assess field surface soil properties linked to crusting under various cropping and management; (2) to examine crust effects on runoff and interrill erosion processes; and (3) to establish the crusting mechanism(s) based on crust characteristics and micromorphology. The research was conducted in two parts: a field study in India; and a laboratory experiment at OSU.;An accumulation of fine particles in crusts formed under a wide range of treatment conditions reflected the formation mechanisms (pore filling and rain compaction) operating in the sandy Alfisol. Water stability of aggregates and water dispersible clay content suggested a decline in structure due to tillage, which appeared to reverse by late season due presumably to consolidation and drying. Infiltration rates indicated rapid loss of the benefits of tillage due to surface crusting. Termite activity increased infiltration by increasing macroporosity, the nature and continuity of which appeared to be influenced by cropping and residue type. Surface soil strength depended on soil moisture and surface micro-variability. Micropenetration resistance was related to extent of crust development and degree of drying.;Plowed soil aggregates were more susceptible to rapid sealing and erosion under laboratory rain simulation than naturally vegetated soil. However, runoff and total soil loss increased dramatically once seals formed on both soils. Sealing notably increased soil flow and splash detachment for short rainfall durations. Initial aggregate stability and extent of seal development were the primary determinants of total soil loss. Structural crusts 2-4 mm thick formed by a 5-stage process involving: mechanical aggregate break down by rain drops; aggregate slaking leading to dispersion of fine soil material; translocation and deposition of fine material; rain drop compaction and rearrangement of particles in the seal layer; and reorientation of clay causing bonding and rigidity of the crust upon drying.
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