There is a paucity of information on the long-term effects of crop residue management under no-tillage culture on properties of clay soils in tropical and subtropical regions. The objective of this study was to compare the effects of 13 yr of conventional tillage vs. no tillage, crop residue retained vs. burned, and no fertilizer N vs. application of 23 and 69 kg N ha-1 yr-1 on organic C content, total N, mineralizable N, pH, electrical conductivity, chloride, exchangeable sodium percentage (ESP), and aggregation index (undispersed fraction <20 fim silt + clay) in a fine-textured Vertisol (650 g clay kg-1 soil). Highest concentrations of organic C and total N were found in the surface soil (0-0.1 m) with a combination of no-tillage, crop residue retained, and fertilizer N. Mineralizable N followed similar trends. Soil pH to 0.3-m depth and electrical conductivity to 1.2-m depth were significantly lower under no-tillage than under conventional tillage. Aggregation index of the surface soil (0-0.1 m), was higher under no-tillage. The ESP was lowest in the surface soil (0- 0.04 m) under no-tillage with crop residues retained; the soil profile (0-1.2 m) under this treatment also contained far less NaCl-equivalent salts (0.8 Mg ha-1) than under conventional tillage with crop residue burned (7.3 Mg ha-1). Available water and nitrate were lower in the surface soil but greater at depths (0.6-1.2 m) under no-tillage than in tilled soil. Thus tillage and crop residue management can substantially affect soil organic matter and microbial activity in the surface layers, and water relations and salt movement to at least 1.2-m depth, even in a fine-textured Vertisol.
