Physic-Chemical and Structural Properties of an Oxisol Under Straw and Limestone Addition.

Liming represents a common agricultural practice in abating soil acidity. Nevertheless, elevated doses of limestone in Oxisols, with or without cultural residue addition, could alter soil physico-chemical properties and impact soil structure. In this context, the physical, chemical and structural behaviors of an Oxisol under the addition of limestone and straw were assessed. Limestone doses (0, 3.9, 7.8, and 15.6 Mg ha^-1) were either applied on the surface or incorporated into the 0-to-5 cm soil layer. Straw applications followed the same procedure with quantities of 0, 4, 12, and 16 Mg ha^-1. The effects on the soil profile were evaluated through physico-chemical (specific surface area, zeta potential, and pH), physical (density, penetration resistance, water dispersible clay, and total porosity), and micro-morphological (surface area, volume, connectivity, size and pores anisotropy) properties during one year after soil incubation in 30 cm long and 14.5 cm PVC cylinders. Limestone application on the surface or into the 0-to-5 cm layer increased soil pH to values above 7.0 and electronegative potential of soil colloid surface, promoting clay dispersion. Water-dispersed clay migrated in the soil profile, causing pore obstruction, and higher soil density and resistance to penetration. In addition, excessive liming decreased specific surface area, anisotropy degree and the connectivity of the soil pore system. Straw addition promoted a slight increase of colloids electronegative potential, but did not alter soil physical properties.