Residual effect of surface-applied lime on soil acidity properties in a long-term experiment under no-till in a Southern Brazilian sandy Ultisol

The changes in soil chemical properties caused by surface lime application depend on the application dose, reaction time, and are limited to the top few centimeters of the soil profile. The present study aimed to monitor and to interpret the impacts of surface lime re-application at different rates and splitting rates on the amelioration of soil acidity and its distribution and migration through soil profile in a sandy Ultisol from Southern Brazil under long-term no-tillage (NT) system. The experiment was installed in an area where the conventional tillage (CT) was practiced till 1988 when the soil was limed (3.1 Mg ha(-1)) and then the area was maintained under NT. In October 1994, the soil was sampled and lime was reapplied at four rates: 0, 3.6, 5.4, and 6.0 Mg ha(-1). The full dose to raise soil pH to 6.0 was applied in 1994 once. The rate of 5.4 Mg ha(-1) was split in three times, applying 1.8 Mg lime ha(-1) in 1994, 1995, and 1999, and the rate of 6.0 Mg ha(-1) was split in five times, applying 1.2 Mg lime ha(-1) in 1994, 1995, 1996, 1999, and 2000. The experimental design was randomized blocks with five replications. In October 2006 and 2012, i.e. after 18 and 24 years of the start of NT or 12 and 18 years after lime re-application (beginning of the experiment), soil samples were taken at each 1 cm depth up to 10 cm layer, each 2.5 cm depth up to 10 to 25 cm layer, and each 5 cm depth from 25 to 60 cm layer. Soil acidity attributes including active acidity (pH-H2O), aluminum (Al) saturation, exchangeable Al, exchangeable calcium (Ca), exchangeable magnesium (Mg) and base saturation were also evaluated. Results show that the re acidification of the soil is extremely slow. Even after 24 years without re-application of lime, the re-acidification process resulted in only 20% of the original potential acidity observed in the area under natural grassland. The surface application of lime in a re-acidified soil under NT promoted the formation of an alkalizing front by statistically modifying the soil acidity attributes up to 60 cm. However, it was much less deeper (< 35 cm) when considering the agronomic interpretation of the soil acidity properties. Nevertheless, for both interpretations, the lime migration and its residual behavior were proportional to the lime application rate and its split application.