The objective of this work was to evaluate the nitrification rate in no-tillaged soil treated with pig slurry. The experiment was carried out during three years in an Arenic Hapludult soil, in a complete randomized block design, with split plots and three replications. The main plots were composed of two crop systems (black oat/maize and fallow/maize) and the split plots were composed of three rates of pig slurry (0, 40 and 80 m³ ha-1). The nitrification was evaluated based on concentrations of mineral N, in different soil layers, in several periods after pig slurry application. On the average of the three years, the nitrification rate in the black oat/maize system reached 4.8 kg ha-1 of NO3--N per day, overcoming that of the fallow/maize system in 43%. The application of 80 m³ ha-1 of pig slurry resulted in 188% greater nitrification rate than that observed for 40 m³ ha-1. The ammoniacal N from pig slurry is rapidly nitrified in soil under no-tillage, being completely oxidized to NO3--N from 15 to 20 days after pig slurry application.
nitrate; mineralization; crop residues
