Corn response to pig slurry and nitrogen fertilization in areas highly fertilized with organic manure

Two field experiments were carried out from 2000 to 2004 in Chapecó and Guatambu, State of Santa
Catarina, Brazil, to evaluate the effect of pig slurry and N fertilizer on yield of corn cultivated under no tillage in an Oxisol. The experimental design was randomized block with treatments set in split plots and three replications. The main plots received pig slurry (zero, 40 and 115m3/ha) broadcasted on the surface or incorporated in furrows (40m3/ha). In the subplots, the annual N fertilizer (zero, 60 and 120kg/ha) was split in 1/3 at corn sowing
and 2/3, 45 days later. In Guatambu, in most growing seasons, corn yields increased linearly with the N fertilizer rates. The response to pig slurry without N fertilizer was quadratic in all seasons. The maximum yield was obtained with 85m3/ha of pig slurry. In Chapecó, on a soil that had received pig slurry for a long time, the N fertilizer had little effect on corn yield. There was no difference in corn yield between the application methods of pig slurry.