Manure Application Methods in Pastures to Reduce Nitrogen Loss By Ammonia Volatilization and Increase Forage Quality and Yield in the Pre-Amazon Region of Brazil.

The use of swine slurry as a nutrient source for pastures is increasingly common in Brazil, due to its low cost. However, this practice can cause N losses in agricultural soil, where ammonia (NH₃) volatilization may be the main drawback, generating undesirable economic and environmental consequences. This study aimed to evaluate PS application methods that retain N within the system and determine how these methods affect forage yield and quality. The study was conducted in the municipality of Chapadinha, MA, Brazil, and the following three swine slurry application methods were tested: (1) application on the soil surface, (2) incorporation at 5-cm soil depth, and (3) incorporation at 10-cm soil depth; also, (4) as a control, a pasture with no application of PS was tested. Lower nitrogen losses due to NH₃ volatilization and higher pasture yield were found when swine slurry was incorporated at 10-cm soil depth (83 kg N-NH₃ha^-1 and 6.3 Mg dry matter ha^-1, respectively, compared to 86 kg N-NH₃ ha^-1 and 1.5 Mg dry matter ha^-1 for the control), whereas higher N-NH3 losses and lower pasture yield were observed when swine slurry was applied to the soil surface (143 kg N-NH3ha^-1 and 2.6 Mg ha^-1, respectively). Higher-quality forage in terms of chemical composition (was also observed when PS was incorporated at greater soil depth. Incorporating swine slurry at 10-cm depth represents an efficient way to mitigate N losses from the system due to N-NH₃ volatilization, and this application method is associated with significantly increased dry matter yield and improved chemical composition.