Swine manure application methods effects on ammonia volatilization, forage quality, and yield in the Pre-Amazon Region of Brazil

The use of swine manure (SM) 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. The objective of this study was to evaluate SM 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, Maranhão, Brazil, and the following SM application methods were evaluated: (1) surface application, (2) incorporation at 5-cm soil depth, (3) incorporation at 10-cm soil depth, and (4) control when SM was not applied. Lower N losses due to NH3 volatilization and higher pasture yield and quality were found when SM was incorporated at 10-cm soil depth (83 kg N-NH₃ ha^-1 and 6.3 Mg DM ha^-1, respectively, compared to 86 kg N-NH₃ ha^-1 and 1.5 Mg DM ha^-1 for the control), whereas higher N-NH3 losses and lower pasture yield were observed when SM was applied to the soil surface (143 kg N-NH₃ ha^-1 and 2.6 Mg ha^-1, respectively). Higher quality forage in terms of chemical composition was also observed when SM was incorporated at greater soil depth. Incorporating SM at 10-cm depth represents an efficient management to mitigate N-NH3 volatilization, and this application method is associated with significantly increased in DM yield and improved chemical composition.