Gaseous Emissions after Soil Application of Pellet Made from Composted Pig Slurry Solid Fraction: Effect of Application Method and Pellet Diameter

The study aimed at determining ammonia and GHG emissions from soil fertilized with pellets made from composted pig slurry solid fraction and to evaluate the effects of pellet diameter and pellet application method on gaseous emissions. A laboratory scale experiment was carried out investigating two composts: pig slurry solid fraction compost (SSFC) and pig slurry solid fraction mixed with wood chips compost (WCC). The two composts were pelettized in two different diameters—6 and 8 mm—by means of mechanical pelletizer. In total, eight fertilized treatments plus one unfertilized control were included in the experiment. The investigated pellets were applied at the same nitrogen rate (equivalent to 200 kg ha −1 ) using two different methods (on soil surface and incorporated into the soil). Ammonia (NH 3 ) emission was monitored immediately after pellet application, while nitrous oxide (N 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) were measured on a 57-day incubation period. As expected, ammonia volatilization was not detected from any of the treatments investigated. At the end of the experiment, the cumulative amounts of N 2 O, CO 2 and CH 4 ranged from 2.70 mg N-N 2 O m −2 to 24.30 mg N-N 2 O m −2 , from 601.89 mg C-CO 2 m −2 to 1170.34 mg C-CO 2 m −2 and from 1.22 mg C-CH 4 m −2 to 1.31 mg C-CH 4 m −2 , respectively. The overall results of the investigation highlighted that application on the soil surface reduced nitrous oxide emission, while the carbon dioxide emission increased significantly with smaller pellet diameter.