This invention describes a mobile system (101) for optimising the fertilizing value of a slurry, such as a liquid manure, where said mobile system is mounted on a mobile unit (103) and comprises a slurry tanker (105, 107) where said slurry tanker comprises a container (105) and a slurry conduit (107), where said slurry tanker is in liquid communication with acid adding means (111, 113) for adding/injecting an acid to said content of said slurry tanker, where said slurry tanker and/or acid adding means is in liquid communication with distributing means (110) for allowing a modified slurry to be placed on the application site, and where said slurry conduit transports a content of said slurry tanker from said container to said distributing means, wherein said mobile unit comprises at least one nitrogen tank (109) containing a liquid nitrogen-containing composition and nitrogen injecting means (238, 239, 240) for adding said liquid nitrogen-containing composition to said content of said slurry tanker.
