A method and a system in an agricultural machine for the coordination of agricultural machines when refilling substance intended to be disseminated over an agricultural field by generating coordination data indicative of an optimum refill location, comprising a level sensor arranged for generating level data, said level data indicating a volume of a substance in a substance reservoir； a position sensor for generating and storing position data and storing or reading a preplanned route； a communication device arranged for transmitting and receiving data； characterised by: a coordination device generating coordination data, based on said level data, said preplanned route and said position data； and transmitting said generated coordination data via the communication device to a refill vehicle.
