An additive material storage and metering system includes a transportable frame having a plurality of dry material storage bins mounted thereon. The plurality of dry material storage bins includes smaller material storage bins and larger dry material storage bins. The metering system for the larger dry material storage bins has a flow rate range varying from a low end to a high end. The metering system for the smaller dry material storage bins has a second flow rate range varying from a low end to a high end. The low end of the second range is lower than the low end of the first range, and the high end of the second range is between the low and high ends of the first range, so that any given dry material may be dispensed at any rate within an overall flow rate range from the low end of the second range to the high end of the first range by placing said material in the proper dry material storage bin. The metering systems each include a metering bin for receiving material from one of the storage bins, a conveyor for discharging material from the metering bin, and an air lock between the conveyor and a discharge line. Various other refinements in the metering systems are provided.