Abstract: A chemical mixing and metering apparatus is provided which can be easily incorporated into existing irrigation lines. The apparatus includes a venturi which is positioned along an irrigation supply line. The venturi is connected to a chemical supply container by a chemical conduit and by a bypass conduit. A valve is positioned in the bypass conduit to regulate the flow of irrigation fluid from the irrigation supply line into the chemical supply container. A check valve or vent is provided in the container to prevent formation of a vacuum. The chemical mixing and metering apparatus is operable in two modes of operation. Firstly, the apparatus may be operated as a vacuum system by closing the valve in the bypass conduit. Secondly, the system may be operated in a force feed/vacuum mode by opening the valve in the bypass conduit. Moreover, the apparatus may be used to inject solid and/or liquid chemicals into an irrigation system.