Abstract: A metering unit for soil and plant improvement agents to increase the water absorption capacity of the soil, comprises a first inlet connector that can be connected with a watering line, a second outlet connector that can be connected with a watering line, a flow channel that runs between the inlet connector and the outlet connector, a bypass channel that branches off from the flow channel in a flow direction, leads into a mixing chamber for admixing a soil or plant improvement agent, and opens into the flow channel again from the mixing chamber, and a metering valve disposed in the flow channel, the metering valve regulating both flow-through amount through the flow channel and flow-through amount through the bypass channel at the same time.