Abstract: The invention relates to a device for mixing a liquid such as fertilizer with water flow in a sprinkler pipeline where the liquid is timely dispensed over a period of time from a fertilizer chamber into a mixing chamber for mixing with the water before re-entering the pipeline. The device has a flexible diaphragm that sealingly separates a mixing chamber from a fertilizer chamber. A central disk is fixedly carried by the diaphragm and is biased by a first spring that applies a restoring force upon displacement of the central disk. A valve seat on an axial extension of the central disk extending into the mixing chamber is so dimensioned and proportioned to seat a pin holder fixed to an adjuster holder upon engagement by the pin holder. The adjuster holder is responsive to a second spring and the water pressure in the mixing chamber.