A method for monitoring and/or adjusting an active agent concentration in a spray liquid to be deployed via a spray device for agricultural purposes, an active agent and a carrier liquid being fed to a mixing unit of the spray device in order to blend the spray liquid. The method includes: receiving a first property signal including a piece of property information of the blended spray liquid detected using a first sensor unit, to ascertain an actual value of the property information of the spray liquid； receiving a second property signal including the piece of property information of the supplied carrier liquid detected using a second sensor unit of the spray device to ascertain a base value of the property information of the carrier liquid； and outputting an information signal to a display unit and/or a control signal to a delivery unit of the spray device.
