A method of coordinating the operation of a singling device and the operation of a portioning device of an agricultural application machine with each other to achieve a preset local placement relationship (Δx) when depositing seed grains singulated by the singling device and fertilizer portions produced by the portioning device onto an agricultural area, comprising the steps of: - depositing singled seed grains and produced fertilizer portions onto the agricultural area by means of the agricultural application machine in the course of a calibration travel; and - detecting the placement positions (P K, P P) of the seed grains and fertilizer portions deposited during the calibration travel and/or their local placement relationship (Δx K) by means of a mobile testing device; wherein a control system, which is connected to the singling device and/or the portioning device in a signal-conducting manner, imposes an operating behaviour on the singling device and/or the portioning device at least temporarily in order to achieve the preset local placement relationship (Δx) of seed grains and fertilizer portions, which the control system determines on the basis of the placement positions (P K, P P) of the seed grains and fertilizer portions detected by means of the mobile testing device and/or their local placement relationship (Δx K); characterized in that - the mobile testing device comprises an electronic measuring wheel and an actuating device, wherein the measuring wheel is moved by an operator along a placement path and the placement positions (P K, P P) of the seed grains and fertilizer portions and/or their local placement relationship (Δx K) are detected by manual actuation of the actuating device; or - the mobile testing device is an electronic image recording device, wherein the placement positions (P K, P P) of the seed grains and fertilizer portions placed during the calibration travel and/or their local placement relationship (Δx K) are recorded via an evaluation of one or more image recordings of the mobile testing device of the seed grains and fertilizer portions placed during the calibration travel. - depositing singled seed grains and produced fertilizer portions onto the agricultural area by means of the agricultural application machine in the course of a calibration travel; and - detecting the placement positions (P K, P P) of the seed grains and fertilizer portions deposited during the calibration travel and/or their local placement relationship (Δx K) by means of a mobile testing device; wherein a control system, which is connected to the singling device and/or the portioning device in a signal-conducting manner, imposes an operating behaviour on the singling device and/or the portioning device at least temporarily in order to achieve the preset local placement relationship (Δx) of seed grains and fertilizer portions, which the control system determines on the basis of the placement positions (P K, P P) of the seed grains and fertilizer portions detected by means of the mobile testing device and/or their local placement relationship (Δx K); characterized in that - the mobile testing device comprises an electronic measuring wheel and an actuating device, wherein the measuring wheel is moved by an operator along a placement path and the placement positions (P K, P P) of the seed grains and fertilizer portions and/or their local placement relationship (Δx K) are detected by manual actuation of the actuating device; or - the mobile testing device is an electronic image recording device, wherein the placement positions (P K, P P) of the seed grains and fertilizer portions placed during the calibration travel and/or their local placement relationship (Δx K) are recorded via an evaluation of one or more image recordings of the mobile testing device of the seed grains and fertilizer portions placed during the calibration travel. - the mobile testing device comprises an electronic measuring wheel and an actuating device, wherein the measuring wheel is moved by an operator along a placement path and the placement positions (P K, P P) of the seed grains and fertilizer portions and/or their local placement relationship (Δx K) are detected by manual actuation of the actuating device; or - the mobile testing device is an electronic image recording device, wherein the placement positions (P K, P P) of the seed grains and fertilizer portions placed during the calibration travel and/or their local placement relationship (Δx K) are recorded via an evaluation of one or more image recordings of the mobile testing device of the seed grains and fertilizer portions placed during the calibration travel.