A novel test methodology for evaluating prescription-map-based ISOBUS variable rate sprayers in viticulture

The use of variable rate application (VRA) technology enables spatial- and demand-oriented application of plant protection products, thereby facilitating precise and efficient plant protection in viticulture. However, there is a lack of standardised test methods for validating dynamic application volume rates for VRA sprayers in specialty crops. This paper presents a test methodology to evaluate the performance of ISOBUS-compliant VRA sprayers using prescription maps by comparing prescribed and applied spray volumes under controlled test bench and real field conditions. Therefore, four different test scenarios were developed for both environments to enable a systematic assessment of dynamic variable rate behaviour, including fixed (Scenario 1) and variable application volume rates under varying driving speeds (Scenario 2) and prescribed volume rate levels (Scenario 3). Depending on the scenario, the applied spray volumes derived from manual reference measurements, ISOBUS task logs and external flow sensor data (Scenario 4) were compared with each other. Overall, the developed test scenarios offer a first structured approach to assess the performance of VRA sprayers under controlled test bench and field conditions. In the first three scenarios, RMSE values below 5 % indicate that manual reference measurements and ISOBUS task log data provide a consistent and reproducible basis for assessing VRA behaviour along entire vine rows. In contrast, flow measurements using external sensors positioned downstream of the PWM nozzles showed higher deviations (RMSE ≤ 7.7 %) under highly dynamic conditions, demonstrating limitations for accurate applied spray volume assessment in the present experimental configuration.