Until recently in-field variability for soil pH could not be considered for agronomic decisions (e.g. liming rates) because reliable spatial information was hardly available. The required density of soil pH-measurements could not be achieved by manual soil sampling due to time constraints and analysis costs for the vast number of samples. A comprehensive on-the-go soil pH mapping system (Veris-MSP) has been developed during the last years, but data on the performance under German conditions are not available.

After adaptation to German farm technology this system was validated at the experimental farm of the University of Osnabrueck on several fields. The VERIS-MSP was equipped with two ion-selective antimony electrodes for pH-measurement. Based on the Kriging-method pH values were interpolated to generate pH-maps for individual fields. Additionally, manual soil samples were collected and analysed in the lab to validate the accuracy of the pH sensor data. The relationship between Veris-MSP and lab data was assessed by regression analysis.

Field tests confirm that the VERIS-MSP works precise after fine-tuning the system. A sampling density of 10-50 samples/hectare had been realized depending on speed (5-10 km/h) and spacing between passes (5-20 m) in the field. Usually the difference between minimum and maximum pH for an individual field is higher than one pH unit and the spatial variability of soil pH can be converted into a pH-map which offers opportunities for management adaptations. The correlation coefficient between pH sensor and lab data is high (r²=0.79). However, pH sensor data are generally higher than lab pH values and pH values below 6 seem to have a lower relationship.

In proceeding field trials the pH-online-system will be further validated (e.g. robustness of antimony electrodes; reproducibility of measurements; impact of soil conditions). Furthermore the economical return of management decisions based on pH-mapping will be compared with standard farm practice.