In Germany decisions on lime application rates are based on pH values measured in manually collected soil samples (normally one sample per field). Although in-field soil pH variability might be considerable even at short distances this is not taken into account due to costs for sampling and analysis so far. Using the on-the-go soil pH mapping system Veris MSP developed in the USA spatial soil pH variability can be measured at high spatial resolution. However, reliable information on how to use this data for decisions on liming rates under German conditions is not available. Therefore lab and field trials to evaluate the on-the-go pH-measurement were conducted in north-western Germany from 2009 to 2011.

After adaptation of the Veris MSP system to German farm technology the online measured pH values were validated against lab data for several fields. A survey based on 30 fields with sandy to loamy soil texture (field size 2 – 45 ha) revealed that the difference between minimum and maximum pH usually was higher than one pH unit. The spatial pattern for soil pH values within a field was comparable for both procedures. However, pH sensor data were not identical with the results from the German lab procedure and were generally higher especially for pH values below 6. A software based strategy to collect reference soil samples for lab analysis from zones with low, medium and high Veris MSP pH values was developed. Based on lab pH values for these reference samples a linear function for each field can be calculated to convert online measured pH values into standardized values for using them in the existing German lime recommendation schema. In 2011 this variable lime application strategy was compared to standard farm practice with a uniform lime rate.