An important base for adequate liming is the recording of the soil pH. Several studies indicated a large heterogeneity of soil pH within fields. Recently technological improvements facilitate an on-the-go determination of the soil pH in a much higher sampling density compared to the conventional, time consuming and costly laboratory method. The “Veris soil pH sensor” allows georeferenced on-the-go mapping of the soil pH. But the “Veris soil pH sensor” and the widely accepted laboratory method differ in their measuring principles. Hence it is necessary to adapt the results of the pH sensor to the results of the laboratory method. A suitable algorithm for calibration of the on-the-go recorded data has been evaluated and presented by the authors at the ICPA (2012).

The economic potential of high resolution soil sampling strategies compared to the conventional soil sampling strategies is determined by four effects: the costs of applying the technology, the cost savings resulting from the reduction of over-fertilisation, the improved exploitation of phosphate (which will become plant-available due to small scale pH management) and the expected increase in yield (and thus revenues) resulting from a better lime distribution. To quantify the four effects, on-farm experiments were carried out the results of which are presented. In the on-farm field trials four different soil sampling approaches were compared: (1) one ha fixed grid, (2) five ha fixed grid, (3) “intelligent” apparent electrical conductivity homogenous sampling zones, (4) high resolution soil sampling. The impact of the four approaches on profitability was calculated for a six-year crop rotation. The costs of the technology, the cost savings resulting from the reduction of over-fertilisation and the improved exploitation of phosphate occur only once within the six years. The expected yield effects, however, must be taken into consideration six times within the crop rotation.

The analysis of the field trials shows that sampling density is crucial for the reduction of over- and under-supplied zones. According to the conventional sampling method (5 ha fixed grid) approx. 32 % of the area was over-fertilised and approx. 38 % under-fertilised. The “intelligent” soil sampling showed similar results. The reduction of over-fertilisation was equal to a value of approx. 20 € / ha, which can be saved or better distributed. An improved lime distribution resulting from high resolution soil sampling increases the amount of plant-available phosphate and leads to an increase of yield. Corresponding savings amount to approx. 32 € / ha for the phosphate which must not be fertilised. The increase of yield generates increased revenues of approx. 15 € / ha (annually). The costs for applying technology add up to 20 € / ha for the pH sensor, whilst the conventional procedures (fixed grids) cause costs between 2 and 13 € / ha.

Briefly summarized, the field trials indicate an annual economic advantage of 15 - 30 € / ha of the high resolution soil sampling compared to conventional soil sampling.