Evaluating and Improving the Performance of the Models Underlying the Soil Navigator Tool on Drained Peat Grasslands

The Soil Navigator Tool is a decision support system designed for farmers and advisors to assess the capacity of a selected field to perform five soil functions: primary productivity (PP), water regulation (WR), habitat provision (HP), climate regulation (CR), and nutrient cycling (NC). The original tool was developed and validated primarily with mineral soils as the focus. In this paper, we tested and updated the underlying models of the Soil Navigator Tool for the context of drained peat grasslands. The performance of both the original and updated models was evaluated using input and validation data originating from 30 peat grasslands situated in the north of the Netherlands, managed either as semi-natural grassland, organic production grassland, or conventional production grassland. For PP, only minor changes were made to the original model. Both versions produced reasonable assessments with respect to yield. For WR, the sub-function Water Storage (WS) was updated, yielding scores that are more in line with soil moisture measurements from these drained peat grasslands. Only minor changes were applied to the original model of HP. As a result, the performance improved on conventional production grasslands, but the model still struggles to accurately assess semi-natural grasslands. For CR, major changes were applied to the sub-function carbon sequestration (CS) to accurately represent carbon cycling on drained peat. The updated version produced more reasonable outcomes than the original, especially on conventional production and semi-natural grasslands. Despite major changes to the original model of NC, both versions performed poorly, suggesting the need for a completely new model with a depth and time component to accurately account for peat oxidation. Our outcomes suggest that the updated models generally produce more reasonable outcomes than the original models on drained grassland peat. However, more research to further improve and validate the updated models is needed, with a particular focus on NC, before the use of the Soil Navigator Tool on drained grassland peat by farmers or researchers is recommended.