Assessing on-farm soil health indicators under Norwegian conditions

Summary

Farmers and advisors seek simple methods to monitor soil health. Here, we assessed the performance of different soil health tests on the top soil (0-10 cm) of different agricultural “habitats”, from an organically managed grassland to a conventional potato production in Norway. In each production system, grassland and potato, we selected different areas where variations on soil health were expected. In the grassland, a gradient from cultivated to permanent pasture was selected. In the conventional potato field, plots that received different organic materials (biochar, digestate, farmyard manure) two years prior to the soil assessment, were selected. The tests were performed in early summer 2021 (June) for the grassland, and in summer 2021 (July) after the harvest of early potatoes in the potato field. The tests comprised different aspects of soil health: soil organic matter content (ignition loss), labile soil carbon fractions (Active C), soil biology (microbiology and mesofauna) and soil biological activity (soil respiration and feeding activity) and soil aggregate stability. Test results were used to compare the systems and the areas within the systems. Overall, the tests significantly differentiate between organically managed pasture and conventional potato field, with the first showing better values for soil health. However, the tests did not significantly differentiate between areas/treatments within the production systems. Yet, in the organically managed grassland, permanent pasture showed a trend of better soil health than cultivated areas. In the conventional potato field, selected soil health tests were not sensitive to capture the residual effects of the organic amendments, and untreated and treated soil showed very similar values. To be able to visualize the results together, we normalized the data by diving single values by the maximum value observed for each soil indicator within each system. By doing so, we obtained an overall soil health diagram that can be easily interpreted by farmers and advisors. The use of several simple tests together showed to be valuable also to inform about soil health within the to two production systems. Yet, a visual evaluation of the topsoil and chemical nutrient analysis is recommended to complement these tests. Furthermore, we need more field data to obtain “reference levels” for these tests, that would help with the interpretation of their results in the future.