Stipendiatstilling 1 NIBIO (2020-2023)

Soils provide several ecosystem services such as food production, carbon storage and water filtration. However, soil degradation threatens the delivery of soil ecosystem services worldwide. Soil health implies that the physical, chemical and biological components of the soil are functioning optimally. However, to measure and improve soil health, a system for monitoring is needed where climate, type of land use and the soil is considered. The overall aim is to increase knowledge of soil health assessment in Norway, determine optimal soil health in different pedo-climatic zones and to assess the effect of cropping systems on soil health. The thesis is finalized and will be sent for evaluation to Wageningen UR in February 2025, with anticipated defense May 2025. The thesis shows the advance knowledge on soil health and provides recommendations for integrative soil health assessments. A mechanistic understanding should be incorporated into soil health assessments to guide the selection of soil indicators at broader scales. Additionally, the thesis investigates measures to improve soil health in Norway, addressing a significant gap in the literature regarding farmers' adoption and documentation of conservation practices. A key contribution is the development of reference curves for interpreting soil indicators in Southeast and mid-Norway (Chapter 2). The findings suggest that conservation practices positively influence soil health in Southeast Norway, highlighting their potential for wider adoption. In contrast, cover crops are rarely used in mid-Norway for soil health improvement. However, this study demonstrates that substantial cover crop biomass can be achieved even at 63°N latitude (Chapter 4). Moreover, cover crops contribute to soil structure improvement, increased mineral-associated organic matter, and, to some extent, enhanced nutrient efficiency through root and microbial interactions (Chapters 4 & 5). Chapter 2 takes a pedo-climatic approach to interpreting soil indicators, while Chapter 3 assesses twelve soil indicators in an on-farm comparison of conservation and conventional practices. These indicators are conceptually linked to soil functions, with their performance evaluated against nearby reference fields and threshold values from the literature. Adaptive management approaches where practices are tested and refined should be developed in different pedo-climatic conditions to ensure (relevant) soil health improvements. The choice of plants either as main crop or as cover crops and the interaction between plants and microorganisms is important for soil health and for several soil functions. There should be an emphasis in future research for the selection of plants or cover crop species which are important for various soil functions under certain soil challenges and land-uses. Plant roots give off rhizo-deposits which are carbon-containing substances that are important for aggregate formation and for shaping the microbial community. The plant roots also release enzymes that are highly important for phosphorus- and nitrogen cycling. The majority of plants also forms symbiosis with mycorrhizal fungi which can function as an extension of the roots and obtain nutrients from deep soil layers. To promote sustainable soil health, we recommend a systems-based approach that integrates theoretical frameworks and empirical findings to advance soil health understanding. Theoretical contributions, particularly system theory, can function as a lens to interpret empirical findings, highlighting how biological, chemical, and physical components are interconnected and how these processes give rise to soil functions at the broader scale. Empirically, this work suggests how mechanistic insights—such as the role of root biomass in nutrient cycling and soil structure—can inform soil monitoring within similar context at i.e. the pedo-climatic scale.

- Adaptive management approaches where practices are tested and refined should be developed in different pedo-climatic conditions to ensure (relevant) soil health improvements. - The choice of plants either as main crop or as cover crops and the interaction between plants and microorganisms is important for soil health and for several soil functions. There should be an emphasis in future research for the selection of plants or cover crop species which are important for various soil functions under certain soil challenges and land-uses. - To promote sustainable soil health, we recommend a systems-based approach that integrates theoretical frameworks and empirical findings to advance soil health understanding. - This work suggests how mechanistic insights—such as the role of root biomass in nutrient cycling and soil structure—can inform soil monitoring within similar context at i.e. the pedo-climatic scale.