# Rapid Soil Tests for Assessing Soil Health
## 1 Introduction
Though there is now broad agreement about the importance of soil health and its assessment, and the need for proper sampling protocols to tackle spatial soil heterogeneity, there are still discussions about (i) the selection of relevant soil properties and processes (soil indicators), (ii) the methods used to quantify these indicators, (iii) the linkages between the indicators and soil ecosystem services (i.e., soil health outcomes), and (iv) about the integration, i.e., how to determine the relative contribution of the various indicators to an overall soil health score [7; 39; 40]. As soil is multifunctional, a relatively wide range of different indicators is needed [7; 39; 40], but more indicators often mean more costs for soil analyses, which suggests that a balance is needed here. There is especially discussion about the selection of appropriate soil biological indicators [40]. Next to proper soil sampling, relatively large costs are related to quantitative soil analyses, depending on methods. Recent advances in analytical techniques and methods have greatly broadened the range of soil properties that can be measured easily and the speed of analyses, but new methods and procedures do not necessarily match with the existing knowledge base related to conventional soil analyses methods and users [41; 42]. A main challenge is linking the soil health indicators to soil health outcomes, i.e., soil ecosystem services, especially following soil management interventions, as there is a paucity of studies that have tried to do so in practice in different landscapes and environments. The need for integration of soil indicators into an overall soil indicator score likely depends on the user of the score and the spatial scale [7; 39]; policy makers of (supra-)national organization may embrace a'simple' score for ease of communication, but growers and land managers may be more interested in an overview of single soil indicators to base management decisions. Also, a recent comparison of different integrated soil health assessment tools revealed that different tools may give different soil health indices [43], which is not helpful for generalizations. Evidently, there is need for further elaboration and testing of soil health indicators, and for monitoring projects to measure the soil health baseline status and changes in soil health over time. Routine soil testing in agricultural, urban and natural areas is as yet scarce. Even when soil testing of cropland is routine in some countries, often only a limited number of soil characteristics are measured, often reflecting soil fertility testing and not soil health testing [44, 45]. Comprehensive routine soil health testing is not common, because commonly agreed soil health assessment tools are not yet well established, as discussed above, and because several different tests and methods are needed, which are often laborious and expensive to conduct. Furthermore, some laboratory tests require chemicals, dangerous to human health and the environment [46, 47]. Innovative soil tests may overcome the limitations of some of the current routine soil tests and may be used to create soil health test reports that increase the guidance value of soil testing. A universal soil health test report would help stakeholders, including governmental agencies of different countries and multinational agrifood industries, to explain the soil test results. It is well accepted that the many different soil testing methods across countries make it very difficult to compare the results of soil health testing and the impacts of for example improved agroecological approaches [48, 49]. The aim of this study was to contribute to the further development, implementation, and testing of an integrated procedure for soil health assessment in practice. We selected more than 50 soil properties pertinent to soil health. These properties were assessed through an innovative three-step analytical approach, which was tested across 15 countries.