Are soil quality indicators good predictors for agricultural yield?

Soil quality scoring is a useful tool in land management as it can help determine the most suitable land use and is used to estimate the value of land for agricultural or forestry production. In agriculture, soil scoring can also help to inform management practices such as fertilizer application and irrigation rates, or even determine taxation levels as is the case in Germany. Various indicator-based soil scoring systems exist, and are often claimed to be linked to crop yield potential as an important ecosystem service.  In Germany, a system more than 100 years old called the Bodenschätzung is still used today and provides the most detailed soil information system for agricultural land across Germany. Calculating the Bodenzahl (soil score) with this method requires expert knowledge, is only applicable to German soils and does not consider climate variables such as mean annual temperature and precipitation. The Müncheberg Soil Quality Rating (MSQR) is an emerging method developed in Germany in 2007 which attempts to make yield potential scoring simpler, more widely applicable and more accurate. This system claims to be usable without extensive training and was suggested to be globally applicable by some previous studies. It also considers climate variables such as drought risk and soil temperature regime that may allow for more accurate yield predictions than soil-only methods like the Bodenzahl. However, there is little evaluation on the relation between soil quality indicators and yield. Therefore, we tested the implementation of the MSQR system and calculated MSQR scores for 3104 sampling points from the first German Agricultural Soil Inventory following the MSQR guide. In addition, we tested the performance of the Bodenschätzung with the Bodenzahl for the sampling points and related these soil quality indicators with 10 years of point specific yield data from our data set.  Preliminary findings suggest that the MSQR may determine yield potential and yield stability better than the Bodenschätzung, likely due to the fact that climate variables are considered. However, MSQR parameters may need to be adjusted locally for the method to accurately predict yields in different regions, which makes a global application of the method more complex. In general, soil indicators seem to predict only part of agricultural yield at national scale with management practices and climate still playing important roles.