Root-restricting layers in German agricultural soils. Part I: extent and cause

Aims Root-restricting layers pose a barrier to vertical root elongation. The German Agricultural Soil Inventory was used to assess the extent, cause and effect of root-restricting layers in German agricultural soils. Methods The following causes for root restriction were considered: bedrock, rock fragments, cementation, compactness, sandy subsoil, anoxia and acidity. Threshold values for restricted root growth were extracted from the literature and validated using root counts of winter wheat and permanent grassland. The effect of management-induced compaction in cropland was quantified using machine learning. Results In 71%of all agricultural soils, potential rooting was restricted to less than 100 cm depth. Compactness was the most common cause of root restriction, affecting 51% of cropland and 32% of grasslands. It was estimated that agricultural management explained 27% of all compacted cropland, while the remaining 73% has always been compacted as a result of pedogenic causes. Root-restricting soil layers decreased the yield of winter wheat significantly. Conclusions In view of potential rooting being restricted on more than half of Germany’s agricultural land and this study’s results suggesting that root-restricting soil layers have a direct impact on crop yield, there is considerable potential in the melioration of affected sites.