Root-restricting layers in German agricultural soils. Part II: Adaptation and melioration strategies

Aims In many agricultural soils in Germany, elongation of deep roots is restricted by compactness, anoxia and acidity. This study examined the adaptation and melioration strategies of farmers who cultivate sites with such root-restricting layers (RRLs). Methods The German Agricultural Soil Inventory was evaluated with respect to land use and crop rotations on sites with and without RRLs. The likelihoods of deep tillage, drainage and liming and the feasibility of biological melioration (bio-drilling) were predicted using soil, geology, climate and socioeconomic data. Results Anoxic and acidic sites were preferentially used as grassland. Cropland with RRLs was often dominated by maize instead of wheat. About 54% of agricultural land in Germany was limed, 45% drained, 6% deep chiselled and 5% deep ploughed. The abundance of biopores was positively related to silt content and pH, but negatively related to rock content. Conclusions Deep tillage is not very popular for alleviating soil compactness, but bio-drilling could be used to facilitate deeper rooting in loamy and well-aerated soils with low rock fragment contents and pH values >5. Waterlogged soils could be meliorated by improved drainage and extreme acidity by enhanced liming practices. However, many farmers preferred grassland use as opposed to meliorating RRLs.