Abstract
AimsRoot-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.MethodsThe 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.ResultsIn 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.ConclusionsIn 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.
Highlights
Root-restricting soil layers (RRLs) pose a barrier to vertical root elongation, which can severely hamper the production capacity of agricultural land
Chemical constraints to root growth occurred in 21% of all agricultural sites, with high groundwater levels affecting 14% and acidity 10% of all sites (Fig. 3f-g)
RRLs occurred mostly in subsoils, i.e. in >30 cm depth, but there was a considerable number of sites (13%) with potential limitations to root growth already occurring in topsoils
Summary
Root-restricting soil layers (RRLs) pose a barrier to vertical root elongation, which can severely hamper the production capacity of agricultural land. In soil without RRLs, subsoil resources have been shown to be of great importance for crop productivity: plant-available water stored in the subsoil can mitigate drought stress long after topsoils have dried out (Barraclough et al 1989; Kirkegaard et al 2007). Subsoils store nutrients that may contribute to plant nutrition (Kautz et al 2013) This is especially true for mobile nutrients such as nitrate, which quickly leach below the topsoil after applications of mineral fertiliser or mineralisation of organic matter (Dunbabin et al 2003; Lynch 2013). The importance of accessible subsoil water and nutrients to plant nutrition is elevated during droughts (Kirkegaard et al 2007; Lynch 2013) and in low-input cropping systems (Kuhlmann and Baumgärtel 1991).
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