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The phosphorus status of German cropland—An inventory of top‐ and subsoils (2020)

Gocke, M., Don, A., Heidkamp, A., Schneider, F., Amelung, W.

The phosphorus status of German cropland—An inventory of top‐ and subsoils, (),

doi:10.1002/jpln.202000127

Abstract

Background: In search for more sustainable crop production, the subsoil has recently come into focus as considerable reservoir of nutrients and water.

Aims: Dimensions of subsoil phosphorus (P) reserves are yet largely unknown but crucial for identifying regions suitable to include subsoil into sustainable management strategies.

Methods: We analyzed stocks of total and plant‐available (calcium acetate lactate‐extractable) P in 96 representative soil profiles of German arable land down to 1 m depth.

Results: We found that the German arable soils stored, on average, 8 t ha−1 of total P, of which nearly 500 kg ha−1 were readily plant‐available. Notably, one third of plant‐available P was located below the plow layer and one fifth even at depths below 0.5 m. The depth gradients of plant‐available P stocks were affected more by major reference soil group than by texture. Generally, Chernozem but also Anthrosol, Gleysol and Fluvisol exhibited the largest P stocks in German cropland. The contribution of plant‐available P to total P stocks was larger in sandy and extremely acidic (pH < 4.5) soils compared with more fine‐grained and slightly acidic to alkaline soils, possibly because fertilization compensated for overall lower total P stocks at these sites. Generally, the more P was stored in topsoils, the more P was stored also in subsoils.

Conclusions: A hypothetical crop utilization of 10% from plant‐available P stocks and 0.1% from total P stocks from shallow subsoil could compensate for P fertilization by ca. 8 kg ha−1, but the rate of plant‐available P replenishment in subsoil likely remains the crucial factor for the role of subsoil P stocks in crop nutrition. Generally, the large P reserves found in subsoil could act as an ‘insurance' system for crops.

Sustainable Subsoil Management