Phosphorus Availability for Plant Uptake in a Phosphorus‐Enriched Noncalcareous Sandy Soil

Mining soil phosphorus (i.e., harvesting P taken up from the soil by a crop grown without external P addition) has been proposed as a possible management strategy for P‐enriched soils to decrease the risk of P leaching. We performed a pot experiment in a greenhouse where grass was cropped on a P‐enriched noncalcareous sandy soil at zero P application over a period of 978 d. We determined the long‐term availability of soil P and evaluated the effectiveness of mining soil P to decrease P in different pools. There were two treatments: soil layers in the pots of either 5 or 10 cm thickness. Soils were analyzed at various stages of the experiment. Phosphorus in soil solution and the total pool of sorbed P were estimated using 1:10 (w/v) 0.01 M CaCl 2 extracts and acid ammonium oxalate (P ox ), respectively. A desorption isotherm was constructed, which described the relationship between P in soil solution and the total pool of sorbed P for the soils of the 5‐ and 10‐cm treatments. The Langmuir equation gave a very good description of the isotherm. In the long‐term, 65% of P ox in the initial soil can be removed by plant uptake, as was calculated from the Langmuir equation and a critical P concentration in soil solution at which P uptake can just be maintained. Thus, P ox may be largely plant available. From the strong nonlinearity of the desorption isotherm, it can be understood why the relative decrease of the P concentration in the CaCl 2 extracts was much larger than the relative decrease of P ox Mining soil P decreased the P concentration in soil solution effectively and, therefore, risk of P leaching from our P‐enriched soil.