Phosphorus (P) is a central element to life on Earth. Living organisms are dependent on a persistent supply of P as it is crucially involved in most major metabolic processes, e.g. in energy transfer as adenosine triphosphate (ATP). Likewise, plants rely on P to secure energy production in photosynthesis (Smil 2000, Ruttenberg 2009). Therefore, the fundamental significance of P in agriculture and food production is beyond question.In nature, we can identify several P pools (Smil 2000, Ruttenberg 2009). The largest P reservoir in the lithosphere occurs in marine and freshwater sediments (about 800-4000 × 10 6 Mt P). The entire phytomass (terrestrial and marine; about 570-625 Mt P) amounts to over 90% of P stored in the totality of all living organisms. Gaseous compounds of P are not stable; therefore, only an insignificant amount (0.028 Mt P) exists in the atmosphere as dust and sea spray picked up by wind erosion. The flows of P between these reservoirs are slow (one cycle may take more than 1 million years), which is caused by the low solubility of phosphate in water and the lack of an airborne reservoir.In soils, P derives mainly from weathering of the primary mineral apatite (Schlesinger 1997). The average total P in soils ranges from 200 mg/kg (in older/highly weathered soils) to 800 mg/kg (in younger/less developed soils) (Cross and ABSTRACTPhosphorus (P) fertilization is commonly based on soil testing, for which a variety of different soil P extraction methods are in use. The aim of this study was to compare 14 soil P extraction methods in terms of their extraction yield and their relation to soil properties. Fifty contrasting agricultural topsoils were sampled from Austria and Germany. The soils were extracted with the following methods/extractants: H 2 O, CaCl 2 , LiCl, Olsen, Bray and Kurtz II (Bray II), Mehlich 3, calcium-acetate-lactate (CAL), iron oxide impregnated filter papers (Fe-oxide P i ), cation and anion exchange membranes (CAEM), acid ammonium oxalate, citrate-bicarbonate-dithionite, HCl, organic P and total P. The extracted P varied over three orders of magnitude and increased in the order H 2 O < CaCl 2 < LiCl < Fe-oxide P i < Olsen < CAL < CAEM < Mehlich 3 < Bray II < dithionite < organic P < HCl < oxalate < total P. This sequence is in accordance with previous studies and reflects different extraction mechanisms and P pools. The different extraction methods were generally well correlated, especially when P extraction was achieved by a similar mechanism. The soil properties most influential on P extractability were pH, carbonate content, texture as well as iron oxide content and crystallinity. Our results show that the different extraction methods extract distinct pools of soil P with strongly varying extractability, and that the extractability of a given pool may be influenced by different soil properties to different extents. If and how these relationships translate to plant P uptake requires further examination.

A b s t r a c t. Agricultural intensification, especially enhanced mechanisation of soil management, can lead to the deterioration of soil structure and to compaction. A possible amelioration strategy is the application of (structural) lime. In this study, we tested the effect of two different liming materials, ie limestone (CaCO 3 ) and quicklime (CaO), on soil aggregate stability in a 3-month greenhouse pot experiment with three agricultural soils. The liming materials were applied in the form of pulverised additives at a rate of 2 000 kg ha -1 . Our results show a significant and instantaneous increase of stable aggregates after quicklime application whereas no effects were observed for limestone. Quicklime application seems to improve aggregate stability more efficiently in soils with high clay content and cation exchange capacity. In conclusion, quicklime application may be a feasible strategy for rapid improvement of aggregate stability of fine textured agricultural soils.

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The aim of this study was to test different soil phosphorus (P) extraction methods in relation to plant P uptake. A greenhouse pot experiment was conducted with spring wheat. The soils were extracted with the following methods/extractants: H₂O, CaCl₂, LiCl, iron oxide impregnated filter papers (Fe-oxide P_i), Olsen, calcium-acetate-lactate (CAL), cation and anion exchange membranes (CAEM), Mehlich 3, Bray and Kurtz II (Bray II), citrate-bicarbonate-dithionite, organic P, HCl, acid ammonium oxalate, total P. Plant P uptake was in the range of the P extracted by neutral salt solutions (CaCl₂, LiCl). P extracted with H₂O, CaCl₂ and CAEM correlated best with plant P uptake over one growing season, while several established soil P test methods, including CAL, Mehlich 3 and Bray II, did not show significant correlations. When grouping the soils according to pH, the weaker extraction methods (H₂O, CaCl₂, LiCl) showed significant correlations with plant P uptake only for the low and intermediate pH groups (pH in 1 mol/L KCl ≤ 6.6), while some of the stronger extraction methods (CAL, Mehlich 3, Bray II, dithionite, oxalate, total P) showed significant correlations only for the high pH group (&gt; 6.6) comprised of calcareous soils. It was concluded that weaker P extraction methods, especially neutral salt solutions best predict plant-available P in the short term. However, they do not perform well for calcareous (and clayey) soils and do not account for P that may become available beyond one growing season.