Background: The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. Scope: We asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research. Conclusions: We identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems

Volcanic ash derived soils represent between 50-60% of the total arable land area of southern of Chile, and they are the most important soils for pasture production. In these soils, high phosphorus (P) fixation and, in turn, low P availability and high aluminium (Al) soluble concentrations (at low pH) are the most limiting factors for pasture production. At the same time, the complexes between Al-or iron-(Fe) and organic matter as well as short-range order alumino-silicates (allophane) allow the retention of huge quantities of soil P. The aim of this work was to assess the status of P by both sequential extraction procedure (Hedley) and 31 P-NMR analysis as influenced by Al and Fe in volcanic grasslands Andisols (Pemehue, Gorbea, Piedras Negras and Llastuco Soil Series) from Southern Chile. We applied Hedley chemical sequential fractionation to soils in order to examine the potential differences in extractable soil inorganic P (P i ) and organic P (P o ) fractions. We also determined total P and Olsen P in these grassland Andisols. Oxalate and pyrophosphate were employed to determine the active and organic matter complexed Al and Fe, respectively. Furthermore, we quantified Al and Fe in extracts of the Hedley P fractions. We found that Al extracted in oxalate was correlated positively with labile P o concentration, specifically with both the NaHCO 3 -P o (r=0.45, P≤0.01), and the NaOH-P o (r=0.43, P≤0.01) fractions. This observation was reinforced by 31 P-NMR analysis that showed higher monoester P and myo-IP 6 content in soils with higher amounts of oxalate Al. Hedley sequential fractionation procedure confirmed the role of Al in the NaOH-P o fraction for promoting P o storage, as both fractions were correlated (r=0.33, P≤0.05). In addition, Fe plays a substantial role in recalcitrant P accumulation as we found a high correlation between residual P and oxalate Fe (r=0.55, P≤0.01).

Andisols are characterized by a high phosphorus (P) fixation capacity, which is a limiting factor for plant production. Continuous application of P fertilizer may result in an accumulation of P associated with soil organic matter (SOM), which further acts to reduce the availability of the added P. The objectives of this study were (1) to evaluate the impact of P fertilizer inputs on the quantities and chemical forms of P, and (2) to investigate relationships between P forms SOM and land use. Topsoil (0-20 cm) and subsoil (20-40 cm) samples were taken from two Andisols series under grassland and arable cropping. Soil P forms were determined using sequential fractionation, while SOM analysis involved a combination of 13 C nuclear magnetic resonance (NMR) spectroscopy and pyrolysis-GC-mass spectrometry. Fertilization increased total P, total organic P, organic carbon, and inorganic P fractions, mainly in arable soils. Labile P was higher in grassland (3% of total P) than in arable soils (1% of total P). A clear effect of fertilization was observed on organic matter compounds measured by pyrolysis in both soil depths. Interestingly, the polysaccharide-derived compounds increased in fertilized soils and lipidderived compounds decreased. Thus fertilization principally affected labile P and labile SOM forms, whereas recalcitrant forms of P and SOM remained unchanged.

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