An assessment of various measures of soil phosphorus and the net accumulation of phosphorus in fertilized soils under pasture
Date
2015
Authors
Mclaren, T.
Simpson, R.
Mclaughlin, M.
Smernik, R.
Mcbeath, T.
Guppy, C.
Richardson, A.
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Journal of Plant Nutrition and Soil Science, 2015; 178(4):543-554
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Timothy I. McLaren, Richard J. Simpson, Michael J. McLaughlin, Ronald J. Smernik, Therese M. McBeath, Christopher N. Guppy, and Alan E. Richardson
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Abstract
Phosphorus fertilizer use efficiency of pastures is often low because P accumulates in soils as sparingly-available forms of inorganic and organic P. The aim of this study was to use sequential chemical fractionation to identify which forms of P have accumulated in soil under permanent pasture from a medium-term (13 y) field experiment. Treatments included an unfertilized pasture (P0), and treatments designed to maintain soil P fertility at near ‘optimum’ (P1) and ‘supra-optimum’ (P2) levels for pasture growth; all levels of soil P fertility were continuously grazed with either a moderate or high stocking rate (SR09 and SR18). Summed concentrations of extractable inorganic and organic P, and residual P (i.e., non-extractable P) accounted for 20, 31, and 49% of total soil P (as determined by laboratory X-ray fluorescence), respectively, across all surface (0–10 cm) and subsurface (10–20 cm) soil layers. A large proportion of extractable inorganic and organic P was contained in the NaHCO3 and NaOH soluble fractions across all surface soil layers, and these fractions were also the most important sinks for fertilizer P. The accumulation of organic P appeared to plateau with increasing fertilizer addition, whereas inorganic P continued to increase. The majority of the P that had been applied as fertilizer (70%) was recovered in the surface soil layer (0–10 cm). Approx. 31 and 30% of the added P was recovered in the summed concentrations of extractable inorganic and organic P, respectively, of the surface soil layer at the optimum (P1) agronomic level of soil P fertility.
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© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim