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DIVISION S-4—SOIL FERTILITY & PLANT NUTRITION

Phosphorus Dynamics in a Highly Weathered Soil as Revealed by Isotopic Labeling Techniques

^a Univ. of Adelaide, Soil and Land Systems, Glen Osmond, SA 5064, Australia
^b Inst. of Plant Sciences, Swiss Federal Inst. of Technology Zurich (ETH), Eschikon 33, CH-8315 Lindau, Switzerland
^c Berea College, CPO 2064, Berea, KY 40404, USA

^* Corresponding author (astrid.oberson{at}ipw.agrl.ethz.ch)

Isotopic labeling techniques have the potential to elucidate soil P dynamics and the fate of P sources added to the soil, but they have rarely been applied to highly weathered tropical soils. We collected soils from two crop rotations [continuous maize (COM; Zea mays L.) and maize-crotalaria (MCF; Crotalaria grahamiana Wight & Arn.) fallow rotation] in a field experiment in Kenya and incubated them for 9 wk after addition of a plant residue or inorganic phosphorus (P_i), both labeled with ³³P and added at 6 mg P kg^–1 soil, or after carrier-free labeling of isotopically exchangeable soil phosphorus (soil IEP). The amount of P and recovery of ³³P were determined in resin-extractable P_i (P_resin), microbial P (P_hex), and in a 0.1 M NaOH extract of samples from which P_resin and P_hex had been removed. The P_resin increased after addition of P_i, while P_hex increased after plant residue amendment, involving considerable microbial uptake of soil P. The recovery of ³³P in P_resin followed the order added P_i > soil IEP > plant residue, and decreased steadily from 7 to 22% after 1 d to 3 to 5% after 9 wk. The recovery of ³³P in P_hex remained constant throughout the incubation, being greater after plant residue amendment (15%) than in the other two treatments (4–7%). An additional 66 to 76% of ³³P was recovered in the NaOH extract, as much as 27% of which was in organic phosphorus (P_o) after plant residue amendment and 2 to 8% in the other two treatments. Similar to P dynamics after plant residue amendment, the comparison of the two rotations indicated a shift toward P_hex and P_o with increasing microbial activity due to previous fallow biomass incorporation.

Abbreviations: COM, continuous maize • ddH₂O, double-distilled water • MCF, maize-crotalaria fallow rotation • NaOH-P_i, inorganic phosphorus extracted with 0.1 M NaOH • NaOH-P_o, organic phosphorus extracted with 0.1 M NaOH • NaOH-P_resin, phosphorus of 0.1 M NaOH extracts recovered on resin membranes • NaOH-P_t, total phosphorus extracted with 0.1 M NaOH • P_fum, phosphorus extracted with resin membranes in the presence of hexanol • P_hex, hexanol-labile microbial phosphorus (difference between P_fum and P_resin corrected for sorption of microbial P) • P_i, inorganic phosphorus • P_o, organic phosphorus • P_resin, inorganic phosphorus extractable with anion-exchange resin membranes • P_t, total P • SA, specific activity • soil IEP, isotopically exchangeable soil phosphorus

This article has been cited by other articles:

				T. M. McBeath, E. Lombi, M. J. McLaughlin, and E. K. Bunemann Isotopic Exchangeability, Hydrolysis and Mobilization Reactions of Pyrophosphate in Soil Soil Sci. Soc. Am. J., September 1, 2008; 72(5): 1337 - 1343. [Abstract] [Full Text] [PDF]