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An Examination of Spin–Lattice Relaxation Times for Analysis of Soil and Manure Extracts by Liquid State Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy

^a AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, Otago, New Zealand
^b Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
^c Department of Geological and Environmental Science, Stanford University, Building 320, Room 118, Stanford, CA 94305-2115

View larger version (16K): [in a new window]   Fig. 1. Phosphorus-31 nuclear magnetic resonance (NMR) spectra of each reconstituted soil and manure sample at the longest employed. The term S/N is the signal to noise ratio. Regions within a spectrum for P compound classes are given for the Oamaru soil.

View larger version (11K): [in a new window]   Fig. 2. Inversion recovery stacked spectra of the Taupo NaOH-EDTA reconstituted soil extract. The numbers at the base of each spectrum indicate the delay time used.

View larger version (17K): [in a new window]   Fig. 3. Phosphorus-31 nuclear magnetic resonance (NMR) spectra of the Stewart and Taupo soil extracts using a delay of 0.1 and 5 s. The term S/N is the signal to noise ratio. Assignments are given for each class of P compound above their respective peak. Numbers refer to concentrations given in Table 4.

View larger version (20K): [in a new window]   Fig. 4. Phosphorus-31 nuclear magnetic resonance (NMR) spectra of the sheep dung extract using a delay of 0.1 and 15 s. The term S/N is the signal to noise ratio. Assignments are given for each class of P compound above their respective peak. Numbers refer to concentrations given in Table 4. The miniature spectra show the full intensity of orthophosphate relative to other peaks.

View larger version (14K): [in a new window]   Fig. 5. Relationship between the concentration of Fe in the reconstituted sample and spin–lattice relaxation rate (T1) for orthophosphate. Manure samples are plotted with white fill.

View larger version (27K): [in a new window]   Fig. 6. Linear regressions between spin–lattice relaxation rate (T1) values for orthophosphate (solid line) or orthophosphate monoesters (from the four peaks representing largely inositol hexakisphosphate), orthophosphate diesters, and pyrophosphate (dashed line), and the ratio of P to Fe and Mn in each reconstituted nuclear magnetic resonance (NMR) sample (on a mg L–1 basis). Note, the 95% confidence intervals for each relationship are given as the dotted lines and the number of asterisks denote significance at the 0.01 (**) and 0.001 (***) probability levels. Data from Cade-Menun et al. (2002) are included as solid black symbols. Manure samples are plotted with white fill.