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Rayment G.,Australasian Soil and Plant Analysis Council
Communications in Soil Science and Plant Analysis | Year: 2013

Many diagnostic soil-testing services only use measures of extractable and/or exchangeable potassium (exchangeable K) to provide guidance on the need or otherwise for applications of K fertilizer. Less commonly, soil tests for nonexchangeable, plant-available K are included, although this combination of soil K tests does not unequivocally detect situations where soil total K reserves are critically low. This article provides examples of how atom ratios between measured values of total K and exchangeable K in soils can alert crop advisors and growers of such situations. Specifically, total K / exchangeable K ratios at different depths in samples (136 sites) from canelands of northeastern Australia and from cropping lands (67 samples) in Fiji were found to vary from around 1.0 to 1,235. Lowest total K / exchangeable K ratio values were commonly recorded in soils from the Bundaberg/Maryborough region of northeastern Australia and from highly weathered ferruginous latosols supporting "talasiga" vegetation in Vanua Levu, Fiji. The Vanua Levu soils contained much lower total K reserves than did cropping soils near Nadi on Viti Levu. Summary details of total K / exchangeable K ratios for the five cane-growing regions of northeastern Australia are provided, together with soil K data to 800-900 mm in selected soils from the Fijian Islands. There is need to seriously consider additions of plant-available K when levels of exchangeable K are at or below accepted "critical levels" and corresponding total K / exchangeable K ratios are around <2 to 3. Total K and exchangeable K in the soils tested were not intercorrelated. © 2013 Copyright Taylor & Francis Group, LLC.

Rayment G.E.,Australasian Soil and Plant Analysis Council | Hill R.,Australasian Soil and Plant Analysis Council | Hill R.,New Hill | Greaves A.,New Hill
Communications in Soil Science and Plant Analysis | Year: 2012

There is growing interest in the use of near-range and/or midrange infrared (IR) diffuse reflectance spectroscopy (NIR and MIR) as nondestructive alternatives to chemical testing of soils. This trend is supported by research on how best to correlate IR spectral data with results obtained by conventional laboratory measurements. While for soils there is growing interest in developing local and national calibrations using "legacy" data, the proven analytical performance of provider laboratories now and earlier, the moisture status of reported results, and the method of soil preparation warrant greater attention. Examples for soil carbon (C) and total soil nitrogen (N) from Australasian interlaboratory proficiency testing across multiple years from 1993 are provided to demonstrate the magnitude of past and present measurement uncertainties, including the effects of method and different concentrations. The evidence is sufficient to require those commissioned to develop NIR and MIR calibrations to subject their prototype calibrations to external peer review by participating in credible, independent interlaboratory proficiency testing programs for ≥12 months, including checks on soil moisture status and possible effects of sample preparation. To rate as credible for most uses, the prototype results should be within the interquartile range for each sample and ideally there should be no outliers and few stragglers. Across the period of assessment (1993-2008), users of Walkley and Black organic C and Kjeldahl digestion for total soil N (Kjeldahl method does not measure total N, but most of the organic N plus an undetermined proportion of nitrate and nitrate present in the sample; quantitative inclusion of both requires a modification of the Kjeldahl procedure) declined as use of furnace technologies for soil C and N increased linearly. There is a strong case to commission two or three well-performing and experienced laboratories to reanalyze samples in "legacy" soil collections prior to finalizing predictive relationships with NIR/MIR spectra for the same samples. © 2012 Copyright Taylor and Francis Group, LLC.

Rayment G.E.,Australasian Soil and Plant Analysis Council | Lyons D.J.,Australasian Soil and Plant Analysis Council
Communications in Soil Science and Plant Analysis | Year: 2012

The 1992 Australian Laboratory Handbook of Soil and Water Chemical Methods (the handbook) of Rayment and Higginson defines much of the contemporary soil chemical methodology used in Australia for soil fertility and land-resource survey assessments. In addition, codes from the handbook identify methodological details in Australian soil databases, while the codes summarize most tests used for certification purposes by the Australasian Soil and Plant Analysis Council (ASPAC) in its interlaboratory soil proficiency testing programs. A worthy, comprehensive replacement was required as the handbook is out of date in places and out of print. This article provides information on the handbook's replacement with a new book by Rayment and Lyons, titled Soil Chemical Methods-Australasia. Method codes and other strengths of the handbook have been retained and many new tests have been added. There are new chapters on acid sulfate soils, total miscellaneous elements, and miscellaneous extractable elements, plus inclusions and improvements throughout. Modern analytical techniques, such as flow-injection analysis, inductively coupled plasma-mass spectroscopy (ICP-MS), and potential alternatives to chemical testing offered by near-range and midrange infrared diffuse reflectance spectroscopy, are included. Examples of new additions include the Mehlich 3 "universal" soil test (and derived environmental P tests) and methods for potentially mineralizable nitrogen, labile carbon, particulate organic carbon, and charcoal. Around 200 methods are fully described, while information of measurement performance at different concentrations is provided where credible data were available from multiple, interlaboratory proficiency programs of ASPAC. Procedures for the chemical testing of water are no longer included, except where relevant to saturation extracts of soils. While there are informative and much expanded method preambles and reference lists, the new 2011 book has its focus on methodology. A scheme to agree on recommended methods for different soils and regional locations is outlined. © 2012 Copyright Taylor and Francis Group, LLC.

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