Browsing by Autor "Simon D. Speirs"

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Making Better Fertiliser Decisions for Cropping Systems in Australia: an overview
(CSIRO Publishing, 2013) Simon D. Speirs; D. J. Reuter; K. I. Peverill; Ross Brennan
Australian grain production depends on applied fertiliser, particularly nitrogen (N) and phosphorus (P), and to a lesser extent potassium (K) and sulfur (S). Despite this dependence, soil testing is used sparingly as a tool to underpin fertiliser decisions. Some grain producers typically conduct soil tests at least once every 3 years on a selection of individual fields, but it is broadly understood that many grain producers use soil testing rarely or not at all. The choice by many grain producers not to support fertiliser decisions by soil testing relates to several factors. One key factor has been a perception that soil test interpretation criteria, previously published separately before collation by K. I. Peverill, L. A. Sparrow, and D. J. Reuter, may be biased or unreliable. The current paper provides an overview of research findings, presented in this special edition of Crop & Pasture Science, describing a national approach to the collation of all available and statistically valid N, P, K, and S response trials for cereal, oilseed, and pulse crops in Australia. It provides an overview of the process adopted to make this single national dataset available to both the grains and fertiliser industries. The process to build adoption has formed an integral component of the approach, as calibration data derived from the national database are being used to underpin soil test interpretation as part of fertiliser recommendations made through Fertcare to grain producers in Australia.
Soil phosphorus tests II: A comparison of soil test–crop response relationships for different soil tests and wheat
(CSIRO Publishing, 2013) Simon D. Speirs; Brendan Scott; P. W. Moody; Sean Mason
The performance of a wide range of soil phosphorus (P) testing methods that included established (Colwell-P, Olsen-P, BSES-P, and CaCl2-P) and more recently introduced methods (DGT-P and Mehlich 3-P) was evaluated on 164 archived soil samples corresponding to P fertiliser response experiments with wheat (Triticum aestivum) conducted in south-eastern Australia between 1968 and 2008. Soil test calibration relationships were developed for relative grain yield v. soil test using (i) all soils, (ii) Calcarosols, and (iii) all ‘soils other than Calcarosols’. Colwell-P and DGT-P calibration relationships were also derived for Calcarosols and Vertosols containing measureable CaCO3. The effect of soil P buffer capacity (measured as the single-point P buffer index corrected for Colwell-P, PBICol) on critical Colwell-P values was assessed by segregating field sites based on their PBICol class: very very low (15–35), very low (36–70), low (71–140), and moderate (141–280). All soil P tests, except Mehlich 3-P, showed moderate correlations with relative grain yield (R-value =0.43, P &lt; 0.001) and DGT-P exhibited the largest R-value (0.55). Where soil test calibrations were derived for Calcarosols, Colwell-P had the smallest R-value (0.36), whereas DGT-P had an R-value of 0.66. For ‘soils other than Calcarosols’, R-values &gt;0.45 decreased in the order: DGT-P (r = 0.55), Colwell-P (r = 0.49), CaCl2-P (r = 0.48), and BSES-P (r = 0.46). These results support the potential of DGT-P as a predictive soil P test, but indicate that Mehlich 3-P has little predictive use in these soils. Colwell-P had tighter critical confidence intervals than any other soil test for all calibrations except for soils classified as Calcarosols. Critical Colwell-P values, and confidence intervals, for the very very low, very low, and low P buffer capacity categories were within the range of other published data that indicate critical Colwell-P value increases as PBICol increases. Colwell-P is the current benchmark soil P test used in Australia and for the field trials in this study. With the exception of Calcarosols, no alternative soil P testing method was shown to provide a statistically superior prediction of response by wheat. Although having slightly lower R-values (i.e. &lt;0.1 difference) for some calibration relationships, Colwell-P yielded tighter confidence intervals than did any of the other soil tests. The apparent advantage of DGT-P over Colwell-P on soils classified as Calcarosols was not due to the effects of calcium carbonate content of the analysed surface soils.