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Interlaboratory comparison programs have been found to be useful to investigate potential error sources and therefore to remove or minimize their effects. A proficiency test was performed for five soil micronutrients [boron (B), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] by forty-nine independent Brazilian laboratories on four duplicated soil samples. Extraction of B was performed by hot water, whereas Fe, Mn, Cu, and Zn were extracted by diethylenetriaminepentaacetic acid (DTPA). The objectives were to compare the performance of different statistical methods for assessing between-laboratory variability (reproducibility) and to quantify the variability within single laboratories (repeatability). The statistical methods employed to compare interlaboratory analytical results were (1) Agronomic Institute method (mean, standard deviation, coefficient of variation), (2) Z1score (mean and standard deviation, including outliers), (3) Z2score (mean and standard deviation, excluding outliers), (4) robust Z score (median and standardized interquartile amplitude) denoted as Z3, (5) Cochran test, and (6) Cochran + Grubbs tests. In addition, the robust Z-score method, denoted as Z4, was used to assess intralaboratory variability. The performance of any laboratory for the analysis of soil micronutrients varied depending on the statistical method applied. The percentage of laboratories providing satisfactory results was 79 percent (Agronomic Institute), 95 percent (Z1), 92 percent (Z2), 89 percent (robust Z3score), 97 percent (Cochran), and 95 percent (Cochran + Grubbs). The Z-score tests become stronger and more rigorous when outliers were excluded (Z2) or when the standardized interquartile amplitude was used (Z3). Cochran and Grubbs tests, which are based on the removal of extreme values, were weaker than the other tests evaluated. In conclusion, the method employed by the proficiency test of the Agronomic Institute for removing outliers has been found to be the strongest and strictest one, yielding a reliable comparison of the results from soil micronutrient analyses.Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lcss. [ABSTRACT FROM PUBLISHER]

The control of contaminants in fertilizers and industrial by-products is fundamental to safe food production, and it requires low-cost, reliable test methods. The aim of this study was to evaluate the performance of the USEPA 3051a and alternative analytical methods [concentrated hydrochloric acid (HCl), 10 percent HCl, 10 percent sulfuric acid (H2SO4), and 50 mmol L−1diethylenetriaminepentaacetic acid (DTPA)] for quantifying the levels of lead, cadmium, chromium, and nickel in zinc and/or copper sources. The sample digestions with concentrated HCl, H2SO4, and nitric acid (HNO3) (USEPA 3051a) were heated. Extraction without heating and stirring was employed in 10 percent HCl and 50 mmol L−1DTPA methods. The Graybill’s modified F-test, t-test for mean error, and the linear correlation coefficient analysis were used to compare test method performance. Equivalent results to USEPA 3051a were found with the following methods: DTPA for the extraction of lead in zinc sources and concentrated HCl and H2SO4for the extraction of cadmium and chromium in copper sources. However, the absolute values of cadmium, chromium, and nickel recovered by the use of H2SO4were greater regardless of the source. The greater extraction of contaminants in the evaluated methods suggests that there is need to review the official method if the aim is to quantify the total levels of these elements in raw materials and mineral fertilizers. [ABSTRACT FROM PUBLISHER]

Soils of the Brazilian Cerrado biome have been found to be deficient in copper (Cu) and zinc (Zn). In this area, an Oxisol was deeply excavated in 1962 during the construction of a hydroelectrical plant, and the exposed saprolite material was abandoned, without any reclamation measures. The abandoned land was a harsh environment for plant growth, and the secondary vegetation has not recovered. A field trial was established in 1992 to assess the effects of different grass species and lime amendments on soil reclamation at the degraded site. In 2011 soil samples were collected at three depths (0–10, 10–20, and 20–40 cm) from vegetated and bare plots over tilled saprolite, from an untreated area of the saprolite, and from an Oxisol under native forest, used as external reference. Nineteen years after the reclamation effort was begun, the organic carbon (OC) content of the restored saprolite still was much lower than that of the Oxisol under natural vegetation. The undisturbed Oxisol was deficient in extractable Cu (0.16–0.10 mg kg−1) and Zn (0.10–0.02 mg kg−1) and exhibited rather low concentrations of extractable iron (Fe; 5.24–1.47 mg kg−1) and manganese (Mn; 3.21–0.77 mg kg−1). However, the saprolite under reclamation showed even lower levels of these elements compared to the native forest soil. In the natural soil, OC, N, extractable Fe, Mn, and Cu showed stratification, but this was not the case for extractable Zn. Although the reclaimed saprolite still was far from predisturbance conditions, the revegetation treatments promoted recovery of OC, N, Fe, Mn, and Cu at the surface layers, which resulted in incipient stratification. Extractable Fe, Mn, and Cu were correlated to OC, whereas no association between Zn and OC was detected. Our results also suggest that reclamation of the excavated saprolite may be constrained by micronutrient deficiencies and mostly by the extremely low levels of Zn and Cu. [ABSTRACT FROM PUBLISHER]