Abstract
Efficient analytical methods for the quantification of plant-available Zn contained in mineral fertilizers and industrial by-products are fundamental for the control and marketing of these inputs. In this sense, there are some doubts on the part of the scientific community as well as of the fertilizer production sector, whether the extractor requested by the government (Normative Instruction No. 28, called 2nd extractor), which is citric acid 2 % (2 % CA) (Brasil, 2007b), is effective in predicting the plant availability of Zn via mineral fertilizers and about the agronomic significance of the required minimal solubility of 60 % compared to the total content (HCl) (Brasil, 2007a). The purpose of this study was to evaluate the alternative extractors DTPA, EDTA, neutral ammonium citrate (NAC), buffer solution pH 6.0, 10 % HCl, 10 % sulfuric acid, 1 % acetic acid, water, and hot water to quantify the contents of Zn available for maize and compare them with indices of agronomic efficiency of fertilizers and industrial by-products when applied to dystrophic Clayey Red Latosol and Dystrophic Alic Red Yellow Latosol with medium texture. The rate of Zn applied to the soil was 5 mg kg-1, using the sources zinc sulfate, commercial granular zinc, ash and galvanic sludge, ash and two brass slags. Most Zn was extracted from the sources by DTPA, 10 % HCl, NAC, 1% acetic acid, and 10 % sulfuric acid. Recovery by the extractors 2 % CA, EDTA, water, and hot water was low. The agronomic efficiency index was found to be high when using galvanic sludge (238 %) and commercial granular zinc (142 %) and lower with brass slag I and II (67 and 27 %, respectively). The sources galvanizing ash and brass ash showed solubility lower than 60 % in 2 % CA, despite agronomic efficiency indices of 78 and 125 %, respectively. The low agronomic efficiency index of industrial by-products such as brass slag I and galvanizing ash can be compensated by higher doses, provided there is no restriction, as well as for all other sources, in terms of contaminant levels of arsenic, cadmium, chromium, lead, and mercury as required by law (Normative Instruction No 27/2006). The implementation of 2nd extractor 2 % CA and the requirement of minimum solubility for industrial by-products could restrict the use of alternative sources as potential Zn sources for plants.
Highlights
After technological innovation in agriculture has boosted crop yields, any further advance will depend increasingly on improving the factors of production efficiency
(1) Part of the dissertation of the first author submitted to the Agronomic Institute of Campinas (IAC)
MATERIAL AND METHODS The study was divided into two phases: phase I consisted of a qualitative characterization of the main minerals present in the samples by X-ray diffraction, performed at the Institute of Biological Sciences and the Federal University of Ouro Preto/MG, and the quantification of the Zn levels soluble in the 2nd extractor and of the total content in HCl; both analyses were performed at the soil science center of the Agronomic Institute of Campinas (IAC), in Campinas, São Paulo
Summary
After technological innovation in agriculture has boosted crop yields, any further advance will depend increasingly on improving the factors of production efficiency. One example is the application of micronutrients to the soil, becoming increasingly relevant in the agricultural sector of Brazil. A 13-fold increase was reported for the consumption of such inputs from 1990 to 2003, whereas grain yield increased by 112 % in this period (Yamada, 2004). In 20 % of 7,816 soil samples of the State of São Paulo and in 33 % of 5,614 soil samples from other States, extracted by DTPA at pH 7.3 (Abreu et al, 2005), the Zn content was considered low (< 0.5 mg dm-3) (Raij et al, 2001). The application of Zn-containing fertilizers is becoming increasingly important for a number of different crops
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