Alternative copper (Cu) sources could be used in fertilizer production, although the bioavailability of copper in these materials is unknown. The objective of this study was to evaluate the extractants neutral ammonium citrate (NAC), 2 % citric acid, 1 % acetic acid, 10 % HCl, 10 % H 2 SO 4 , buffer solution pH 6.0, DTPA, EDTA, water, and hot water in the quantification of available Cu content in several sources, relating them to the relative agronomic efficiency (RAE) of wheat grown in a clayey Latossolo Vermelho eutrófico (Oxisol) and Neossolo Quartzarênico (Typic Quartzipsamment). Copper was applied at the rate of 1.5 mg kg -1 as scrap slag, brass slag, Cu ore, granulated copper, and copper sulfate. The extractants 10 % HCl, 10 % H 2 SO 4 , and NAC extracted higher Cu concentrations. The RAE values of brass slag and Cu ore were similar to or higher than those of Cu sulfate and granulated Cu. Solubility in the 2 nd NAC extractant, officially required for mineral fertilizers with Cu, was lower than 60 % for the scrap slag, Cu ore, and granulated copper sources. This fact indicates that adoption of the NAC extractant may be ineffective for industrial by-products, although no extractant was more efficient in predicting Cu availability for wheat fertilized with the Cu sources tested.

Ten P fertilizers were collected (commercial fertilizers) or synthesized (experimental sources) in order to obtain single superphosphates varying in water and citrate solubility. A standard source of P was also produced by crystallization of the water-soluble fraction of a triple superphosphate. Eleven P sources were band applied to a medium textured Xanthic Hapludox, in Bahia, Brazil (low content of resin-extractable P) at a rate of 80 kg ha -1 of NAC + H 2 O (neutral ammonium citrate plus water) soluble P 2 O 5 , with soybean as the crop which was grown to maturity. A check plot (control) was included in the study. Three of the P sources [single superphosphate produced from Araxa phosphate rock (PR), low-grade single superphosphate produced from Lagamar PR and the standard source of P] were also applied at rates to provide 40 and 120 kg ha -1 of NAC + H 2 O soluble P 2 O 5 . Yield of soybean was evaluated by analysis of variance with mean comparison performed utilizing LSD lines, considering the P sources applied at a rate of 80 kg ha -1 of P 2 O 5 + control. Regression procedures were used to study the relation between yield of soybean and rates of P 2 O 5 . The fertilizers tested performed equally well as a source of P for soybean. The level of water-soluble P did not influence fertilizer performance. Key words: acidulated phosphates, available P, phosphorus sources, water-insoluble P AVALIAÇÃO AGRONÔMICA DO FÓSFORO SOLÚVEL EM ÁGUA OU CITRATO DE FOSFATOS DE ROCHA ACIDULADOS PARA A SOJARESUMO: Dez fontes de P foram coletadas em unidades revendedoras de fertilizantes comerciais ou produzidas em laboratório de tal forma a obter superfosfatos simples com variabilidade em água e citrato neutro de amônio + água (CNA + H 2 O). Utilizou-se como fonte padrão de fósforo a fração solubilizada, filtrada e cristalizada de um superfosfato triplo. As onze fontes de P foram aplicadas nas linhas de semeadura de soja de um Xanthic Hapludox textura média, localizado no Município de Barreiras, Bahia (baixo teor de fósforo resina) na dose de 80 kg ha -1 de P 2 O 5 solúvel em CNA + H 2 O. Três das fontes (superfosfatos simples produzido a partir da rocha fosfática de Araxá e Lagamar e a fonte padrão) foram aplicadas também em doses de 40 e 120 kg ha -1 e uma parcela testemunha, sem P, adicionada ao experimento. A produtividade da soja foi avaliada por meio de análise de variância e comparação de médias, considerando-se as fontes de P aplicadas na dose de 80 kg ha -1 P 2 O 5 + parcela testemunha. Regressões foram utilizadas para estudar a relação entre a produtividade de soja e as doses de P 2 O 5 . Os fertilizantes tiveram igual comportamento como fonte de P às plantas de soja. O teor de P 2 O 5 solúvel em água não influenciou o comportamento dos fertilizantes. Palavras-chave: fosfatos acidulados, P disponível, fontes de fósforo, fósforo insolúvel em água

USEPA 3051a) were heated. Extraction without heating and stirring was employed in 10 percent HCl and 50 mmol L −1 DTPA 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 H 2 SO 4 for the extraction of cadmium and chromium in copper sources. However, the absolute values of cadmium, chromium, and nickel recovered by the use of H 2 SO 4 were 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.