Desgaste dos extratores Mehlich-1 e Fosfato Monocálcico e fatores que controlam a solubilização do fosfato de Bayóvar

• Ano de defesa: 2014
• Autor(a) principal: Novais, Sarah Vieira
• Orientador(a): Mattiello, Edson Marcio
• Banca de defesa: Assis, Igor Rodrigues de , Leite, Roberto de Aquino
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Solos e Nutrição de Plantas
• Departamento: Fertilidade do solo e nutrição de plantas; Gênese, Morfologia e Classificação, Mineralogia, Química,
• País: BR
• Palavras-chave em Português: Química do solo; Solos - Teor de fosforo; Fosfato de Bayóar
• Palavras-chave em Inglês: Chemistry of soil; Soil - Content of phosphorus; Phosphate Bayóar
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO
• Link de acesso: http://locus.ufv.br/handle/123456789/5538

The low availability of phosphorus (P) in tropical soils makes it one of the most studied plant nutrients in the world. Phosphorus fertilization is essential for economically satisfactory yields and the assessment of its long-term availability has become indispensable for the management of this nutrient in agricultural systems. This study was based on two experiments: experiment I, to evaluate the wear of Mehlich-1 (M-1), used in routine analyses of soil available P, and the resulting changes in the currently used critical P levels. For comparison, extractor wear of available sulfur (S) was tested in the same way, using the same soil samples. Twenty soil samples were selected to cover the range of remaining P (P-rem) from 0 to 60 mg L-1 P, as a measure of the phosphate buffering capacity (PBC) in the soil. The extractors M-1 and monocalcium phosphate in acetic acid (MCPa) were routinely applied to determine P and S, respectively, according to protocols used in the Department of Soil Science, Federal University of Viçosa. The pH variation of the two extractors, SO42- of M-1 and of H2PO4- of MCPa, was determined in the soil extract after a rest period of 16 h. A slight but significant wear of acidity (increase in pH) occurred with increasing PBC (decrease in P-rem). On the other hand, SO42- of M -1 was exhausted with increasing PBC, according to a linear-plateau model. This fact indicates the need to adopt an equally discontinuous model for the interpretation of P-available soil with different values of P-rem or PBC. On the other hand, S extractor wear was continuous, linear, with decreased P-rem or increased PBC, which proves that the currently adopted relationship between available S and PBC is correct. For experiment II, samples of Bayovar Rock Phosphate (RP) in an aqueous suspension were placed in a dialysis cassette (Slide-A-Lyzer Dialysis Cassette G2) and this in a 200 mL beaker with 150 mL of an aqueous suspension with drains of P and/or Ca:anionic resin (AR), cationic resin (CR), mixed resin (MR), goethite (Goe), Goe+AR, Goe + RC, and a control treatment (only natural RP). The pH of all treatments was adjusted to 4.5 or 6.0, in five replications. These treatments were stirred for 12 h daily for 18 days, in a horizontal shaker at 130 opm, and then left to stand until completing 30 days of equilibrium due to mechanical deterioration (breaking) of the membranes. In each treatment, solution P, labile P residual P, and total P (the sum of the previous and fractions) were determined. Goethite as P drain caused greater RP solubilization than the other drains at pH 4.5 and than the other drains containing no additional AR or RC. Similarly, AR (P drain) caused similar solubilization to that of RC (Ca drain), indicating that the P drain was as effective in solubilizing RP as the Ca drain. The presence of AR and RC strongly inhibited the action of Goe at pH 4.5, as solubilizing agent of RP. The higher solubilization generally caused by Goe resulted in lower levels of labile P. The effect of higher acidity solubilizing RP was generally less effective than that of the separate or combined drains.