Sorção e dessorção competitiva de fósforo e citrato em solos de textura muito argilosa e média

• Autor(a) principal: Souza, Matheus Fonseca de
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5504
• topic: Fósforo; Citrato; Solos; Phosphorus; Citrate; Soils; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

Phosphorus (P) is one of the nutrients that often limit plant growth, mainly in highly weathered soils, such as Oxisols. However, low molecular weight organic acids can reduce P sorption in these soils. The aim of the study was to evaluate the P and citrate competitive sorption in clayey and sandy loamy soils using a stirred-flow system. Experiments were performed with soil samples (0-20 cm layer) from clayey (RYL_clay) and sandy loam (RYL_sand_loam) Red-Yellow Latosols (Oxisols). In the first study citrate effect on the P sorption was evaluated. Treatments were set up according to a 2 x 5 factorial, with two soils types and five forms of P application (only P, P and citrate, and citrate addition 7, 22, 52 min before P addition), three replicates in a completely randomized block design. The highest P sorption in the RYL_clay and RYL_sand_loam corresponding to 44.1 e 25.2 % of P added, respectively, was found with no citrate application. In the presence of citrate, P sorption was lower for all treatments evaluated. Citrate and P together reduced the sorption of P initially added to 25.8 % in RYL_clay and 16.7 % in RYL_sand_loam, in comparison to P application only. In the second assay was evaluated the P application effect on the citrate sorption. Treatments were defined according to a 2 x 2 factorial, with two soils two forms of P and citrate application (only citrate, citrate and P) in three replications in randomized blocks. The highest citrate sorption in RYL_clay and RYL_sand_loam occurred when there was no P application, corresponding to 32.0 and 30.2 % of citrate applied, respectively. With P application citrate sorption was reduced to 26.4 and 19.7 % of citrate initially added in RYL_clay and RYL_sand_loam, respectively. In the study assay it was evaluated the kinetics of desorption of previously adsorbed as affected by citrate addition. Each soil received a P dose (RYL_clay = 0.545 mg g-1 and RYL_sand_loam = 0.2 mg g-1) corresponding to 50 % of P sorption maximum capacity (PSMC) and they were incubated for 0, 6, 24, 240, 480 and 960 h before evaluating the kinetics of P desorption. Treatments were defined according to a 2 x 2 x 6 factorial scheme, with two soils, two extractors (citrate and water) and six incubation times. The P viiidesorption was greater when citrate was use as extractor. P desorption with citrate and water was initially higher (up to 24 h incubation of P) in the RYL_clay and RYL_sand_loam, consisting in an initially rapid phase, followed by a slow release phase, suggesting that depending on the time of contact of P with the soil colloids the previously adsorbed P may be released to the soil solution if effectively competing ligands such as citrates are present.