Disponibilidade de fósforo em solo alcalino carbonático com uso de enxofre elementar

• Autor(a) principal: Abrantes, Ewerton Gonçalves de
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/123456789/29878
• topic: solos de reação alcalina; fixação de P; fracionamento de P; extratores de P; oxidação de S; CNPQ::CIENCIAS AGRARIAS

Alkaline carbonate soils have low availability of phosphorus (P), due to the presence and sorption, in calcium carbonates, of different forms of calcium phosphates. Thus, increasing the availability of P in these soils involves reducing the pH and increasing the solubility of precipitated phosphates, which can be achieved with the use of elemental sulfur (So). For these reasons, the objective of this work was: a) to evaluate the influence of So on soil reaction and on the dynamics of inorganic fractions of P; b) to evaluate the performance of different chemical extractors in the evaluation of available P in carbonate alkaline reaction soil in the northeastern semiarid region.The study consisted of two experiments, conducted in a protected environment, using material from the surface layer (0 - 0.30 m) of a Vertisol Haplic orthic hypocarbonate, collected in the municipality of Governador Dix-Sept Rosado, State of Rio Grande do Norte. In the first experiment, a completely randomized design with four replications was used, with treatments arranged in a 5 × 5 factorial, referring to five So rates (0; 50; 100; 150 and 200% of the dose of So to neutralize CaCO3, which was equivalent to 0; 15; 30; 45 and 60 g kg-1 of So), and five incubation times (T) (14; 28; 42; 56 and 70 days). The experimental unit consisted of a pot containing 0.3 kg of soil, with humidity maintained at 70% of field capacity. At the respective incubation times, soil samples were collected, dried and determined pH values in water, sulfate and CaCO3 contents, in addition to P-rem values; additionally, the P contents were determined by the extractors water (P-w), calcium chloride (P-CaCl2), Mehlich-1 (P-M1), Olsen (P-Olsen) and ion exchange resin (PIER). In the second experiment, a randomized block design with four replications was adopted, with treatments arranged in a 2 × 5 factorial, referring to two rates of So (0 and 30 g kg-1) and five rates of P [0; 25; 50; 75 and 100% of the CMAP value (889 mg kg-1 of P), which was equivalent to P rates of 0; 222.3; 444; 666.7 and 889 mg kg- 1]. Initially, pots containing 3 dm3 of soil were incubated with So rates for 42 days; then, P rates were applied, in the form of KH2PO4, and incubated again for 21 days. After this period, soil subsamples were collected from each pot and pH values in H2O, S-SO 2- contents and P contents by the extractors P-H O, P-CaCl , P-M1, POlsen and P–RTI were determined; additionally, the sequential fractionation of inorganic P was carried out, determining the fractions P-soluble, and P bound to aluminum (P-Al), iron (P-Fe) and calcium (P-Ca). Subsequently, two forage sorghum plants, cv. Ponta Negra. After 50 days of cultivation, the aerial part of the plants was cut, obtaining after drying the aerial part dry matter mass values (DMMV); in these samples, the P and S contents were determined and, subsequently, the accumulation of P and S in the aerial part was calculated. In the incubation assay, there was a decrease in pH with increasing So rates and incubation time, registering a reduction from 8.5 to 5.1 with a S0 rate of 60 g kg-1 incubated for 70 days. Elemental sulfur increased sulfate contents and P-rem values, but did not influence carbonate contents; moreover, it increased P-CaCl2 and PM-1 contents, reduced PIER and did not influence P-H2O and P-Olsen. The P-Olsen and P-IER levels do not correlate with variables that reflect the buffering capacity factor. In the correlation assay, the presence of So did not influence the DMMV, but increased the levels and accumulations of P and S. The extractors P-H2O, P-CaCl2, P-M1, P-Olsen and P-IER were highly correlated among themselves, in the presence and absence of So, but only the P-Olsen and P-RTI extractors correlated with the P accumulated by theplant. The P contents obtained by the P-Olsen and P-IER extractors were preferentially correlated with the P-Al fraction; however, the plant absorbed P in the following decreasing order: P-Ca > P-Fe > P-Al > P-H2O in the absence and P-Ca > P-Al > P-Fe > P-H2O in the presence of So. It was concluded that the P-Olsen and PIER extractors are the most suitable for the evaluation of available P in these soils.