Resumo

SUBERO, Neudis; RAMIREZ, Ricardo; SEQUERA, Omaira  e  PARRA, Julio. Fractions of soil phosphorus under long term rice culture. I. Inorganic phosphorus. Bioagro [online]. 2016, vol.28, n.1, pp.013-020. ISSN 1316-3361.

Soils cultivated with rice in the irrigation system of Guárico State, Venezuela, have been fertilized with phosphates for many years. The current state of knowledge of the forms of phosphorus in soils and their transformations into different fractions could lead to better diagnostic methods currently in use. Composite soil samples were collected from 0 to 20 cm deep in 43 farmer’s plots and the inorganic fractions (Pi) were determined in the laboratory. The Pi resin and Pi labile (both fractions considered available) represented only 2.7 to 5.5 % of total Pi (PiT), thus representing just a small portion of the P applied to the soil, whereas the moderately labile and slightly labile Pi were 7.1 to 9.3 times higher than the available fractions and showed a tendency to decrease with time. The unavailable forms were the most abundant (64.2 to 72.8 % of PiT). The occluded and recalcitrant Pi fractions increased with soil pH.

Palavras-chave : Available phosphorus; labile phosphorus; resin phosphorus.

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