Data/hora: 21/06/2024 19:02:54

Biblioteca(s): 	Embrapa Cerrados.	
Data corrente: 	16/07/1999	
Data da última atualização: 	16/07/1999	
Autoria: 	NEUFELDT, H.; SILVA, J. E. da; AYARZA, M. A.; ZECH, W.	
Título: 	Phosphorus fractions under different land-use systems in oxisols of the Brazilian cerrados.	
Ano de publicação: 	1999	
Fonte/Imprenta: 	In: THOMAS, R.; AYARZA, M.A., ed. Sustainable land management for the oxisols of the Latin American savannas: dynamics of soil organic matter and indicators of soil quality. Cali: CIAT, 1999.	
Páginas: 	p.146-158.	
Idioma: 	Inglês	
Conteúdo: 	We examined whole-soil samples and particle-size fractions to study the distribution of different phosphorus (P) fractions after land-use change from native savanna to crops, pastures, and reforestation on clayey and loamy Oxisols of the Brazilian savannas. Phosphorus was extracted sequentially, according to a modified hedley procedure, into inorganic and organic P (NaOH-extractable Pi and Po, respectively), and recalcitrant P (Phc1 and Pres). Under natural conditions of strong P deficiency, over 60% of NaOH-extractable P was organic, reflecting the high contribuint of Po to plant nutrition. Fertilization elevated inorganic Po. The increase of inorganic P forms from fertilizer P was greatest in the Pi and lowest in the Pres fractions. After fertilization, the reforested sites maintained high NaOH-extractable P through efficient recycling, whereas at the crop and pasture sites, P tended to accumulate in recalcitrant forms. Possibly, the adsorption of P to oxyhydroxides was reduced at the more acid reforested sites by complexation of Fe and Al oxides with organic acids. The ratio of NaOH-extractable Pi to Po appeared to effectively reflect the P status of the land-use systems and P deficiency increased in ascending order from native savanna > pasture > reforestation > crop, independently of soil type. The particle-size separates reflected P transformations along a biological and mineralogical gradient, which is discussed with respect to origin and distribution of natural and fertilizer P forms. That is, (1) P in particle-size separates was enriched in the clay and depleted in the sand fractions such that 70%-87% of total P was bound in the clay; (2) residual P increased relatively at the expense of HCl-extractable P with decreasing particle-size, indicating a continuously stronger adsorption to oxyhydroxides; (3) the proportions of organic P were generally lowest in the 20-50-um fraction because P in particulate organic matter was already depleted and transformed into microbially mediated Po, which was enriched in the clay and silt fractions; (4) fertilizer P accumulated in the 20-50-um fraction and was subsequently transferred to the silt and clay fractions but remained largely in inorganic form.	
Thesagro: 	Cerrado; Composto Orgânico; Fósforo; Fracionamento; Uso da Terra.	
Thesaurus Nal: 	fractionation; land use; organic compounds; phosphorus.	
Categoria do assunto: 	--	
Registro original: 	Embrapa Cerrados (CPAC)	
Exemplares: 	CPAC - (2462-1) - UPC - PL - -- - CRI4998 -  - CRI4998 - DIS