Aluminum hydroxy-interlayered minerals and chemical properties of a subtropical Brazilian Oxisol under no-tillage and conventional tillage

Abstract

No tillage systems significantly influence the soil system, but knowledge about the effects on the mineralogy of tropical and subtropical soils is limited. This study evaluated the long-term effects (26 years) of no-tillage (NT) on aluminum hydroxy-interlayered minerals of a subtropical Oxisol in Southern Brazil (Guarapuava, PR), compared to the same soil under conventional tillage (CT). The clay fraction (< 2 μm) in soil samples of the surface horizons of a field experiment under both management systems was analyzed by X-ray diffraction (XRD) to identify and characterize Al hydroxy-interlayered minerals before and after treatment with sodium citrate to remove intra-layer material. Soil liquid (solution) and solid phases were also characterized. The contents of total organic C, exchangeable cations, P, and the values of extractable acidity and cation exchange capacity as well as electrical conductivity and levels of dissolved organic C, basic cations, aluminum, Si, and sulfur in the soil solution were higher in the NT soil. Under both soil management systems, more than 90 % of the total soluble Al was complexed with organic compounds, with similar Al activity. No significant changes were detected by 2:1 clay mineral XRD analyses in terms of extension or intercalation of Al-hydroxy-polymers in the no-tilled in comparison to the conventionally tilled soil. In both soil management systems, Al and Si activities in the soil solution indicated thermodynamic stability of 2:1 clay minerals with partially occupied by hydroxy-Al, suggesting deceleration in the intercalation process and a tendency of transforming clay minerals from extensive into partial intercalation.Index terms: HIS, HIV, organic carbon, soil management systems, mineral stability.(

Chemical and mineralogical changes in a Brazilian Rhodic Paleudult under different land use and managements

“…The soil solution was extracted from samples from the 0.0-2.5 cm layer by centrifugation, according to the method described by Inda et al (2010). Immediately after extractions, the pH and electrical conductivity were determined.…”

“…On the other hand, the cattle droppings in GrP resulted in significant increases in most elements such as K, Na, due to the high concentration of these elements in bovine urine; and P, Mg and Ca, due to their concentration in cattle dung (Moreira et al, 2010). Also noteworthy was the significant increase in Fe, Al and Si concentrations in the soil solution under grazed pasture (GrP), which may be associated with processes of mineral dissolution/transformation (Azevedo et al, 1996;Officer et al, 2006;Zanelli et al, 2007;Inda et al, 2010;.…”

“…The stability of mineral lines were selected as proposed by Azevedo et al (1996) and Inda et al (2010) and represent 2:1 clay minerals vermiculite and smectite with partial Al-hydroxy interlayering (P-HIS and P-HIV) together with kaolinite, gibbsite, amorphous silica, and quartz. In the stability diagram, the points representing the land use and management systems with NGr, NTM and NTPL were between the lines of quartz and amorphous silica, indicating that amorphous silica formation is not intense.…”

“…Also under controlled conditions, the formation of organo-mineral complexes demonstrated the effectiveness of some organic binders to promote depolymerization of the interlayers of HIV and HIS clay minerals (Indraratne et al, 2007;Huang et al, 2007). In soil under intensive grazing, the transformation HIV → V was attributed to the pH increase and factors resulting from concentrated urine and manure droppings (Officer et al, 2006).…”

“…On the other hand, no transformation of HIS clay minerals was detected by XRD in an Oxisol limed with 40 Mg ha -1 limestone, after 23 years (Azevedo et al, 1996), and in an Oxisol, 26 years after replacing CT by NT (Inda et al, 2010). However, in both studies, the reduction in Al activity in the soil solution, as well as the thermodynamic stability diagrams indicate that these anthropic actions created favorable chemical conditions in the soil solution for a delay in the intercalation of interlayered hydroxy-Al.…”