A Comparison of Mineral Weathering Trends Between Two Management Systems on a Catena of Loess‐Derived Soils

Abstract

This study was an attempt to predict potential long‐term mineralogical transformation trends in soils under continuous no‐tillage management using the in situ soil solution composition as a sensitive index of changes occurring in the soil system. Mineralogical and soil solution compositions of surface and subsurface horizons of a catena of loess‐derived soils (Memphis, Grenada, Calloway) under continuous (16 yr) no‐till (NT) and conventional‐till (CT) management suggested a shift in weathering patterns as a result of the differential tillage management. This shift was evident primarily as a buffer effect of the NT management on drainage characteristics. Interstitial soil solutions of surface NT horizons were generally two to three times higher in Si and K than respective surface CT horizons. The elevated soluble Si and K concentrations maintained in the NT horizons correlated well with increases in organic matter content. The Si‐enrichment of the NT‐solutions combined with the reduced Al3+ activities, due to increased complexation, appeared to favor a hydroxyinterlayered vermiculite/vermiculite metastable state over the hydroxyinterlayered vermiculite/kaolinite of the CT system. This slowdown of the weathering process under continuous NT management should have important implications on K equilibria of these soils.

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

“…This possible combined effect of pH (liming) and organic matter will need to be assessed in future studies in long-term experiments to deepen the understanding of possible management minerals with extensive intercalation (HIS-E or HIV-E) into those with partial intercalation (HIS-P or HIV-P). According to Karathanasis et al (1989), this does not necessarily lead to a reversal of the weathering sequence in this soil, but shows that the soil system has been altered in such a way that the precursor or intermediate minerals (2:1 clay minerals with partial intercalation with Al hydroxyl) may be becoming stable in the new pedo-environment.…”

“…The organic matter accumulation in the top soil layer under NT contributed to a three-fold increase in the content of dissolved organic carbon (DOC) over the CT soil. DOC can be associated with the significant Al increase (not found in the sorption complex) and Si in the solution of NT soils (Karathanasis & Wells, 1989). According to Azevedo et al (1996), the effect of NT on the soil solution can also be shown in the increase of S in solution, mainly derived from the mineralization of organic matter.…”

“…These alterations in the mineralogy of iron oxides were attributed to changes in the pedo-environmental conditions resulting from the implementation of NT, which normally leads to an increase in organic matter content (Ciotta et al, 2002;Costa et al, 2004;Dieckow et al, 2009), an increase in moisture and the residence time of water, in addition to a decrease in soil temperature (Salton & Mielniczuk, 1995;Costa et al, 2003). Due to the close relationship of these effects with soil and climate variables, such pedoenvironmental changes destabilize the system and a new dynamic equilibrium is established that can also gradually affect the stability of 2:1 clay minerals with interlayered Al hydroxyl (Karathanasis & Wells, 1989;Azevedo et al, 1996;Officer et al, 2006), frequently found in the clay fraction of soils in the subtropical regions of Brazil (Pötter & Kämpf, 1981;Curi et al, 1984;Ker & Resende, 1990;Kämpf et al, 1995;Almeida et al, 2000).…”

“…HIV and HIS clay minerals are considered stable in moderately acidic pedo-environments with low organic matter content (Kämpf & Curi, 2003). However, changes in the formation conditions, resulting from the implantation of soil conservation management systems, can destabilize/transform these minerals by the partial removal of Al hydroxyl polymers from the interlayers (Karathanasis & Wells, 1989;Kämpf & Curi, 2003).…”

Iron oxides and quality of organic matter in sugarcane harvesting systems

“…In contrast, the degree of humification differed markedly (Mendonza et al, 2000;Guimarães et al, 2013) and was higher in the mechanically harvested area. The increased humification of this area, together with the increased MCD values of goethite in it, suggests a tendency toward a new dynamic equilibrium via gradual mineralogical changes in the soil system (Karathanasis & Wells, 1989). Inda Jr. & Kämpf (2005) examined the selective dissolution of Fe oxides and concluded that goethite heterogeneity was possibly a result of pedoenvironmental changes during the pedogenetic process; such changes altered the factors governing Al 3+ activity in the soil solution (e.g.…”