Balwant Singh

Introduction Significant quantities of sulfidic sediments have been reported to have recently accumulated in inland wetlands of Murray Darling Basin due to a combination of long periods of inundation and the entrance of sulfate-rich water (Fitzpatrick and Shand, 2008). Sulfidic sediments have a capacity to produce copious amount of acidity on exposure to aerobic conditions (Fitzpatrick and Shand, 2008). These processes will cause soil acidification if the buffering capacity of soil is less than the amount of acidity produced. The dissolution of phyllosilicate minerals may occur if soil pH decreased below 4 in acid sulfate soils (ASS). The quantification of the mineral dissolution rates in ASS is imperative to understand the mechanism and parameters controlling the acid neutralization processes and their impact on the soil environment. The aim of this study was to investigate the dissolution behaviour of the clay material from an inland ASS in solutions with the composition similar t...

Liming and mulching are common agricultural management practices. However, there is limited knowledge on the temperature sensitivity of carbon (C) release in acidic soils amended with lime and mulch. We conducted laboratory incubation experiments for 96 days at 20°± 1 and 40 °C ± 1 using an acidic Chromic Luvisol. The experiments consisted of five treatments viz: soil only (S), soil + lime (S + L), soil + mulch (S + M), soil + mulch + lime (S + M + L) and soil + mulch + 2L (S + M + 2L). Mulch was applied at the rate of 0.5% w/w (M) in the form of sugarcane trash and lime was added at two rates, i.e. 0.46 (L) and 0.92 (2L) % w/w using analytical grade calcium carbonate. The proportions of C released from lime (δ13C of –8.67‰), mulch (–13.02‰) and soil (–25.2‰) were quantified using their distinct δ13C values and a simple linear mixing model. During the 96-day incubation period, in the absence of mulch addition between 64% and 100% of the applied lime C was released as CO2 at both inc...

Hypotheses: 1) rhizosphere effects would enhance lime dissolution and subsequent CO 2 effluxes; and 2) liming would increase the mobility of dissolved inorganic C (DIC) and dissolved organic C (DOC) in the presence of growing wheat plants. Methodology: Soil sampling & characterization • Subsurface (10–20 cm) sample of a highly acidic (pH 1:5H2O = 5.2) red Kandosol was collected from a long-term acidification field experiment at the Agricultural Institute in Wagga Wagga, NSW. • The soil contained 1.4 % organic C, 72 % sand, 8% silt and 20 % clay. Plant growth • 2.8 kg soil was packed into each PVC column. The following basal nutrients (mg/column), dissolved in water to maintain 60% WHC, were applied to all soil columns: KH 2 PO 4 (1000), (NH 4) 2 SO 4 (215), ZnSO 4 .7H 2 O (18), MnSO 4 ·H 2 O (6), CuCI 2 .2H 2 O (8), H 3 BO 3 (2) and Na 2 MoO 4 ·2H 2 O (1). Initially, nitrogen was applied in the NH 4 form [(NH 4) 2 SO 4 ], while the later additions were in the NO 3 form [Ca(NO 3) 2 a...

Land-use and management practices on limed acidic and carbonate-bearing soils can fundamentally alter carbon (C) dynamics, creating an important feedback to atmospheric carbon dioxide (CO2) concentrations. Transformation of carbonates in such soils and its implication for C sequestration with climate change are largely unknown and there is much speculation about inorganic C sequestration via bicarbonates. Soil carbonate equilibrium is complicated, and all reactants and reaction products need to be accounted for fully to assess whether specific processes lead to a net removal of atmospheric CO2. Data are scarce on the estimates of CaCO3 stocks and the effect of land-use management practices on these stocks, and there is a lack of understanding on the fate of CO2 released from carbonates. We estimated carbonate stocks from four major soil types in Australia (Calcarosols, Vertosols, Kandosols and Chromosols). In >200-mm rainfall zone, which is important for Australian agriculture, t...

ABSTRACT a b s t r a c t Lime is commonly used to overcome soil acidification in agricultural production systems; however, its impact on inorganic and organic soil carbon dynamics remains largely unknown. In a column experi-ment, we monitored rhizosphere effects on lime dissolution, CO 2 effluxes, and the concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in leachate from an acidic Kandosol. The experiment consisted of four treatments viz: soil only (control), soil þ lime, soil þ wheat, and soil þ lime þ wheat. We measured CO 2 -C effluxes at 7, 43 and 98 days after planting (DAP) and leachate was collected at 56 and 101 DAP. The soil CO 2 -C efflux rate increased significantly with lime addition at 7 and 43 DAP compared to control. At 43 DAP, the largest increase in CO 2 -C effluxes was observed in the lime þ wheat treatment. However, at 98 DAP similar CO 2 -C effluxes were observed from wheat and lime þ wheat treatments, suggesting that most of the lime was dissolved in the lime þ wheat treatment. Both DOC and DIC concentrations in the leachate increased significantly with lime and wheat only treatments (cf. control). In contrast to DOC, there was an increase in the DIC concentration in the soil leachate from lime þ wheat treatment columns at 101 DAP (significant wheat  lime interaction), thus, accentuating the pronounced role of wheat roots. We conclude that plant mediated dissolution of lime increased the concentration of DIC in the soil leachate, while both liming and presence of plants enhanced DOC leaching.

The prevalence of sulfidic sediments in inland wetlands has been recognized in the last few years in many parts of the world including Australia (Lamontagne et al., 2006). Under conditions of very high salinity, the oxidation of iron sulfide minerals in these sediments ...

... Titre du document / Document title. Potassium and magnesium in clay minerals of some Brazilian soils as indicated by a sequential extraction procedure. Auteur(s) / Author(s). MELO VF (1) ; SCHAEFER CEGR (2) ; NOVAIS RF (2) ; SINGLY B. (3) ; FONTES MPF (2) ; ...

Although association between mineral and biochar carbon have been speculated in some studies, still there is no direct evidence for the influence of individual clay minerals on the mineralization of biochar carbon in soils. To address this, we conducted an incubation study using monomineralic soils constituted by separately mixing pure minerals, i.e., smectite, kaolinite, and goethite, with a sandy soil. Switch grass biochar (400 °C) was added to the artificial soils and samples were incubated for 90 days at 20 °C in the laboratory. The CO2-C mineralized from the control, and biochar amended soil was captured in NaOH traps and the proportion of C mineralized from biochar was determined using δ13C isotopic analysis. The clay minerals significantly decreased the cumulative total carbon mineralized during the incubation period, whereas biochar had no effect on this. The least amount of total C was mineralized in the presence of goethite and biochar amended soil, where only 0.6% of the ...

ABSTRACT Mulch Inorganic and organic carbon Q 10 Acidic soil Lime is commonly applied on agricultural lands for ameliorating soil acidity. However, lime dissolution and its concomitant contribution to carbon dioxide (CO 2) fluxes with the addition of organic residues at varying temper-atures in acidic soils are not well known. We conducted laboratory incubation experiments for 96 days (20 +/− 1 °C and 40 +/− 1 °C) to quantify the priming effects of lime (0.46 and 0.92% w/w) and mulch (0.5% w/w) additions on carbon (C) release in a Chromic Luvisol. The C released from lime (δ 13 C of −8.67‰), mulch (−13.02‰) and soil (−25.2‰) was quantified using their distinct δ 13 C values. Total lime derived C in soils without mulch constituted approximately 32% and 17% of the total C fluxes at 20 °C and 40 °C, respectively. During the 96-day incubation period, in the absence of mulch addition between 64% and 100% of the applied lime C was released as CO 2 at both incubation temperatures. Furthermore, lime derived, mulch derived and soil de-rived C increased by 59, 48 and 284% respectively, when the incubation temperature was increased from 20 °C to 40 °C. These results suggest that mineralization of native soil C was more sensitive to temperature than the C released by lime dissolution and mulch mineralization. Temperature sensitivity of soil derived C was lower in treatments with mulch and lime addition compared to soil without C amendments. We obtained a Q 10 value of 2.41 ± 0.06 for the C released by the lime dissolution in the acidic soil. These findings are important for modelling the contribution of different C sources to atmospheric CO 2 concentrations in soils, such as the acidic limed and mulched soils.

Biochar, a form of pyrogenic carbon, can contribute to agricultural and environmental sustainability by increasing soil reactivity. In soils, biochar could change its role over time through alterations in its surface chemistry. However, a mechanistic understanding of the aging process and its role in ionic nutrient adsorption and supply remain unclear. Here, we aged a wood biochar (550 °C) by chemical oxidation with 5-15% H2O2 and investigated the changes in surface chemistry and the adsorption behavior of ammonium and phosphate. Oxidation changed the functionality of biochar with the introduction of carboxylic and phenolic groups, a reduction of oxonium groups and the transformation of pyridine to pyridone. After oxidation, the adsorption of ammonium increased while phosphate adsorption decreased. Ammonium adsorption capacity was nonlinearly related to the biochar's surface charge density (r(2) = 0.94) while electrostatic repulsion and loss of positive charge due to destruction of oxonium and pyridine, possibly caused the reduced phosphate adsorption. However, the oxidized biochar substantially adsorbed both ammonium and phosphate when biochar derived organic matter (BDOM) was included. Our results suggest that aging of biochar could reverse its capacity for the adsorption of cationic and anionic species but the inclusion of BDOM could increase ionic nutrient and contaminant retention.

ABSTRACT The structural and physical effects of partially substituting Cd for Fe in goethite have been investigated. The solubility of Cd2+ in goethite is ~10 mol.%, i.e. Fe0.905Cd0.095OOH. The structures of the substituted goethites have been refined, using the Rietveld method, from synchrotron X-ray powder diffraction data. There is a progressive increase in the size of the unit-cell parameters and unit-cell volume, upon the incorporation of much larger Cd2+ ion (0.95 Å) compared with Fe3+ (0.645 Å) in the goethite structure, together with a reduction in crystallinity. Transmission electron microscopy measurements confirm the crystallite size decreases as the Cd2+ content increases in goethite structure.

ABSTRACT Significant amounts of sulfuric acid (H2SO4) rich saline water can be produced by the oxidation of sulfide minerals contained in inland acid sulfate soils (IASS). In the absence of carbonate minerals, the dissolution of phyllosilicate minerals is one of very few processes that can provide long-term acid neutralisation. It is therefore important to understand the acid dissolution behaviour of naturally occurring clay minerals from IASS under saline-acidic solutions. The objective of this study was to investigate the dissolution of a natural clay-rich sample under saline-acidic conditions (pH 1–4; ionic strengths = 0.01 and 0.25 M; 25°C) and over a range of temperatures (25°C – 45°C; pH 1 and pH 4). The clay-rich sample referred to as Bottle Bend clay (BB clay) used was from an IASS (Bottle Bend lagoon) in south-western New South Wales (Australia) and contained smectite (40%), illite (27%), kaolinite (26%) and quartz (6%). Acid dissolution of the BB clay was initially rapid, as indicated by the fast release of cations (Si, Al, K, Fe, Mg). Relatively higher Al (pH 4) and K (pH 2-4) release was obtained from BB clay dissolution in higher ionic strength solutions compared to the lower ionic strength solutions. The steady state dissolution rate (as determined from Si, Al and Fe release rates; RSi, RAl, RFe) increased with decreasing solution pH and increasing temperature. For example, the highest log RSi value was obtained at pH 1 and 45°C (-9.07 mol g-1 s-1), while the lowest log RSi value was obtained at pH 4 and 25°C (-11.20 mol g-1 s-1). A comparison of these results with pure mineral dissolution rates from the literature suggests that the BB clay dissolved at a much faster rate compared to the pure mineral samples. Apparent activation energies calculated for the clay sample varied over the range 76.6 kJ mol–1 (pH 1) to 37.7 kJ mol–1 (pH 4) which compare very well with the activation energy values for acidic dissolution of monomineralic samples e.g. montmorillonite from previous studies. The acid neutralisation capacity (ANC) of the clay sample was calculated from the release of all structural cations except Si (i.e. Al, Fe, K, Mg). According to these calculations an ANC of 1.11 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 (I=0.25 M, 25°C) compared to an ANC of 0.21 kg H2SO4/tonne clay/day at pH 4 (I=0.25 M, 25°C). The highest ANC of 6.91 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 and at 45°C (I=0.25 M), which is more than three times higher than the ANC provided under the similar solution conditions at 25°C. In wetlands with little solid phase buffering available apart from clay minerals, it is imperative to consider the potential ANC provided by the dissolution of abundantly occurring phyllosilicate minerals in devising rehabilitation schemes.