Changes In Exchangeable Cations Research Articles

Changes in exchangeable cations and micronutrients in soils and grains of long-term, low input cropping systems of subtropical Australia

Demand for agricultural products is increasing, but there remains considerable uncertainty regarding many of the impacts of long-term cropping systems on soil properties. Using six soils from low input cropping systems of subtropical Australia, the effects of long-term cultivation (≤70y) on three macronutrient cations (Ca, Mg, and K) and three micronutrient cations (Cu, Zn, and Mn) was examined. For Ca, Mg, and K, exchangeable concentrations generally remained constant and were not influenced by the period of cultivation. As a result, concentrations of these nutrients in grain tissues of wheat (Triticum aestivum) also remained constant over time. However, concentrations of DTPA-extractable Cu, Zn, and Mn often (but not always) decreased significantly over time, with Cu decreasing 21%, Zn by 34%, and Mn by 46% (when averaged across soils where significant differences were found). In some soils, these decreases in DTPA-extractable micronutrients also resulted in concomitant decreases in grain tissue concentrations. These decreases in DTPA-extractable Cu, Zn, and Mn concentrations do not result only from the export of nutrients in grain tissues, but also, from an increase in soil pH caused by a cultivation-induced mixing of alkaline subsoil into the surface soil. The data presented here demonstrate the potential impact of long-term cropping on nutrient availability, and in particular, the need to consider changes in nutrient availability and its potential impact on plant and human nutrition.

Effects of incubation times and moisture regimes on pH values and exchangeable cations in acid sulfate soils as influenced by application rates of basic slag

Severe acidifications in acid sulfate soils (ASSs) have occurred worldwide due to sulfuric acidity, which requires sustainable measures for their reclamation. Accordingly, an incubation study was conducted with the topsoil of two different ASSs (Cheringa and Badarkhali) to evaluate the effects of basic slag (BS; size <1 mm, pH 9.6, Ca 20.8%, Mg 9.8%, etc.), on reduction of acidity and changes in exchangeable cations. It is noted that BS is a byproduct of steel industry in Bangladesh and can be collected almost free of charge. These soils received BS at the rate of 0 (T0), 11 (T1), 22 (T2) and 33 (T3) t ha−1 under various moisture regimes (saturated condition M1,, i.e., 100% moisture content, wetting–drying cycles of 100 and 50% moisture M2, and moisture at field condition M3, i.e., 50%). The impacts of these treatments on some selected parameters in these soils were studied within 180 days of incubation. The application of BS was found to increase the pH of soils from 3.6 to 5.1 for Cheringa, 3.9 to 5.2 for Badarkhali soils at the end of incubation. These increments were more striking with the highest doses of BS under saturated moisture conditions in both of the soils. The ECe of the soils was not much influenced by the application of BS regardless of time. The treatments exerted significant (P ≤ 0.05) effects on exchangeable cations in different periods of incubation. The striking changes were recorded for the rate of increments of Ca2+ and Mg2+, which were about 2–3 times higher for Ca and more than 2 times higher for Mg2+ compared with the control after 180 days of incubation. These results suggest that the application of BS not only increased the Ca2+ to the higher amount than that of the increment of Mg2+ in the soils, but also improved one of the important criteria of Ca2+ and Mg2+ ratio in the soils.

Effect in glyphosate adsorption on clays and soils heated and characterization by FT–IR spectroscopy

The main achievement of this paper is the determination of mineral structural changes in soils from three different sites of Paraná State, Brazil caused by heating and their effect on glyphosate (GPS) adsorption. This work has also shown that pH and point of zero charge (pH pzc) of soils and clays change after heating because of cations (Na +, K +) exchanges or due to changes in mineral structure. The concentration of exchangeable Al 3+ increased after heating Londrina soil and kaolinite samples at 650 °C, and decreased for all other samples. Cation exchange capacity (CEC) decreased for all soil samples and clays, bentonite and montmorillonite, and increased for kaolinite. These changes have been related to changes in exchangeable cations and OM. The major FT–IR spectra changes occur when the samples are heated at 650 °C because of the dehydroxylation of kaolinite and bentonite. The interaction between GPS and Londrina and Tibagi soil and kaolinite samples occurs through the GPS phosphate group and metals present in the samples. An interaction between the GPS phosphate group and metals in Floraí soil samples was not observed. It was not observed in the interaction of any samples with GPS after heating to either 280 or 650 °C. Changes in soil structure due to heating probably play an important role in GPS adsorption. The nonadsorption of GPS on soil after burning could be a problem, as the unadsorbed GPS could either leach to ground water or decrease the productivity of some crops.

Senna siamea trees recycle Ca from a Ca-rich subsoil and increase the topsoil pH in agroforestry systems in the West African derived savanna zone

The functioning of trees as a safety-net for capturing nutrients leached beyond the reach of crop roots was evaluated by investigating changes in exchangeable cations (Ca, Mg, and K) and pH in a wide range of medium to long term alley cropping trials in the derived savanna of West Africa, compared to no-tree control plots. Topsoil Ca content, effective cation exchange capacity, and pH were substantially higher under Sennasiamea than under Leucaena leucocephala, Gliricidia sepium, or the no-tree control plots in sites with a Bt horizon rich in exchangeable Ca. This was shown to be largely related to the recovery of Ca from the subsoil under Senna trees. The increase of the Ca content of the topsoil under Senna relative to the no-tree control treatment was related to the total amount of dry matter applied since trial establishment. The lack of increase in Ca accumulation under the other species was related to potential recovery of Ca from the topsoil itself and/or substantial Ca leaching. The accumulation of Ca in the topsoil under Senna had a marked effect on the topsoil pH, the latter increasing significantly compared with the Leucaena, Gliridia, and no-tree control treatments. In conclusion, the current work shows that the functioning of the often hypothesized ‘safety-net’ of trees in a cropping system depends on (i) the tree species and on (ii) the presence of a subsoil of suitable quality, i.e., clay enriched and with high Ca saturation.

Spatial and Temporal Variation in Calcium and Aluminum in Northern Hardwood Forest Floors

Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base cation displacement from the forest floor is not clear, and has been hypothesized to involve mobilization of aluminum from the mineral soil. We attempted to test the hypothesis that losses of calcium from the forest floor were balanced by increases in Al in NewHampshire northern hardwoods. We measured exchangeable (six stands) and acid extractable (13 stands) Ca and Al in horizons of the forest floor over an interval of 15 years. Our sampling scheme was quite intensive, involving 50 or 60 blocks per stand, composited in groups of 10 for chemical analysis. Even at this level of effort, few stands exhibited changes large enough to be significant. Because of high spatial variability, differences would have had to be greater than about 50% to be statistically detectable. Differences in Ca and Al concentrations between Oi, Oe, Oa, and A horizons, however, were readily detected. Acid-extractable Al increased with depth, while Ca concentrations decreased; Ca-to-Al ratios decreased from 8.3 (charge basis) in the Oi to 0.2 in the A horizon. Therefore, a small change in sampling depth, or the inclusion of more or less A horizon material in the forest floor, could cause large differences in measured Ca and Al concentrations. To detect small changes in exchangeable cations over time would require sampling very intensively with careful control for comparability of horizons.

Comparing modelled and observed effects of ash additions on chemistry of a highly acid soil

The chemical composition of soil solutions (field percolates collected in situ and laboratory saturation extracts) and the amount of salt-extractable cations were measured at several microsites (unburnt, moderately burnt, and intensely burnt ashbeds) after a fuel reduction burning in a subalpine Eucalyptus pauciflora forest. Soil samples were collected 1, 58, 375, 745, and 1095 days after the fire, and soil percolates were obtained on 17 occasions during the initial year. A model of coupled equilibria, which includes insoluble salts, multiple cation exchange, and inorganic complexation, was used to describe soil chemical changes after fire and ash addition. The model was able to describe temporal changes in cation concentrations of held percolates and soil exchangeable cations. Measurements of extractable cations using unbuffered salt solution on samples taken immediately after fire suggest immediate changes in exchangeable cations which were related to solubilisation of cations from ash, and not to changes in exchangeable cations in soils. Modelling suggests that under natural conditions the differences in solubility of cations in ash result in slow changes in exchangeable cations extending over a period of 6 years or more. The time required to reacidify the surface layer of ashbed soil was estimated to be 45 years when annual acid input was 0.5 kmol H+/ha.

Changes in soil pH and exchangeable base cations during moist soil storage

Maintaining samples of four moorland soils of low base status from a podzol profile in a field-moist state prior to analysis is shown to result in significant changes in exchangeable cation concentrations, cation exchange capacity and pH within one month, and often larger changes on more prolonged storage. The magnitude of change depends upon the soil horizon and the determination concerned. Changes may be explained in terms of disruption of natural element biogeochemical cycling. The results suggest that in regional surveys, sample preparation and analysis must be completed within a few days of collection.

Retention of added K, Ca and P byPseudoscleropodium purumgrowing under an oak canopy

AbstractRetention of K, Ca and Pby Pseudoscleropodium purum growing under oak in Windsor Forest was examined following treatment, over 9 days, with 10 mol m−3 CaCl2 or KH2PO4 Concentrations of the added elements and Mg were determined in the intercellular, exchangeable (cell wall) and intracellular fractions of the green tissues before nutrient addition and at intervals (0–205 days) afterwards.Increases of cations in the intercellular fraction of treated shoots were transient. Addition of K and Ca markedly increased levels of these cations in the exchangeable fraction and significantly reduced the concentration of exchangeable Mg. The changes in exchangeable cations were progressively reversed under field conditions indicating that their levels are in dynamic equilibrium with element concentrations in precipitation and/or throughfall rather than the result of a continuousaccumulation process.Net uptake of K and Ca into the protoplasts of treated P. purum was slight but substantial net gain (+178%) of P oc...

Changes in exchangeable cations and exchange capacity of soil consequent on oxidation of its organic matter

1. Loss of ignition at 450°C. and the organic carbon content of some shale soils are positively correlated (r = +0·99).2. Base exchange capacities and exchangeable cations were determined on soils, treated and untreated with hydrogen peroxide solution.3. Oxidizing the organic matter lessened the exchange capacities of all samples; the exchange capacity of the organic matter varied from 67·5 to 97·0 m-equiv./1OO g. dry material.