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Prolonged leaching of mineral forest soils with dilute HCl solutions: the solubility of Al and soil organic matter 总被引：5，自引：0，他引：5
Long-term acidification has been shown to result in a considerable decrease in the amount of organically bound soil Al and in a gradual decrease in the solubility of Al. We examined the solubility of soil organic matter (SOM) and Al in four acid mineral soils (one Arenosol Ah, two Podzol Bh, and one Podzol Bs) as they were leached sequentially using a solution containing 0.001 m HCl and 0.01 m KCl. The acid leaching resulted in relative decreases in Al that were 2–6 times greater than for organic C. The organic C and Al dissolved by the acid leaching originated mainly in the pyrophosphate-extractable fraction of the elements. Protonation seems to be a major mechanism in stabilizing the residual SOM, as indicated by small changes in effective cation exchange capacity with the degree of acid leaching. In the samples of Podzol Bh and Arenosol Ah soils the solubility of Al (defined as log10 {Al3+ } + 1.5pH) in equilibrium suspensions (0.01 m KCl) was closely related to the ratio of pyrophosphate-extractable Al to pyrophosphate-extractable organic C. The Podzol Bs sample probably contained a small amount of a surface-reactive Al(OH)3 phase, which rapidly became depleted by the acid leaching. 相似文献
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Isolates representing 11 anastomosis groups (AGs) of Rhizoctonia solani from various geographic locations and host plants were tested for virulence on soybean leaves at 15, 20, 25, 30, and 35°C, and on soybean seedlings at 20, 25, and 30°C. Numbers of infection cushions formed on soybean leaves were determined using light microscopy. Isolates of AG-1 IA, AG-1 IB and AG-5 were more virulent on soybean leaves at 20, 25, and 30°C than isolates of AG-1 IC and AG-4. Maximum numbers of infection cushions were formed on soybean leaves by AG-1 (IA, IB, and IC), AG-4, and AG-5 at 25 and 30°C. The other AGs tested did not form infection cushions on soybean leaves although some caused minimal disease severity. Isolates of AG-1 IA formed significantly more infection cushions and caused greater disease severity than AG-1 IB and other isolates at 35°C. Maximum seedling infection, based on per cent area of hypocotyl region covered by lesions occurred at 25 C for AG-1 (IA, IB, and IC) and AG-4. Isolates of AG-5 caused greater seedling infection at 20°C than at 25 and 30°C. The other AGs tested caused only minimal damage to the seedlings. Isolates of AG-4 and AG-5 are not known to cause Rhizoctonia foliar blights of soybean in Louisiana, but their potential to be destructive foliar pathogens is confirmed. 相似文献
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Infection cushions were formed by isolates of Rhizoctonia solani , anastomosis group 1 IA (AG-1 IA, aerial blight) and AG-1 IB (web blight) on leaves of all 10 soybean cultivars tested. Isolates of AG-1 IA and IB did not form infection cushions on soybean leaf surface replicas of either resistant or susceptible cultivars. More infection cushions were formed by isolates of AG-1 IA and IB on collodion membranes placed over leaves of susceptible cultivars compared with resistant cultivars. Isolates of AG-1 IC. AG-4 and AG-5, also formed infection cushions on soybean leaves. However, the isolates of other anastomosis groups did not form infection cushions on soybean leaves. Differential induction of infection cushion formation by the leaves of various plant species was observed, AG-1 IA formed infection cushions on more graminaceous hosts than AG-1 IB, Our results suggest that a chemical stimulus is needed for infection cushion formation. Glucose and 3- O -methylglucose repressed disease severity caused by AG-1 IA and IB isolates to the same extent. Disease severity and the number of infection cushions formed on leaves of ten soybean cultivars were correlated. Fewer infection cushions were formed on resistant cultivars than on susceptible cultivars. 相似文献
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The molecular weight distribution of humic substances in soil solutions from a dystric cambisol and an orthic podzol were determined by high-performance gel filtration chromatography (Toyo Soda TSKgel G2000 SWXL column). The retention volumes of humic substances were compared to those of narrow molecular weight distributed poly-styrenesulphonates with known molecular weight. A change in mobile phase pH or ionic strength usually resulted in an almost identical change in retention volume for the polystyrenesulphonates and the bulk of humic substances. The possibility of using the former to calibrate the column is discussed. The molecular weight at peak maximum was 1120–1190 and 1800 for the cambisol and podzol samples, respectively, using polystyrenesulphonates as molecular weight standards. No pretreatment of samples was used, but ion exchange is recommended for samples with high Al concentrations. 相似文献
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wham , an equilibrium chemical model for soils, waters and sediments, centred on a discrete-site/ electrostatic model of humic substances (HS), has been used to analysae batch titration data for organic and mineral horizons of acid soils. In most cases, tolerable fits were obtained by optimizing the soil contents of HS and aluminium, while keeping the model parameters (site densities, equilibrium constants, electrostatic terms) fixed. The optimized contents agreed reasonably with those estimated by chemical extraction. For some mineral soil samples, low in HS and high in aluminium, fitting of the titration data was improved by assuming the formation and dissolution of A1(OH)3 and adjusting its solubility product. Solid-solution distributions of base cations (Na+, Mg2+, K+, Ca2+, NH+4) could be explained by non-specific counterion accumulation, with a small degree of selectivity. The WHAM sub-model for fulvic acid sorption accounted approximately for observed aqueous-phase concentrations of organic carbon and organically-complexed aluminium. 相似文献
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Aluminium solubility related to secondary solid phases in upper B horizons with spodic characteristics 总被引：2，自引：0，他引：2
We examined the aluminium solubility in the upper B horizon of podzols and its relation to the solid phase of the soil in 60 samples covering a pH range from 3.8 to 5.1. Solid phases were characterized by extractions with acid oxalate and pyrophosphate (pH 10). The solubility of Al was studied in a batch experiment in which samples were equilibrated with 1 m m NaCl at 8°C for 5 days. We also monitored the dissolution kinetics of Al and Si, in some samples. The oxalate and pyrophosphate extractions suggested that secondary Al was mainly organically bound in most soils, and imogolite-type materials seemed to constitute much of inorganic secondary Al. No single gibbsite or imogolite equilibrium could explain Al3+ activities. In all samples Al solubility, defined as log{Al3+ } + 1.65pH, was closely related to the molar ratio of aluminium to carbon in the pyrophosphate extracts (Alp /Cp ). Solubility increased with the Alp /Cp ratio until the latter reached ≈ 0.1. This indicated that solubility was controlled by organic complexation, at least when Alp /Cp was small. Silica dissolved slowly in most soils used in the kinetic experiments. We conclude that imogolite-type materials in the upper B horizon dissolved slowly because of coating with humic substances or ageing or both. 相似文献
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