Transfer of metal ions in the soil-root interface: influence of copper(II) on the stability of the fibrils

A network of Ca-polygalacturonate arranged in fibrils similar to those of plant roots (Gessa C. and Deiana S., (1990); C.Gessa and Deiana S., (1990)) constitutes a very useful model far the study of the ionic transfer both in the soil-root interface and in the apoplast. Due to the fact that important properties of the network, such as the hydration degree and the absorption phenomena, vary dramatically with the reticulating ion (Gessa C. and Deiana S., (1989)), this note reports on the influence of the metal ions on the fibrillar structure of the network and gives further information about the transfer of the metal ions to the roots

Contributo dell'argilla e della sostanza organica alla capacità di scambio cationico delle terre brune della Sardegna Nord-Orientale

The contributions of clay and organic matter relative to 24 samples collected from non calcic brown soils of N-W Sardinia - were measured using statistical analyses. Within the limits of the standard errors the regression coefficients of day and organic matter increase linearly with pH. The average contribution to CEC of day decreased from 64% at pH 3 to 300% at pH 8. The clay CEC was 30, 34, 39 meq per 100 g. al pH 3,5 and 8, respectively, while that of the organic matter was 62, 131, 231 meq per 100 g. The high increase of CEC between pH 5 and 8 was interpreted in view of eventual liming of cultivable soils

Effetto dei detersivi commerciali sullo sviluppo di alcune specie vegetali di interesse agrario

Experiments have been realized on some agricultural vegetable species to study their growth behaviour in the presence of detersive, using to the purpose faur commercial detersives. The greatest phototoxic effects are felt by Lolium. Medicago and Tripholium. The detersive containing the no-ionic tensio-active shows the most depressing action

Effects of Al substitution on goethite formation

Goethites containing up to 32.7 mole % Al were synthesized and characterized through diffractometry, spectrometry, DSC and chemical techniques. Results indicate that crystal growth was favoured or hindered depending on the percentage of aluminum incorporated into the structure. Goethites to which 5-10 mole % Al were initially added crystallized best, as shown by the highest crystallite dimensions calculated from X-ray and Mössbauer analyses, and by the lowest surface areas values. Over such substitution degree goethite crystallization was hindered and for sample synthesized in presence of 40 mole % Al the separation of a discrete amount of gibbsite and bayerite occurred. Both crystallinity and Al-substitution degree influenced the goethite dehydroxylation endothermic peak temperature playing a competitive action in the peak shift. In fact, the increase in the thermal stability induced by the presence of Al3+ ions into the structure was counteracted by the decrease due to the particle size reduction. The stabilizing effect of aluminum was confirmed by the oxalate treatment which removed from the Al-free sample a Fe amount higher than that from the sample containing about 20 mole % Al, although both had similar crystallinity

Transfer of metal ions at the soil-root interface: role of VO²⁺ on Fe³⁺ mobilization from a Fe(III)-network

This note reports the role of VO(IV) on Fe(III) mobilization from a Fe(III)-polygalacturonate network. The effect of the reaction on the physical properties of the system is also considered

Role of the polygalacturonate network on the iron (III) reduction by caffeic acid

This communication reports the role of polygalacturonate network on the Fe(III) reduction by caffeic acid. The effect of phosphate ions on the redox reaction is also considered

Le Terre brune della Gallura

The brown soils of Gallura have been developed chiefly on granites whose formation dates back to Ercinic Orogenesis. These soils are characterized by little deep profiles, generally lower than 50 cm, well drained mainly because of small day contcnts (7.83 - 15.35%). The day distribution along the profile is rather uniform. The permanent charge of the inorganic colloidal fraction oscillates between 20 and 40 meq/100g, while the pH dependent charge is frequently higher than the permanent charge. The exchange complex of soil is chiefly calcium saturated. The base saturation percentage is rather low, varying between 0.30 and 0.58, but remains pratically constant along the profile; the small differences between the two horizons could be explained on the basis of the soils' sampling time rather than the basic cations leaching. Leached brown soils are also present in Gallura, but they very scarce. The organic matter of the soils rarely overcomes 7%, in the superficial horizons and decreases to values usually below the 3%. In the more typical brown soils the C/N ratio is below 14. The optical properties, the potentiometric and conductometric curves reveal a dose resemblance between the humic acids of these soils and those of Campeda andosoils

The Fate of Herbicides in Soil

The prediction of the movement and fate of herbicides in soils represents an important startegy in limiting their environmental impact. The chemico-physical properties of herbicides affect thier behaviour in soil and regulate their interaction mechanisms with organic and inorganic soil phases. Among these, dissolved organic matter plays an important role bacause it influences the mobility of herbicides by complex interactions that can facilitate or reduce the movement of chemicals along the soil profile. The knowledge of soil phase characteristics and the mechanisms involved in herbicide transformation can help to understand the fate of herbicides in soil

Role of the caffeic acid oxidation products on the iron mobilization at the soil-root interface

Previous results show that the reduction of Fe(III) by caffeiic acid (CAF) is strongly influenced by the pH of the reaction medium (DEIANA et al., 1995). In particular, it has been found that al pH > 3.8 the reducing activity of CAF towards the Fe(III) ions in solution is low, but it increases when Fe(III) is complexed as Fe(III)-polygalacturonate. The mobilization of the Fe(II) ions, which form upon the Fe(III) reduction, has been shown to depend mainly on the nature of the Fe(III)-polygalacturonate complexes (DEIANA et al., 1994a). In particular, it bas been observed a high redox activity of CAF towards Fe(III) when the metal ion is coordinated by the carboxilic groups of the macromolecule. The Fe(III) reduction has been found to decrease when an oxydrilic group was inserted in the Fe(III) coordination sphere. The Fe(II) produced partly diffuses into the external solution and partly is still strongly held by the polysaccharidic matrix. The oxidation of CAF by Fe(III) gives rise to the formation of products (OP) with different polymerization degree, some of which are similar to those found in natural systems (DEIANA et al., 1994b). In order to determine the role of these products in the Fe(III) reduction as well as in the mobilization of the Fe(II) produced it was set up an electrochemical method to synthetize these products (DEIANA et al., 1994b). Here are reported some results about the interaction which establish between the CAF oxidation products and iron in both oxidized and reduced form

Stereochimica di alcuni acquo-complessi assorbiti su bentonite

The stereochemistry of some hydrated ions on the interlamellar surfaces of bentonite has been investigated by spectroscopic methods. The coordination of adsorbed ions estimated on the basis of d001 values has been confirmed by diffuse reflectance and ESR spectra. When the d001 value is ~ 12.4 Å a monolayer of water occupies the « interlayer »; the ion is coordinated to four water molecules in the xy plane and to two silicate oxygens along the z axis. When the d001 value is 14-3 Å two layers of water occupy the «interlayer »; the ion is octahedrally coordinated to six water molecules and the symmetry axis of the acqueous-complex is inc1ined with respect to the sili· cate layers at an angle of 45º When the d001 value is ~15.0 Å, three layers of water are present in the interlayer; the ion is octahedrally coordinated to six water molecules but the symmetry axis is perpendicular to the silicate layers