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Analytical data on the heavy metal content of humic acid extracted from the surface soil samples of a wooded area in southern Sardinia and correlations between soil and humic acid metal content are reported. A tentative approach to the determination of humic acid-heavy metal complex stability constants, based upon Langmuir's isotherm is proposed.

The knowledge of the interactions between metals and soil components is of great importance to evaluate the availability of the trace elements to plants as well as the potential danger of metals to soil and water beds. The main factors affecting the equilibrium and interaction meccanisms between metals and the most active soil costituents in the absorption processes are discussed in this paper.

Four different doses of olive mill waste were spread on the calcareous soil of a vineyard. No significant alteration of the soil properties was observed even at the highest dose of OMW whereas an active dynamism of organic matter and mineral elements was registered.

This preliminary note considers 19 profiles of Sardinian soils developed on hard limestone, dolomitic limestone and dolomite of different age and territorial condition, reporting on the description of the profiles and their physical, chemical and mineralogical characteristics. The results indicate that the soils examined belong to xeric subgroups of three orders: Entisols, Inceptisols and Alfisols. All the profiles show a clay texture and the clayey constituents are related to the degree of soil evolution.

The adsorption of four s-triazines on the A1-horizon of a brown soil from Sardinia was studied. The adsorption isotherms showed to be essentially linear. Prometryne, hydroxipropazine and prometone were highly absorbed at pH 5, scarcely at pH 2. Propazina behaved differently, showing the highest adsorption at low pH values. Adsorption was affected by the acidity of aqueous systems and tends to increase with a decrease in pH, reaching a maximum in the vicinity of the pK of the respective compounds.

Variations of permanent and pH-dependent charges of soil clays subjected to thermal and chemical treatments were studied. The permanent charge was considerably reduced either on heating samples at 400°C or on acid treatment. A strong hysteresis of the permanent charge occurred in the heated samples treated with NaOH. The decrease in permanent charge after attack with HCl was due to vermiculite decomposition. The different behaviour of the pH-dependent charge was attributed to the structural changes which different treatments can give rise on the interlayer materials.

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 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.

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.

The adsorpition of six s-triazines of the chloro- and methoxy-analogue series on a bentonite from Uri (Sardinia) was studied. The H-bentonite shows a higher adsorption than the Na-bentonite. The order of adsorbabiIity of chloro-s-triazines was trietazine > atrazine > propazine; by me· thoxy-s-triazines it was simetone > atratone > prometone. The amount of simetone adsorbed by the H-bentonite occurred in excess of the CEC. The relationship between adsorption, solubility and lenght of the lateral chain of the s-triazine was confirmed. The adsorption was mainly due to van der Waals forces, H-bonding and ionic exchange.