This paper presents the influence of selected methodological aspects on the results of particle‐size distribution (PSD) as measured by the laser diffraction method (LDM). The investigations were carried out using the Mastersizer 2000 with Hydro MU attachment (Malvern Ltd., UK). It was found that for the investigated soils: (1) optimal speed of pump and stirrer was 2500 rpm, (2) optimal measurement time was ≈ 1 min, (3) there are two, practically equivalent methods for soil‐sample dispersion: chemical (with the use of a solution of sodium hexametaphosphate) or physical (by means of ultrasound application for 4 min at a maximum power of 35W), (4) one must not use the chemical and physical dispersing methods simultaneously, because this can lead to aggregation (not dispersion) of soil particles, (5) the Fraunhofer theory (physical models) can be used to convert scattered‐light data to PSD. In the case of the Mie theory, the best results were obtained for a refractive index (RI) in the range of 1.5–1.6 and an absorption index (AI) of 1.0. It was also found that most of the discussed parameters depend on design of the measuring device and on the type and volume of the investigated suspensions. It is necessary, therefore, to explain how the data was obtained every time and to specify the details in the methodological part of the paper.

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A b s t r a c t. The comparison of particle size distributions measured by sedimentation methods and laser diffraction shows the underestimation of the fine (clay) fraction. This is attributed mainly to the shape of clay particles being different than spherical. The objective of this study was to demonstrate differences in the results of particle size distributions of soils determined with the method of laser diffraction using two different dispersion units of the Malvern Mastersizer 2000.K e y w o r d s: particle size distributions, sedimentation, laser diffraction, Mastersizer 2000 INTRODUCTIONParticle size distribution (PSD) of soils is one of the fundamental parameters permamently used in soil science (Brzeziñska et al., 2011; Joó et al., 2010; Nosalewicz and Nosalewicz, 2011; S³awiñski et al., 2011; Tóth et al., 2009). More and more often the determinations of that parameter is made with the use of the method of laser diffraction (Blott and Pye, 2006; Pye and Blott, 2004; Sperazza et al., 2004). The method consists in measuring the intensity of laser light scattered on the particles measured. The intensity of scattered light depends on the size of the particles in the measurement system. The smaller the particle, the greater the angle at which the light is scattered/refracted.The method of laser diffraction has been compared many times with the earlier methods of PSD determinationthe sedimentation methods (Arriaga et al., 2006; Beuselinck et al., 1998; Ry¿ak and Bieganowski, 2010; Tauber et al., 2008). In certain of such reports one can encounter information about underestimation of the fine (clay) fraction content in measurements performed with the method of laser diffraction as compared to the sedimentation methods (Beuselinck et al., 1998; Eshel et al., 2004; Konert and Vanderberghe, 1997). The underestimation of the clay fraction content is attributed mainly to the shape of clay particles being different than spherical (Konert and Vendenberghe, 1997). Those authors pointed out that the divergent results might be also related to problems with the selection of optical parameters for the clay fraction (Eshel et al., 2004) or with the limited measurement range, especially of the older types of apparatus (Beuselinck et al., 1998).Apart from the above potential causes of the underestimated clay content in soils studied careful analysis of the literature on the determination of PSD with the method of laser diffraction leads also to further conclusions. One of the more important reasons for the lack of comparability of results lies in the use of laser diffractometers of various manufacturers or various models (generations) of equipment of this type from a single manufacturer. Another problem is the frequent lack of information -in research publications -on the type/model of apparatus used and/or on its equipment.The objective of this study was to demonstrate differences in the results of PSD of soils determined with the method of laser diffraction using two different dispersion units of the Malvern Masters...

AB ST R ACT : A new practical and precise method for determining soil aggregate stability is described. Four air-dry aggregate fractions (<0.25, 0.25À0.5, 0.5À1.0 and 1.0À2.0 mm) were added to thoroughly stirred water in a Mastersizer 2000 laser diffractometer. The suspension obtained was passed directly through the measuring system. The dynamics of median (equivalent diameter d 50 ) particle-size distribution decrease (interpolated with a logarithmic function) was assumed to be the measure of soil aggregate stability. In order to show the applicability of the new method, the results obtained (for selected and diverse soils) were compared with those from the wet sieving standard method. The main conclusion is that the proposed method is convenient and can be successfully used for the estimation of soil aggregate stability. Moreover, it has wider application because standard sieving methods are restricted to aggregates >0.25 mm whereas, with the use of the laser diffraction method, smaller aggregates can be measured. The energy delivered to the aggregates in the process of aggregate disintegration is more reproducible in the method described here. The method also provides an opportunity to verify that the soil aggregates are completely destroyed (lack of the changes of the median value shows the end of soil aggregate disintegration).

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The database of Polish arable mineral soils is presented. The database includes a lot of information about the basic properties of soils and their dynamic characteristics. It was elaborated for about 1 000 representative profiles of soils in Poland The database concerns: particle size distribution, organic carbon content, acidity-pH, specific surface area, hydrophobicity - solidliquid contact angle, static and dynamic hydrophysical properties, oxidation-reduction properties and selected biological (microbiological) properties of soils. Knowledge about soil characteristics is indispensable for description, interpretation and prediction of the course of physical, chemical and biological processes, and modelling these processes requires representative data. The utility of simulation and prediction models describing phenomena which take place in the soil-plant-atmosphere system greatly depends on the precision of data concerning characteristics of soil. On the basis of this database, maps of chosen soil properties are constructed. The aim of maps is to provide specialists in agriculture, ecology, and environment protection with an opportunity to gain knowledge of soil properties and their spatial and seasonal variability.

Background and aims The acidic exopolysaccharide (EPS) produced by Rhizobium leguminosarum bv. trifolii is required for the establishment of effective symbiosis with compatible host plants (Trifolium spp.). In the rhizobium-legume interaction, early stages of root infection and nodule development have been well studied from a genetic standpoint. However, factors important for colonization of several surfaces by rhizobia, including soil particles and roots, have not yet been thoroughly investigated. The aim of this study was establishing of environmental factors affecting production of EPS by R. leguminosarum bv. trifolii strain 24.2 and the role of this polysaccharide in bacterial surface properties and attachment ability. Methods Besides the wild-type strain, its derivatives differing in the level of EPS produced were used to these analyses. The ability of attachment to abiotic and biotic surfaces of these strains were established using CFU counting experiments. Three-dimensional structure and other parameters of biofilms formed were characterized in confocal laser scanning microscopy. Electrokinetic (zeta) potential of rhizobial cells were determined using Laser Doppler Velocimetry. Results It was evidenced that the ability of R. leguminosarum bv. trifolii to produce EPS significantly affected bacterial attachment and biofilm formation on both abiotic and biotic surfaces. In addition, the presence of this polysaccharide influenced the zeta potential of rhizobial cells. Mutant strains having a mutation in genes involved in EPS synthesis were significantly impaired in attachment, whereas strains overproducing this polysaccharide showed higher adhesion efficiency to all of the tested materials. EPS facilitated attachment of bacterial cells to the tested surfaces most probably due to hydrophobic interactions and heterogeneity of the envelope surface. Conclusions EPS produced by R. leguminosarum bv. trifolii plays a significant role in attachment and biofilm formation to both abiotic and biotic surfaces as well as bacterial surface properties.

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