A review of approaches to particle-size and microaggregate-size distribution analyses applied in soil science is given. The concepts of the structural organization of soils, primary soil...

This study performs a methodical experiment on adaptation and unification of soil dry sieving analysis. The analysis is based on the Savvinov dry sieving method that uses 0.5-1.5 kg air-dried soil samples which are passed through the 10, 7, 5, 3, 2, 1, 0.5, 0.25 mm sieves. The studied soils are silt loam Eutric Retisol and Haplic Chernozem. From each object, 50 kg of fresh soil was sampled from the plow layer (lm²area). Air-dried soil subsamples of 500 ± 0.5 g were used for analysis, clods bigger than 50 mm were gently crushed by pestle with rubber tip. The sieving parameters were the following: 50 Hz vibration frequency - 3000 rpm (depend on current), from 0.5 to 2.5 mm vibration amplitude and from 0.5 to 5 minutes sieving time. Sieve shaker mechanical work (J) was calculated for each mode. The data approximation was carried out by means of the asymptotic regression function. An optimal dry sieving mode was defined for each soil: Eutric Retisol - 1 mm vibration amplitude during 1 minute, Haplic Chernozem - 2.5 mm vibration amplitude during 2 minutes. In the case of sandy soils dry sieving doesn't require much effort. Therefore, in this experiment only fine macrostructure soils were selected (11-16 % < 2 um clay by laser diffraction method). As a result, the unified dry sieving mode of vibratory sieve shakers was developed which is applicable for all studied soils: 2.5 mm vibration amplitude during 2 minutes and 50 Hz frequency when 500 g air-dried soil sample is used.

Elementary soil particles are the first soil-specific level in the soil structure hierarchy, which is also the object of the soil texture analysis. To disperse soil solids to elementary soil particles (ESP), it is necessary to break the strong bonds between particles by physical action. An effective way of physical dispersion is to treat soil suspensions with ultrasound. However, depending on the type of soil, the required energy level varies, as it is determined by the stability of the soil structure. In this work the experiment with increasing energy (from 65 to 1 101 J·mL^-1) of ultrasonic dispersion at constant power equal to 32.4 W is described. Soil samples from the upper horizons of three types of loamy soils (Retisol, Phaeozem, Chernozem) were used in the experiment. For this purpose, a horn-type ultrasonic disruptor Digital Sonifier S-250D (Branson Ultrasonics, USA) with a stepped solid horn tip (13 mm) was used. It was found that the value of the total energy of dispersion E_t required for complete destruction of soil aggregates to ESP depends on soil type and varies within 200–800 J·mL^-1 for loamy soils with an organic matter content of 1.8–4.6 g. 100 g^-1 soil. For sample preparation of soils for grain-size analysis with a subsequent determination of soil texture class according to Kachinsky classification, the value E_t = 250 J·mL^-1 is sufficient, as it allows obtaining the maximum amount of physical clay (<10 µm) at the minimum duration of sample preparation.