## 3 Results and Discussion
In irrigated soils, alanine, asparagic acid, glutamine, cysteine, and histidine prevailed, as well as dicarboxylic amino acids lysine and histidine, which have a weakly alkaline medium isoelectric point and are contained in practically all studied soils. Thus, the irrigation effect on the component composition of amino acids and humification degree, corresponds well with data from other regions [28]. The regime of irrigation also effects Calcisols of the Chirchik-Keles interfluve (Uzbekistan) [29]. The profile distribution of the particle-size fraction as well as the alteration of the granulomatous composition are given in Figure 7. Alteration of soil texture under irrigation is a well-known fact [30]. Colmatage is the process of filling of soil porous media with suspended particles brought by irrigation water. Irrigated soils demonstrate increasing fine silt and clay. At the same time, there is a replacement of sand fractions--fine sand content decreases, and a coarse sand fraction appears. In general, however, the change in particle-size distribution occurs within the gradation of one particle-size distribution class. Thus, irrigation transformation of the soil solid phase is rather slow, which is confirmed by the data of [PERSON] [31]. The soils of the adyr zone are described by [PERSON] as containing more primary or secondary loess material [32]. Nevertheless, our Dark Calcisols do not demonstrate features of high presence of loess-type material even in deepest part of the solum. Increased content of the silt fraction (0.05-0.01 mm) in the superficial layers of both reference and irrigated soils may have resulted from aeolian accumulation, because this fraction is known as maximally labile under wind erosion [33; 34]. Data on available nutrient content in fine earth are provided in Table 2. The bulk and labile forms of potassium and phosphorous demonstrate a gradual decline from toposils to the deeper layers in reference and irrigated soils. It is remarkable that in some parent materials labile forms of nutrients are almost absent. Thus, we can conclude that biogenic nutrients are only in part inherited from parent material and are mostly accumulated in soil due to irrigation and application of fertilizers. Conversely, the content of calcium and magnesium carbonates in soils increases with depth, which indicates the important role of mineralized soil water in the profile distribution of these salts. The prevalence of calcium on magnesium shows the favorable chemical state of the soils. The percentages of carbonates in the soils are comparable with results published by previous researchers for Uzbekistan [34] and are essentially lower than those of the parts of the Fergana Valley that belong to Kyrgyzstan [35]. The content of water-soluble base cations are provided in Figure 8. All the soils demonstrate prevailing calcium in component compositions of salts. Irrigated soil is characterized by an increased concentration of magnesium, but calcium also dominates. Thus, the soil solution composition is favorable for plants in terms of formation of soil structure. The potassium content decreases in irrigated Typical and Light Calcisols, but not in irrigated Dark Calcisols. In general, irrigation does not drastically affect the base cation composition of soil solutions. Nevertheless, it was established that irrigation leads to more pronounced alterations of soil salt composition on the Calcisols adjacent to the Samarkand oasis [36]. Thus, irrigation has regional peculiarities in various regions of Uzbekistan. Figure 7: Particle-size distribution and cumulative curves of different reference and irrigated Calcisols.