## 2 Materials and Methods  
### Field Survey  
The field plots are located in the northern part of Fergana Valley (Figure 1), composed of various types of late Pleistocene and current Holocene sediments and parent materials. During the 20 th century, the relief and environment of the Fergana Valley were intensively transformed as a result of land reclamation, soil transfer, soil drainage, and further irrigation and reclamation. However, in the same place one can find places with uncultivated (reference) soils, also used in this research in comparison with the same types of soils, transformed by agricultural impact (surface-irrigated agricultural soil). Uncultivated and irrigated agricultural soils were sampled in the areas indicated in Figure 1. Soil sections were plotted in irrigated and uncultivated plots. Soil samples were collected in triplicate from each genetic soil horizon. After air-drying, the samples were prepared as a mean sample for further analysis.  
The climate is dry, with an average precipitation rate of about 200 mm and average annual temperature of about 14.3 \({}^{\circ}\)C. The valley belongs to a dry subtropical climate. Water deficit makes agriculture completely impossible without irrigation, which completely depends on the supply region with waters of natural sources--rivers and artificial irrigation channels. Currently, more that 95% of the region's area is completely occupied by anthropogenic soils, mainly of agrogenic origin.  
The soils investigated are natural and irrigated Calcisols (Serozems) of the northern Fergana Valley. The \"Calcisols\" are more close term in the WRB soil taxonomy system [13] to \"Serozems\" in USSR (Soviet) soil taxonomy [14]. Serozems are absent in current Russian  
Figure 1: Location of Fergana Valley and sampling sites for each type of soil (Google Earth data).  
classification, because it concerns only the Russian lands, where there are no Serozems. Nevertheless, in our collaboration we use the terminology of current Russian soil taxonomy [15] and its designation of soil horizons. A schematic description of soil profiles and photos of selected soil profiles is provided of Figure 2.  
Agrogenic soils are characterized by the same type of profiles, but the topsoil horizon is changed to an arable version of the P horizon in the Russian soil taxonomy--P [15] which means plughed, tilled, or arable horizon. Thus, if the initial layer was AU, plughed will be PU. Thus, the dark humus horizon became a dark humus arable one. The same applies to the light humus layer AJ, which became a light humus arable horizon. Designated as lithogenic carbonate, inherited from parent materials, they are described as Cea in the parent material in the Russian soil taxonomy [15] and as C\(\alpha\) in WRB [13]. The accumulation of secondary carbonate in the middle part of the solum is a diagnostic feature of Calcisols; they are designated as \"CA\" in capital letters in addition to a designation of soil genetic horizon, e.g., B + CA = BCA. If secondary carbonate is presented by dense noodles, it should be indexed as \"na\". Gleyification is designated by symbol \"g\".  
The soils are formed on parent material of different genesis. They are all carbonate containing and have features of gleyification caused by the presence of ground water at the depths of 80-100 cm. The humus horizon is more pronounced and dark-colored in Dark and Typical Calcisols than in Light Calcisol. In the horizon of the secondary accumulation of carbonates, BCAnc, \"nc\" means accumulation nodules of cemented carbonates. This horizon is more expressed in Dark and Typical Calcisols. Gleyic features are more expressed in Light Calcisols.