Floodplain Soils of the Closed Uldz–Torei Basin (Mongolia).

Data on the diversity; morphological structure; and physical, chemical, and agrochemical properties of soils within the Uldz River floodplain (Mongolia, Uldz–Torei plain) have been obtained for the first time. The predominance of alluvial medium-thick dark humus soil type of saline and quasi-gleic subtypes is established. A very important feature in soil genesis is identified, namely, a high level of groundwater and light texture of alluvial deposits, determining the same type of plant residues transformation (dark humus accumulations). It is concluded that the differences between soils are due to the degree of salinity and the type of chemistry. The alluvial soils under study are alkaline and slightly saline, predominantly of chloride and soda-chloride type of salinity for anions and of magnesium–sodium or sodium–magnesium type for cations. Solonchaks that form in the lower parts of the floodplain have different types of salinity within genetic horizons for anions and a sodium type of salinity for cations. Phytocenoses grown on these soils are of low productivity, projective cover, and depleted species composition and are represented only by halophytes. Unfavorable factors for plant growth are responsible for the occurrence of light humus processes, similar to the zonal soil. The level of natural fertility of the soils under study is found to be very low because of their thin layered profile; unfavorable physical, chemical, and agrochemical properties; and especially low content of nitrate nitrogen and labile phosphorus. Destructive agrogenic processes are described that are possible when alluvial dark humus soils are involved in arable use. These soils should be mainly used as grasslands and hay pastures, and it is recommended that "focal" plots should be allocated for arable land in compliance with soil conservation measures. To increase the biopoductivity of the floodplain lands, it is necessary to use various types of manure, composts, green manure, and mineral fertilizers (primarily nitrogen and phosphorus). Typical solonchaks have unfavorable physical, chemical, and meliorative properties and an extremely low level of natural fertility. In this regard, they should be classified as marginal or virtually unsuitable for use in agricultural production with the occasional grazing of farm animals. [ABSTRACT FROM AUTHOR]