WATER REGIME AND WATER BALANCE OF MEADOW-CHESTNUT SOILS UNDER SEPARATED FOREST STANDS IN THE NORTHERN CASPIAN SEA REGION

Abstract

Introduction.Meadow-chestnut soils of micro- and meso-depressions of relief, the profile of which has no easily soluble salts, are the most favorable soils for the cultivation of both forest and agricultural crops. The solonetzic complex of the Northern Caspian region is treeless under natural conditions. The normal state of stands is possible here only with the additional soil water supply.  The goal of the research is to assess modern features of water regime and water balance of meadow-chestnut soils of the Northern Caspian sea region under separated forest stands (on the example of soils of the Dzhanybek research station of the Institute of Forest Science, RAS) and assess their moisture supply. Objects and methods. The objects of the research are the separated forest stands, formed as the result of the decay of forest plantations of the sector of state protective forest belt Chapaevsk–Vladimirovka (est. in 1950) as well as the dish with meadow-chestnut soil and salt solonetz in virgin conditions. The spring and autumn five-meter moisture content of soil cover was studied on the virgin soil and under plants in 2009-2017. In 2015-2017, the groundwater table was monitored every month, and the salinity and the composition of groundwater under the research area were investigated.  Results and discussion. It has been revealed that for the last 10 years, groundwater under separated forest stands were characterized with the chloride-sulfate-calcium-magnesium composition. Its mineralization is on the average 4.3 g/l, which exceeds the values obtained for groundwater under meadow-chestnut soils on virgin soil and it is an unfavorable factor for the growth of trees and shrubs.  Moisture cycle in the soils under separated forest stands is on average 1.5-2 times more intense than in virgin lands and 2-3 times more intense than in solonetz. This is due to the larger intake of winter precipitation moisture under forest plantations due to snow retention and snow runoff, as well as the intensive use of groundwater by plantations. Conclusions. During the growing season, the separated forest stands annually dry up the top 250-350 cm of earth cover to a moisture content corresponding to the wilting point - the moisture content of the capillary rupture.  Only frequent spring soaking of soil profiles can compensate this drying. The deeper layers of soil are all year round in the zone of capillary fringe, so there is no autumn moisture deficit at depths below 300 cm. The water regime of the studied soil retains signs of the desiccate-exudative regime with periodic through wetting. The main source of water supply for trees and shrubs is the groundwater. The moisture of the separated forest stands may now be considered to be a good one. However, due to the intensive use of trees and shrubs of ground waters, their salinity in comparison with virgin soils increases, that worsens the current conditions of forest existence.