WATER-PHYSICAL PROPERTIES OF DRAINED PEAT SOILS IN THE FOREST-STEPPE ZONE OF NORTHERN TRANS-URAL REGION

Abstract

Results are given from long-term (1976–2016) studies on water-physical properties of seasonally frozen peat soils in Northern Trans-Ural region. The studies were conducted on the experimental site of 278 hectares having open drain canals and tile drainage, and located on the alluvial terrace above the floodplain of the Tura River in Tyumen District, Tyumen Region. It has been shown that changes in water-physical properties of soils are of a functional nature and mainly due to the economic soil use and soil surface condition, and differ in a decomposition degree of peat-forming plants (20–45 percent, and more). For 40 years, the peat soil thickness decreased from 1.5 to 0.9–1.0 m, by 1.5 cm annually during the first five years after draining. An 86 percent reduction in the peat soil thickness was due to soil compaction rather than organic matter mineralization. The peat soil bulk density was observed to increase due to the natural process of shrinkage and tilling the underlying mineral soil. The density of the solid soil phase increased slightly for the years of study that has indicated the stability of this index: it increased by 5.4 percent in the 0.3 m layer of medium-textured peat soil for 35 years, and by 1.2 percent in shallow soil for 20 years. It has been shown that the agricultural use of soils impacted the mineralization of peats that resulted in the reduction in the minimum water capacity: by 11.5 percent in the root layer (0.3 m) of medium-textured soil for 35 years; by 6.4 percent in shallow soil, and by 10.2 percent in the peat layer (0.2 m) of peaty-gley soil for 20 years.