Salt Accumulation above Shallow Ground Water Table at Songnen Plain, Heilongjian, China

Abstract

Salt accumulation is one of the most serious threats for plant production in northeast China. Field survey and one-year continuous monitoring on soil physical conditions and water table had been conducted in an experimental station of Northeast Forestry University at Heilongjian, China. Annual rainfall was 356 mm while potential evaporation during summer period of 2006 estimated by Thornsweit method was 540 mm. Soil of the study site was mostly clayey. Salt accumulation on soil surface showed heterogenous feature. Salt accumulated areas and vegetated areas adjoin above the same shallow salty ground water table. During summer, when soil water content was nearly saturated, rise in ground water table in response to rainfall was 7 to 12 times larger than the rain depth. This phenomenon is known as reverse-Wieringermeer effect. A 60% of cation contained by shallow ground water was Na and Ca and Mg dominated rest of 40%. However, more than 90% of cation detected at soil surface in salt accumulated areas and at soil layers deeper than 40cm from the surface in vegetated areas was Na. Dynamic behavior of shallow ground water and changes in carbonates solubility due to rise in soil CO₂ concentration following soil respiration might affect salt accumulation at the experimental site.