Responses of Water and Salt Parameters to Groundwater Levels for Soil Columns Planted with Tamarix chinensis

Groundwater is the main water resource for plant growth and development in the saline soil of the Yellow River Delta in China. To investigate the variabilities and distributions of soil water and salt contents at various groundwater level (G(L)), soil columns with planting Tamarix chinensis Lour were established at six different G(L). The results demonstrated the following: With increasing G(L), the relative soil water content (RWC) declined significantly, whereas the salt content (S-C) and absolute soil solution concentration (C-S) decreased after the initial increase in the different soil profiles. A G(L) of 1.2 m was the turning point for variations in the soil water and salt contents, and it represented the highest G(L) that could maintain the soil surface moist within the soil columns. Both the S-C and C-S reached the maximum levels in these different soil profiles at a G(L) of 1.2 m. With the raise of soil depth, the RWC increased significantly, whereas the S-C increased after an initial decrease. The mean S-C values reached 0.96% in the top soil layer; however, the rates at which the C-S and RWC decreased with the G(L) were significantly reduced. The RWC and S-C presented the greatest variations at the medium (0.9-1.2 m) and shallow water levels (0.6 m) respectively, whereas the C-S presented the greatest variation at the deep water level (1.5-1.8 m). The RWC, S-C and C-S in the soil columns were all closely related to the G(L). However, the correlations among the parameters varied greatly within different soil profiles, and the most accurate predictions of the G(L) were derived from the RWC in the shallow soil layer or the S-C in the top soil layer. A G(L) at 1.5-1.8 m was moderate for planting T. chinensis seedlings under saline groundwater conditions.