Chinese rose (Rosa chinensis) cultivation in Bohai Bay, China, using an improved drip irrigation method to reclaim heavy coastal saline soils

Abstract

This study investigated whether an improved drip irrigation method for reclaiming heavy coastal saline silt-soils could improve the growth of salt-sensitive plants threatened by soils with high salt contents and poor soil structures in Bohai Bay, China. Chinese rose (Rosa chinensis), an ornamental salt-sensitive plant, was chosen as the experiment material. The improved method used a non-saline root environment during the early stages of salt-leaching, a gravel–sand layer settled below the saline soil but above the water table and optimal soil moisture conditions. To determine the optimal soil moisture conditions, five soil matric potentials (SMPs) at 20cm depth at −5, −10, −15, −20 and −25kPa were studied. The results indicated that the mean soil electrical conductivity of the saturated paste extracts (ECe) and the sodium adsorption ratio (SAR) significantly declined in all five treatments. After three growing seasons, the highest desalinization ratios and SAR reductions reached 89% and 73%, respectively, compared with their initial values and these occurred in the roots of the seedlings exposed to the −5kPa treatment. The mean ECe and SAR values increased linearly as the SMP declined. The plant survival ratio was not affected by the SMP treatment in the first growing season, due to the non-saline root zone, but decreased significantly as the SMP threshold fell in the spring of the second year, and then remained stable in the following season. The highest survival ratio reached 97% for the −5kPa SMP treatment after three growing seasons. Stem diameter and plant height increased during three growing seasons and the largest increases occurred when the SMP was −5kPa in first year, −10kPa in second year and −20kPa in third year. The largest crown diameters were recorded in the −5kPa treatment plots in second year and −20kPa in third year. After three years of reclamation, our results showed that this improved method, which utilized a non-saline root environment during the early stages of salt-leaching, a gravel–sand layer below the saline soil and controlled the SMP threshold of −5kPa in the first year, −10kPa in second year and −20kPa in third year, can be used to reclaim coastal urban saline land for vegetation rehabilitation around Bohai Bay, China.