Management of sea reclamation land using drip irrigation with treated effluent and its effect on Rosa chinensis

The field experiment was conducted to develop a drip irrigation management method using treated wastewater effluent for Chinese rose (Rosa chinensis) cultivation in coastal saline soil during 2015–2016. Five irrigation treatments were evaluated consisting of treated effluent (electrical conductivity, 4.2–6.9 dS/m) blended with fresh water (effluent proportions of 0%, 25%, 50%, 75% and 100%). Chinese rose was planted in ridges above a gravel-sand layer at the depth of 100 cm. Irrigation was based on soil matric potential (SMP) and managed in three stages, including enhanced salt leaching stage (continuous irrigation), water-salt regulation stage (SMP, −5 kPa) and normal irrigation stage (SMP, −10 kPa). The study showed drip irrigation with different proportions of treated effluent could enhance salt leaching. After the first two stages (about 3.5 months), soil salinity above the gravel-sand layer was reduced from 37.4 dS/m to 2.16–3.86 dS/m. Throughout one year of the normal irrigation stage, salinity increases that exceeded 1 dS/m in the root-zone soil were observed in the treatments of 75% and 100% treated effluent, and mainly during a dry season. In Bohai region, the survival rate of Chinese rose decreased by 0–5% in the first two stages of irrigation, depending on treatments, but a notable reduction in plant survival rate was found in the first month of a new growing period under normal irrigation. Therefore, in saline soil typical of sea reclamation land, drip irrigation with different levels of treated effluent can be used for Chinese rose cultivation in the enhanced salt leaching and water-salt regulation stages of irrigation. Irrigation water containing ≤50% treated effluent is feasible in the normal irrigation stage, except for the first month of the new growing period, for which water containing 25% treated effluent should be used.