Effect of the micro-sprinkler irrigation method with treated effluent on soil physical and chemical properties in sea reclamation land

Abstract

To develop a micro-sprinkler method with treated effluent for tall fescue (Festuca arundinacea) cultivation in sea reclamation land and test its effect on soil physical and chemical properties, a field experiment with five treatments of water quality was conducted in 2015–2016. The five treatments of water quality were created with a mixture of treated effluent (EC, 4.2–6.9 dS/m) and fresh groundwater, and the percentage of treated effluent was 0%, 25%, 50%, 75% and 100%. Saline soil contained a gravel-sand layer imbedded at depth of 60 cm. Irrigation management was divided into three stages, enhanced salt leaching stage (continuous irrigation), water-salt regulation stage (irrigation based on the soil matric potential (SMP) at −5 KPa) and normal irrigation stage (irrigation based on the SMP at −20 KPa). The results indicated that the first stage lasted for 10 days, while the electrical conductivity of saturated extracts (ECe) of the surface 10 cm from 38.29 dS/m dropped to 4.23–6.28 dS/m. After the second stage (3.5 months), the ECe in the 0–60 cm soil layer dropped to 1.42–3.16 dS/m. During these stages, treatment with 50% treated effluent led to relatively good infiltration and lower salinity and was therefore good at enhancing the salt leaching efficiency. In the third stage, the observed ECe of the 0–60 cm changed slightly, but ≤75% treated effluent could maintain the soil salinity below the threshold salinity of tall fescue, even in the rainless season. During the process, soil sodium adsorption ratio decreased, while soil pH increased first and then decreased. Soil available phosphorus content showed a close correlation with treated effluent and the biomass of tall fescue. Moreover, the tall fescue maintained normal growth. Therefore, it is possible to use treated effluent to micro-sprinkler irrigation on tall fescue in sea reclamation land.