Soil salinity management with drip irrigation and its effects on soil hydraulic properties in north China coastal saline soils

A field experiment with five soil matric potential (SMP) treatments (−5, −10, −15, −20 and −25kPa) was used to study the effects of drip irrigation on soil salinity, soil hydraulic properties and vegetation growth in coastal saline soils of north China. Irrigation water came from local groundwater with electrical conductivity of 1.7–2.1dSm−1. The experiment was conducted over three years: 2009–2011. Soil hydraulic properties (hydraulic conductivities, Gardner α and the contribution of pore classes to water flow) were measured three times, i.e. the baseline value (CK) before experiment in 2009, and after one and two years of soil salinity leaching in 2010 and 2011, respectively. Results indicated that low salinity zones existed in the experimental treatments and had expanded during drip irrigation when SMP was controlled at higher than −25kPa, the average electrical conductivity of the saturation paste extract (ECe) in root zones was below 8dSm−1 for −5, −10, −15, −20 and −25kPa treatments, and the highest ratio of desalinization (the removal of salt content accounted for the percentage of initial salt content by leaching) in the whole soil profile for the −5kPa treatment was 64.4%. Meanwhile, the pH of saturated soil extracts concomitantly increased with drip irrigation in the soil profile, whereas it was slightly affected by SMP under drip irrigation. In addition, the hydraulic conductivities, Gardner α and the contribution of macropores (>0.5mm) and mesopores (0.5–0.25mm) to water flow in the surface layer in all five SMP treatments were greater than those in the CK treatment, which indicated that the soil structure had improved. The native vegetation was reed [Phragmites australis (Cav.) Trin. ex Steud.] and suaeda (Suaeda glauca Bge) community. After treatment, the average survival rate of low salt-tolerant plants (Hibiscus syriacus, Prunus cerasifera Ehrh., Ilex buxoides S.Y. Hu and Ligustrum lucidum) was 48.9% at the end of the third year of treatment. Overall, based on salt ratio of desalinization, the SMP above −5kPa at a depth of 20cm immediately under a drip emitter could be used as an indicator of irrigation scheduling for vegetation rehabilitation in north China coastal saline soils.