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A field experiment comparing different irrigation frequencies and soil matric potential thresholds on potato evapotranspiration (ET), yield (Y) and water-use efficiency (WUE) was carried out in a loam soil. The experiment included five treatments for soil matric potential: F1 (-15 kPa), F2 (-25 kPa), F3 (-35 kPa), F4 (-45 kPa) and F5 (-55 kPa) and six treatments for irrigation frequency: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days). Results indicate that both soil matric potential and drip irrigation frequency influenced potato ET, Y and WUE. Potato ET increased as irrigation frequency and soil matric potential increased. Comparing soil water potential, the highest ET was 63.4 mm (32.1%) more than the lowest value. Based on irrigation frequency treatments, the highest ET was 36.7 mm (19.2%) more than the lowest value. Potato Y and WUE were also found to increase as irrigation frequency increased. Potato Y increased with an increase in soil water potential then started to decrease. The highest Y and WUE values were achieved with a soil matric potential threshold of -25 kPa and an irrigation frequency of once a day.

A B S T R A C THigh salt content in soil, poor soil structure and fresh water shortage are the restricting factors for construction of ecological landscapes in coastal regions with very heavy saline silt-soil. The aim of this work was to develop a method to reclamate the very heavy coastal saline soil using drip-irrigation with saline water for salt-sensitive plants. A field experiment with five treatments of salinity levels of 0.8, 3.1, 4.7, 6.3 and 7.8 dS/m of irrigation water was imposed in the very heavy saline silt-soil in 2012-2014. The initial soil in experimental plots was tilled and broken, and a gravel-sand layer was created at 120 cm depth. Chinese rose (Rosa chinensis) is very sensitive to salt and was chosen as the representative plant. Soil indexes (electrical conductivity of soil saturated extract (EC e ), pH and sodium adsorption ratio (SAR)), growth characters and dry matter production of rose were determined. The results showed that the level of salinity in water had no significant effect on salt leaching in the 0-120 cm soil profile, and significant effects only occurred in shallow soil layers. EC e and SAR of soil profile decreased with irrigation time, but pH of soil initially increased and then decreased. Rose growth and dry weight decreased with increasing of irrigation water salinity. The values of soil salt tolerance threshold were 2.24 dS/m at emergence and 4.48 dS/m in the growth period after emergence. The emergence rate decreased by 53.30% for each unit of EC e increase in the root zone, and dry weight decreased to zero when EC e exceeded 5.36 dS/m. A regulatory method was scheduled for drip-irrigation of saline water to control the soil matric potential (SMP) under a gravel-sand layer for initially saline soils and was effective in reclamation of very heavy coastal saline soil (silt soil) for sensitive species such as Chinese rose. An SMP higher above À5 kPa at 20 cm depth under the emitter in the first year and À10 kPa in the second year, and 6 mm of irrigation water of salinity up to 4.01 dS/m can be used for rose drip-irrigation scheduling, while also maintaining a 50% survival rate.

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