Integrated use of saline water and rootzone matric potential control for saline soil reclamation and shrub growth

A four-year field experiment was carried out to evaluate an integrated use of saline water for the saline soil reclamation in Hebei Province of North China. A landscape shrub (Caryopteris × clandonensis ‘Worcester Gold’) was cultivated using drip irrigation scheduled by rootzone soil matric potential control at five levels of water salinity (ECi): 0.8, 3.1, 4.7, 6.3, and 7.8 dS·m−1. Soil matric potential control was applied using a threshold of −5, −10, −15, and −20 kPa in the first, second, third, and fourth year, respectively. After four growing seasons, the saline soil (initial ECe value of 27.8 dS·m−1) was reclaimed to slightly saline soil for 0–1 m depth (4.1–7.2 dS·m−1) under drip irrigation with saline water of ECi < 7.8 dS·m−1. The salt leaching efficiency of root zone soil was highest in the first year and lowered year-by-year. The plants strongly responded to the different soil water and salinity regime. Significant decreases in survival rate, plant growth, and shoot dry weight in response to increasing ECi were found. To achieve a relative survival rate of >50%, the threshold salinity of irrigation water for ‘Worcester Gold’ cultivation was 7.8, 7.0, 5.6, and 5.3 dS·m–1, for the first, second, third, and fourth growing season, respectively. It is recommended to use an inter-seasonal evolving matric potential threshold of −10 kPa for dry season of the third year, −15 kPa for rainy season of the third year and dry season of the fourth year, and −20 kPa for rainy season of the fourth year.