[Sap flow of Amorpha fruticosa in the secondary saline-alkali land in Ningxia Yellow River irrigation area, China.].

From May to October in 2017, the sap flow, water consumption and the effects of environmental factors on the sap flow of Amorpha fruticosas with different stem diameters under different water and salt conditions were examined with the packaged sap flow measuring system in a secondary saline-alkali land of Ningxia Yellow River irrigation area. The sap flow rate showed a broad peak curve with no obvious phenomenon of 'midday break' in sunny days and a multi-peak curve in cloudy, overcast and rainy days. Weak sap flow was found at night. In the growing season (May - October), total sap flow of A. fruticosas with basal stem diameters of 13, 16 and 22 mm were 138.14, 206.06, 370.11 kg, respectively. The water consumption was largest in June and July, accounting for about 50% of the whole growing season, followed by May and August, and lowest in September and October. At both 0.5 h and day scales, photosynthetically active radiation (PAR) was the dominant meteorological factor affecting the sap flow. In the first growth stage (May 13th - August 19th), soil water in shallow layer (0-40 cm) had significant effect on the sap flow of A. fruticosas with three different diameters, and soil salt in shallow layer had significant inhibitory effect only on A. fruticosa with the diameter of 13 mm. In the second growth stage (August 20th - October 10th), soil water and soil salt had no significant effect on A. fruticosas with three different diameters. In summary, the A. fruticosas with diameters <13 mm was not suitable for planting in saline soil (electrical conductivity (EC)>2 dS·m), and individuals with diameters >16 mm could grow well in saline soil (EC=5 dS·m). Moreover, reasonable irrigation should be carried out in the vigorous growth stage of the A. fruticosas.