Effects of different soil water matric potentials on growth traits and yield characteristics of sunflower (Helianthus annuus Linn.) under drip irrigation in a salinized farmland in northern China

Crop irrigation based on controlling the matric potential of soil water at the depth of soil fixation in the root zone is more suitable than deficit irrigation for promoting cultivation in arid agricultural areas. However, it remains challenging to determine how controlled irrigation (CI) quantifies crop the response to water limitation and to establish the appropriate CI thresholds based on soil water matric potential. This study was conducted on sunflower fields in Hetao Irrigation District, a typical arid agricultural area in China where this crop is widely grown. Five CI treatments were applied for different soil water matric potentials (-8, -16, -24, -32, and - 40 kPa) to study the effects of CI on the soil environment and the relationship with crop yield. The following conclusions were drawn: (1) after 2 years of CI treatments, secondary salinization was significantly reduced below the defined criteria for saline soils (4 dS/m), achieving desalination of the entire soil profile; (2) the application of CI as an irrigation strategy in the management of sunflower fields significantly improved physiological traits during the crucial period of sunflower yield formation by increasing plant height while reducing stem thickness; (3) two treatments with the greatest difference in the lower limit of control of soil water matric potential under this irrigation strategy exhibited a yield variance ratio that increased from 0.14% in the first year to 15.37% in the second year; and (4) the treatment that controlled soil water matric potential at -24 kPa obtained the highest yield of all treatments in the test cycle, leading to an increase in seed yield of up to 1266.66 kg/ha in 2022 compared to the previous year.