Objective  In forest and fruit irrigation operations, the commonly used water-saving irrigation methods, such as dropper and sprinkler irrigation, are easy to produce evaporation loss and salinization because the water and fertilizer are poured on the surface. It is urgent to effectively and directly irrigate the underground roots of fruit trees and ensure the water and fertilizer not overflow to the surface.

  Method  According to the actual application scenario, the design requirements of the device were analyzed, and an underground self-sealing pressure irrigation device was designed, which can guarantee the pressure self-sealing structure to the surface. Single-factor and multi-factor test on this device was designed. Soil type, water supply pressure and injection depth were selected as the influencing factors, with the target of the injection amount. Origin software was used for single-factor test analysis. Design-Expert software was used for multi-factor test analysis, and a regression model was established. The actual appropriate parameters and the parameters of the influence of injection amount were explored. The reliability of the model was verified by comparing the actual trial with the obtained regression model formula.

  Result  The single-factor test results showed that the injection amount increased with the water supply pressure, and decreased with the water injection depth. In multi-factor test, the regression model was optimized, and the suitable water supply pressure of the common soil was 287 kPa, the suitable water injection depth was30 cm, and the deviation between predicted value and the actual value of the injection amount was less than 5%. The parameter optimization results were reliable.

  Conclusion  The device can meet the initial design requirements, realize the effective direct irrigation of fruit trees underground root, and ensure no overflow to the surface. The reliability of the model can support data for the subsequent device practical application, further development, and the development of underground pressure irrigation technology.