Numerical simulations of soil water-salt movement considering the dynamics of cotton fine root growth under film-mulched drip irrigation

•A semi-elliptic cylindrical wet bulb was forming along the drip line then diverged to the next irrigation.•Salt accumulation zone was formed at the 40–50 cm soil layers and gradually increased to the next irrigation.•The differential distribution of root length density would lead to different influences on soil water-salt distribution.•HYDRUS-3D that considering the dynamic of root growth can improve the accuracy of soil water-salt simulation.