Plastic film mulching is an effective agricultural measure to restrain soil water evaporation in the arid and semiarid regions of Western China. Based on the plastic film mulching cultivation, muddy water film hole irrigation is an advanced low-cost and high-efficiency irrigation method, which can improve water conservation, increase soil temperature, crop yield and economic efficiency. Therefore, understanding the distribution and transportation characteristics of water and nitrogen under plastic film mulching with muddy water fertilizer irrigation plays an important role to rationally use muddy water. The purpose of this study was to disclose the effects of the sediment concentration on transport characteristics of soil water and nitrogen under muddy water film fertilizer solution free infiltration. The laboratory soil-box experiments were conducted with muddy water film hole irrigation, using five sediment concentration treatments (0(CK), 3%, 6%, 9% and12%). Ammonium calcium nitrate (5Ca(NO3)2•NH4NO3•10H2O) was selected as the fertilizer to be tested, and it was dissolved in muddy water for film hole irrigation infiltration experiment. The fertilizer solution concentration was 600 mg/L. The cumulative infiltration volume, migration distance of the wetting front, soil moisture content and NO3 --N and NH4 +-N contents in the wetted body were observed. The models about: (i) the relationships between the cumulative infiltration volume per unit film hole area and infiltration duration; (ii) the relationship among the vertical migration distance of the wetting front, sediment concentration and infiltration duration were established. The experimental results showed that the sediment concentration had a significant effect on the transport characteristics of soil water and nitrogen. Cumulative infiltration volume per unit film hole area and infiltration duration conformed to Kostiakov model (R2 > 0.9, P < 0.01). With the increase of sediment concentration in muddy water, the infiltration coefficient K decreased gradually, and the infiltration index remained unchanged. The relationship among vertical migration distance of the wetting front and infiltration reduction rate and infiltration duration was a very significant power function. The influence of sediment concentration on the infiltration reduction rate was mainly realized by the influence of the infiltration decay coefficient. Within the same infiltration time, the larger the sediment concentration of muddy water, the smaller the volume of the wetted body and the area with high moisture content, and the smaller the soil moisture content at the same location in the wetted body. With the increase of sediment concentration in muddy water, vertical migration distance of the wetting front decreased gradually. The sediment concentration had a significant effect on the moisture content distribution in the wetted body. All the isoline of moisture content distribution in the wetted body were nearly in the shape of a quarter ellipse, and moisture content distribution in the wetted body was closely related to the movement of water in the soil, and the isoline of moisture content distribution became denser with the increased of the distance away from the center of the film hole. The contents of NO3 --N and NH4 +-N in wetted soil decreased with the increase of sediment concentration in muddy water. NO3 --N mainly distributed in the range of the wetting radius 10 cm, i.e., soil NO3 --N mainly distributed in shallow soil, which was conducive to the absorption and utilization of crop roots. The horizontal direction of the wetted body and the vertical direction of the film hole decreased with the increased of the distance from the center of the membrane hole, while the NH4 +-N mainly distributed in the range of the wetting radius 5 cm, and the radius of the wetted body 5-10 cm. The content of NH4 +-N decreased with the increase of soil depth. The conclusion of this study could provide a theoretical basis and technical support for further study on the infiltration of muddy water film hole irrigation. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
