Irrigation quotas influenced the characteristics of the preferential flow in cotton fields under mulched drip irrigation in Northwest China

Preferential flow is associated with potential issues of poor irrigation water-fertiliser efficiency in a cultivated field. In addition, a preliminary understanding of how irrigation quotas contribute to this prevalent phenomenon is limited. Thus, one blank control group and three different irrigation quotas were set (0, 450, 550 and 650 mm) and the dye tracing image method was applied to investigate the characteristics of the preferential flow in cotton fields under mulched drip irrigation. On the basis of the results, we found significant differences in the preferential flow degree between the four groups (P = 0.02); the mean scores of the dyed area ratio Dc and variation coefficient Cv from the soil stained profile were 29.83%, 45.77%, 37.36%, 39.40% and 0.98, 1.12, 1.28, 1.17 for the total irrigation quota 0, 450, 550 and 650 mm, respectively, indicating an increasing and then decreasing tendency for the non-uniformity as well as variation in the soil water flowing as the irrigation quota being put on. At the same time, the preferential flow ratios showed a similar trend compared with Dc as well as Cv, which were 4.64%, 13.70%, 40.03%, and 23.60% for the irrigation amounts of 0, 450, 550, and 650 mm, respectively. In general, we concluded that the degree of preferential flow with an irrigation quota of 550 mm (local irrigation practice) was highest while no irrigation led to a more uniform flow in the cotton fields with film mulched. The present study goes some way towards supplementing our understanding of preferential flow in agricultural practice.