Characterization of soil preferential flow in the paddy field-ridge transition zone of terrace, Southwest China

Terraced fields represent unique agricultural ecosystems in southwestern China, where soil exhibits preferential flow, potentially leading to the loss of water and fertilizers in rice paddies, thus affecting the structural stability of field ridges. However, the understanding of preferential flow characteristics in paddy and ridge soils across different altitudes remains limited. This study investigates the distribution and development of preferential flow in paddy fields and ridges at low, middle, and high elevations within the Hani terraced paddy fields. The results indicate significant variations in soil moisture infiltration with elevation. Preferential flow was predominantly observed in the shallow layers, particularly in the middle elevation areas, where the stained area ratio (SAR) and stained path number (SPN) reached their peaks. The preferential flow ratio (PFfr) was highest at mid-elevations, with values of 50.97 % for rice fields and 97.33 % for ridges, suggesting a more advanced preferential flow in the latter. Additionally, lateral preferential flow from paddy fields to ridges was significant. Key environmental factors, including soil bulk density, total porosity, and organic matter, were found to correlate with preferential flow indicators. In conclusion, variations in soil properties significantly influence water movement, with mid-elevation regions exhibiting greater soil moisture infiltration. To mitigate water loss and prevent ridge collapse, strategies such as loosening paddy fields and adjusting irrigation and fertilization practices are recommended. These findings contribute to enhanced water dynamics and resource management in both natural and modified ecosystems. • At higher altitudes, the intensity of preferential flow and the spatial heterogeneity of water infiltration become more pronounced. • Preferential flow dyeing exhibits a negative correlation with soil bulk density and clay content. • Preferential flow dyeing shows a positive correlation with total porosity, capillary porosity, and soil water content. • Water flow is homogeneous within the inner paddy field; however, a patchy distribution with significant lateral migration is observed in the ridge transition zone.