Background Contour ridging is an effectively agricultural practice applied worldwide that is conducted approximately perpendicular to the overland flow path on sloped land. In practices, the ridges are much too hard to precisely follow the contour of the ground on slopes, and thus results in the formation of low areas in furrows. Thus, rainwater from side slopes or irrigation water easily accumulates in these furrow areas, and then induces the occurrence of ponding infiltration. The ponding infiltration characteristic in contour ridge system differs that on traditional slope, such as flat tillage, downslope tillage. However, little attention has been paid to the ponding infiltration characteristic in contour ridge system.

Methods Based on the ponding characteristic of water in contour ridge system, this study analyzed the temporal variation of infiltration rate and the advancement of wetting front for layered brown soil under five ponding depths, 2, 4, 6, 8 and 12 cm using the suppling water experiment (Mahalanobis) on soil column. Meanwhile, the layer brown soil was respectively packed with bulk density of 1.30 g/cm³ and 1.50 g/cm³ to simulate the infiltration process for plough layer and plow pan. Then, the ponding infiltration process was stimulated with the improved Green-Ampt model.

Results 1) The ponding infiltration process was divided into three phase: Plough layer phase, transition phase, and plow pan phase. During the plough layer phase, infiltration rate sharply decreased and then kept a stable state. However, during the transition phase, infiltration rate firstly changed slightly for a period of time until gradually decreasing. In addition, infiltration rate was closed to a constant during the plow pan phase. 2) The increase of ponding depth enhanced the advancement of wetting front, but slightly changed the advanced process of wetting front. 3) The relationship between infiltration parameter (the initial, average and stable infiltration rate, as well as cumulative infiltration) and ponding depth was fitted to the power function. Compared to ponding depth 2 cm, the average infiltration rate under ponding depth 12, 8, 6 and 4 cm increased by 120.5%, 65.4%, 39.4% and 29.9%, respectively. The linear relationship between infiltration rate and the inverse of wetting front depth at different ponding depths was used to calculate soil saturated hydraulic conductivity (K_s(h)) and the suction at the wetting front. Based on the positively linear correlation between soil saturated hydraulic conductivity and ponding depth (K_s(h)=0.092h+0.76), combined the determination of suction at the wetting front (25.61 cm), the improved Green-Ampt model was established to simulate the ponding infiltration process.

Conclusions The increase of ponding depth enhanced the infiltration capacity, while the increase influence was related to the range of ponding depth. The improved Green-Ampt model could simulate the infiltration process for varied ponding depths. These findings can supply scientific guidance for water use efficiency and water resources regulation in contour ridge system.