Method to quantitatively partition the temporal preferential flow and matrix infiltration in forest soil

Abstract Preferential flow is a major part of water infiltration, to partition the rainwater into the runoff generation and soil recharge in forest soil. A method is advanced in this study to measure soil matrix infiltration to verify its uniformity, before it was used to partition temporal preferential flow from the total infiltration employing two double-ring infiltrometers. A thin layer of fine sands were placed onto the nylon cloth in the inner ring and between the inner and outer rings of one double-ring infiltrometer to shelter the preferential paths and ensure that water infiltrates the soil matrix only. The other double-ring infiltrometer was directly inserted a shallow depth into soil to measure total infiltration at a nearby spot. Therefore, the difference of the total and the matrix infiltration is used to determine the preferential flow infiltration. Field experiments were conducted at five sites of a forested field in Tianshui Soil and Water Conservation Experimental Station, on the Loess Plateau, Gansu province of China. Experimental results indicated that the soil matrix infiltration processes at the five sites were roughly the same, thereby indicating that the matrix infiltration at one spot could be replaced by that of the nearby spot at the experimental site. The measured matrix infiltration can be used to partition the preferential infiltration from the total. The measured initial preferential flow infiltration rate (PIR) was 2.6–10.2 times of soil matrix infiltration rate (MIR) and the steady PIR was 2.3–4.9 times of that of the MIR. Preferential cumulative infiltration contributed 66–82% to total infiltration. These highlighted that preferential flow was a main part of forest soil infiltration at the experiment sites. This study provides a convenient method for fast determination of preferential flow infiltration in field conditions which is helpful for managing agricultural water resources and infiltration-related ecosystem service.