Effects of Cracking Patterns and Antecedent Soil Water Content on Preferential Flow of Irrigated Water

Abstract

【Objective】 Macropores formed by physical and biological processes provide fast pathways for rainfall and irrigation water to bypass soil matrix. It has important implications not only for hydrological processes but also for biogeochemical processes. In this paper, we investigated the effect of cracking patterns and antecedent soil moisture content on preferential flow of irrigated water. 【Method】 Our study was based on numerical simulation and experiment. We first validated a dual-permeability model against a dye tracing experiment, and then applied it to elucidate how crack patterns, antecedent soil moisture content and irrigation intensity combined to modulate the formation and development of preferential flow of irrigated water in soil. 【Result】 Comparison with experimental results showed that the model is accurate for predicting preferential flow, with R2=0.951 and P<0.01. Shallow small cracks with aperture in the range of 0.2~1.0 cm and in the depth of 0.5~10 cm had little impact on preferential flow, and large cracks with aperture more than 2 cm and expanding to the depth beyond 50 cm were the mechanisms underlying the formation and development of preferential flow. An increase in crack density enhanced both infiltration depth in soil matrix and soil water uniformity. Irrigation intensity less than saturated soil hydraulic conductivity did not trigger preferential flow. Increasing irrigation intensity increased infiltration depth in soil matrix and soil water uniformity in the soil. An increase in antecedent soil water content and cracking density increased water flow in soil matrix and soil water uniformity because of the reduced preferential flow. 【Conclusion】 In the fields with soil shrinkages and rich organic matters, reducing irrigation intensity and irrigating before soil water content drops below a certain level can reduce preferential flow and improve irrigation uniformity consequently.

Keywords

• crack preferential flow
• dual-permeability models
• fracture distribution density
• antecedent water content
• irrigation intensity