Effects of rainfall intensity and antecedent soil water content on soil infiltrability under rainfall conditions using the run off-on-out method

SummarySoil infiltrability, or infiltration capacity, is the rate at which water penetrates into the soil at a rate directly controlled by soil factors alone. The infiltrability is of great importance in understanding and managing hydrological processes, crop water supply, irrigation, and soil erosion. The infiltration dynamics measured with the run off-on-out (ROOO) method follows the changes in infiltrability during the infiltration process under rainfall conditions. In this study, the ROOO method was used to quantitatively measure the soil infiltrability under three rainfall intensities (20, 40 and 60 mm/h) and three antecedent soil moisture contents (2.6%, 10.4% and 19.5%, equivalent to 7.5% (air-dry), 30% and 60% of field capacity, respectively, of a clay loam soil. The soil infiltrability determined by the ROOO method decreased with increase in initial soil water content, due to the lower hydraulic gradient at the wetting front. Surface seal formation due to raindrop impact had a significant influence on soil infiltrability and was related to the soil water content. The faster wetting rate of drier soil under higher rainfall intensities, or when using the double-ring infiltrometer for comparison, caused severe aggregate breakdown to promote surface sealing, and significant decrease in soil infiltrability. Cumulative infiltration increased rapidly at the beginning of the infiltration process and then increased approximately linearly with time as the infiltration rate approached to constant. The rate of increase in cumulative infiltration was less under higher initial soil water contents, especially in the initial rainfall stage. Moreover, lower rainfall intensity resulted in higher infiltration rates and greater cumulative infiltration. The soil infiltrability processes measured with the ROOO method were fitted better by Kostiakov, Horton and Philip infiltration models than those measured by the double-ring infiltrometer method. The ROOO method provided reliable data for the entire infiltration process without the limitations of conventional rainfall simulation during the initial phase or of the drawbacks of the double-ring infiltrometer method. The results will have introductory meanings to further studies along this line.