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Modified Philips Cumulative Infiltration Equation for Cracked Soils
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Pp. 245-248 in Preferential Flow, Water Movement and Chemical Transport in the Environment, Proc. 2nd Int. Symp. (3-5 January 2001, Honolulu, Hawaii, USA) eds. D. D. Bosch and K. W. King. St. Joseph, Michigan: ASAE 701P0006.(doi:10.13031/2013.2087)
Authors: Remegio B. Confesor Jr. and To Phuc Tuong
Keywords: poultry manure, subsurface drainage, macropores
Previously puddled rice soil cracks upon drying. The bulk of irrigation applied may flow through the cracks, bypassing the soil matrix. For assessing irrigation efficiency, it is important to include this bypass flow in the infiltration equation. The Philip's cumulative infiltration equation (I = St0.5 + k, where, I is the cumulative infiltration (mm), S is the sorptivity (mm d-0.5), k is the steady state infiltration (mm d-1), and t is time in days) could not be applied for cracked soils due to the bypass flow that is affected by gravity. We modified it into I = Io + St0.5 + kt by integrating the original infiltration capacity equation (i = 0.5St - 0.5 + k) and designating Io as the constant of integration as time approaches zero (0). The values (mm) of I0 account for the amount of water that filled the volume of the cracks. Infiltration test data of cracked soils (with cracks developed under fallow; grown with transplanted rice, and wet-seeded rice) were then fitted into this modified equation. The data fitted well in the modified equation with high coefficient of determination (R2 = 0.65 to 0.99 at α = 0.01). Differences in the 1-day cumulative infiltration using the modified equation and the changes in the values of Io could explain the difference in size of the cracks developed under different crop establishment methods.
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