Infiltration characteristics of some clayey soils measured during border irrigation

Infiltration characteristics of soils at five different sites in southeast Australia were estimated using a border infiltrometer method during irrigation. Soil textures at these sites vary from clay loam to clay, with clay content up to 68%. A total of 66 irrigation events were monitored at the various sites. The modified Kostiakov and Horton equations used for describing the soil infiltration characteristics at the time of irrigation, provided a good fit to the field data. The parameter values of the infiltration equations vary with site and with irrigation strip on a given site, depending upon soil texture and water content before irrigation. Large variations in the parameters were also observed from one irrigation to the next on a given strip. The cracking and swelling of the soils during irrigation cycles at most sites had considerable influence on the infiltration characteristics. The initial depth of infiltration, as indicated by the parameter γ in the Horton equation, was found to be inversely related to the soil water content before irrigation. Large values of parameters K_m and γ, respectively, in the modified Kostiakov and Horton equations and small values of b and δ in the same equations for most events indicated that a large proportion of total infiltration occurred in the first few minutes through crack filling and sorption.