Consequences of Textural Analysis Methods on Time Lag Estimates.

Consequences of textural analysis methods on time lag estimates O. Fenton1, T.G. Ibrahim2, P.N.C. Murphy3, S.C. Sherriff1, S.E. Vero1, D. Ó hUallacháin1 1Teagasc, Environment Research Centre, Johnstown Castle, Co. Wexford, Ireland 2Department for Environment, Food and Rural Affairs, London, UK 3School of Agriculture & Food Science, University College Dublin, Co. Dublin, Ireland Pedotransfer functions (PTFs) allow soil properties such as water content and conductivity to be inferred from more easily measurable attributes such as texture and bulk density. However, differences in sand, silt and clay proportions as a result of analysis methods can arise, with consequences for PTF outputs. These differences can in-turn influence the results of numerical models employing said data. A 1 m deep grassland profile, subdivided into a grid (1.4 m by 1.4 m, divided into 49 equal sampling areas), was analysed for texture according to the hand, pipette, hydrometer and laser diffraction methods. The ROSETTA PTF was used to derive hydraulic parameters from these analyses, and incorporated into Hydrus 1D to calculate initial breakthrough (IBT) time lags through the soil profile to groundwater according to each soil texture method. The hand texturing technique (field method) resulted in generic PTF results, which poorly reflected the hydraulic parameters of the soil and produced time lag estimates which were slower (0.07 to 0.19 yrs) than those produced via the three laboratory methods. While the pipette, hydrometer and laser diffraction methods differed in sand, silt and clay apportioning, the consequences on time lag estimates did not exceed 0.04 yrs. These differences are likely to be inconsequential within the context of expected IBT timescales. For this purpose, a laboratory method is therefore preferable to field analysis, but selection of method is of minor importance and may be conducted according to resource availability.