Connecting saturated hydraulic conductivity to soil aggregation on croplands along a European climate transect

Abstract

Abstract

Soil aggregates facilitate the infiltration of water into soils. However, information on soil aggregates has not been used for prediction of saturated hydraulic conductivity ( Ks ) in hydrological or Land Surface Models (LSM) so far. We hypothesized that aggregate size, described by the mean weight diameter (MWD), is a key driver of Ks across different climates. To test this, 49 cropland soils were sampled along a climosequence from Northern Sweden to Southern Spain. Tension infiltrometer measurements were performed to determine Ks , which were then predicted using basic soil properties and aggregate size. 10 existing pedotransfer functions (PTFs) using easy-to-measure soil properties were tested. Without recalibration of the regression coefficients to our data, all existing PTFs performed poorly. After calibration, Root Mean Squared Error (RMSE) and R 2 values improved to 0.81–1.10 (ln Ks ) and 0.10–0.51, respectively. Subsequently, two new regression-based PTFs were developed, using soil organic carbon (SOC) content and soil texture as predictors, and explained up to 61% of the data variability. Additionally, MWD could be predicted using soil texture, bulk density, and SOC, with an R 2 of 0.9 and an RMSE of 343 µm, which allowed replacement of laboratory MWD measurements. Aggregate MWD alone could not predict Ks , but the performance of the two newly developed PTF substantially reduced the RMSE and increased the R 2 up to 0.68 after combining MWD with soil texture and SOC. Using simple linear models for predicting aggregate MWD and implementing MWD into PTFs allows for better Ks estimation , and thus, water infiltration and transport in soils.