Spatial variability of saturated hydraulic conductivity at the hillslope scale: Understanding the role of land management and erosional effect

In this study, detailed field experiments were conducted at three hillslopes in southeast Iowa with different agricultural management practices, namely Conservation Reserve Program (CRP), no-till, and conventional till, to identify the effects of land use on saturated hydraulic conductivity, Ksat, variability. On average, 40 measurements per field were concomitantly performed using an array of semi-automated double ring infiltrometers (DRIs) to ensure adequate spatial representation of Ksat per hillslope. The semi-automated DRIs allowed for continuous operation up to 200h so that a “true” steady state condition could be reached during the monitoring period. These measurements were complemented with pedon measurements for soil texture, bulk density, and other biogeochemical properties at the same locations. A statistical analysis showed that Ksat exhibited a log-normal distribution and the harmonic mean of the Ksat values proved to be the most representative mean. Two distinct patterns were observed in the developed Ksat spatial distribution maps for the three hillslopes. The map for the CRP hillslope showed a “strip pattern” while the cultivated fields depicted a “mosaic pattern”. The strip pattern at the CRP was attributed to past flow-driven preferential erosion along the main drainage-way, which removed the finer soil fractions and exposed a loam substratum with a relatively higher sand content that yielded higher Ksat values in the drainage-way. The mosaic patterns in the no-till and tilled fields were attributed to the mixing of soil from cultivation during the crop rotations. A correlation analysis between Ksat and different soil properties confirmed the patterns shown in the Ksat maps and further revealed the correspondence of Ksat with key soil properties. Soil texture dominated the infiltration process in soils with a higher sand content (>15%), whereas bulk density dominated the infiltration process in soils experiencing the effects of compaction due to agricultural activity.