Technical Note: Best of both worlds? Combining undisturbed soil monoliths for indoor runoff experiments

Abstract. A major decision in soil hydrological research is whether to conduct experiments outdoor or indoors. Both approaches have their advantages and trade-offs. Using undisturbed soil monoliths combines some of the advantages of outdoor and indoor experiments, however, there are often size limitations. While push-methods can be used for small- to medium-sized soil blocks, acquiring larger monoliths necessitates heavy machinery. A promising approach is the combination of smaller blocks to a single large monolith, thereby optimizing cost and labour efficiency as well as representativity and upscaling potential. To this end, we compared the runoff properties of medium-sized (1x 0.5 x 0.35 m) grassland soil monoliths cut in half and re-combined with uncut blocks. We conducted artificial runoff experiments and analyzed the outflow from four flow pathways (surface runoff, subsurface interflow, percolating water, laterally exported water) and surface runoff velocity parameters. Our results suggest that the effects of the re-combination procedure are negligible compared to the variation in the data caused by the inherent soil heterogeneity. Further research is needed for a definite conclusion. Nevertheless, we propose that the benefits of combining soil monoliths outweigh the potential disadvantages.