This R function models the soil water balance (SWB) for two soil layers based on relatively simple assumptions. It is a simple method to calculate actual evapotranspiration, downward water flux (leaching), and upward water flux (or capillary rise) from two soil layers and the net flux between the two soil layers. The necessary input data comprises the change in soil water storage between two time steps per soil layer (e.g. from repeated volumetric soil water content measurements), potential evapotranspiration, precipitation, and the percentage of roots in the top soil layer. The soil water balance model is described in detail in Leimer et al. (2014). It is based on a soil water balance model by Kreutziger (2006) and assumes that there is no lateral flow. The model was well validated against the numeric models WAVE and Hydrus 1D, which are based on the Richards equation (Kreutziger 2006, Sprenger et al. 2013). The soil water balance model has been applied in several studies (e.g., Oelmann et al. 2007, Sprenger et al. 2013, Leimer et al. 2018). Usage instructions: The function just needs to be executed in R to be usable. It does not require any special packages. The R script contains more instructions on how to use the function. At the end of the R script, there are two application examples, one for an application with two soil layers and one with only one soil layer. References: Kreutziger (2006). Rückkopplungseffekte verschieden diverser Grünlandökosysteme auf die Komponenten des Bodenwasserhaushalts an einem Auestandort der Saale. Dissertation. Friedrich Schiller University Jena: Jena, Germany Leimer, S., Bischoff, S., Boch, S., Busch, V., Escher, P., Fischer, M., Hänsel, F., Hölzel, N., Kerber, K., Klaus, V., Kleinebecker, T., Michalzik, B., Nauss, T., Schäfer, D., Schöning, I., Schwarz, M. T., Siemens, J., Thieme, L., Wöllauer, S., Wilcke, W. (2018): Does plant diversity affect the water balance of established grassland systems? Ecohydrology 11: e1945. DOI: 10.1002/eco.1945 Leimer, S., Kreutziger Y., Rosenkranz S., Beßler H., Engels C., Hildebrandt A., Oelmann Y., Weisser W.W., Wirth C., Wilcke, W. (2014): Plant diversity effects on the water balance of an experimental grassland. Ecohydrology 7: 1378-1391. DOI: 10.1002/eco.1464 Oelmann, Y., Kreutziger, Y., Temperton, V.M., Buchmann, N., Roscher, C., Schumacher, J., Schulze, E.D., Weisser, W.W., Wilcke, W. (2007). Nitrogen and phosphorus budgets in experimental grasslands of variable diversity. Journal of Environmental Quality 36: 396–407. DOI: 10.2134/jeq2006.0217 Sprenger, M., Oelmann, Y., Weihermueller, L., Wolf, S., Wilcke, W., Potvin, C. (2013). Tree species and diversity effects on soil water seepage in a tropical plantation. Forest Ecology and Management 309: 76-86. DOI: 10.1016/j.foreco.2013.03.022

Two datasets that were calculated with this R function can be found in the Biodiversity Exploratories Information System (http://www.bexis.uni-jena.de/): - "Annual water fluxes (Grassland, VIPs, 2010-2015)" (Dataset id: 22486) - "Annual water fluxes grassland EPs 2010-2016" (Dataset id: 22746)