This data set contains measurements of soil hydraulic properties, i. e. field capacity and permanent wilting point. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plot size was reduced to 5 x 6 m and plots were weeded three times per year.Field capacity and permanent wilting point at 10, 20 and 30 cm depth were derived from soil texture data of 2002 and bulk density 2006 by using pedotransfer functions.Soil texture was determined from undisturbed soil cores at 27 locations distributed throughout the experimental site in spring 2002 before plot establishment. Soil cores were taken to 100 cm depth and separated in depth increments with a resolution of ten cm from ground level to 40 cm depth and 20 cm from 40 cm to 100 cm depth. The bulk material was passed through a sieve with 2 mm mesh size and only fine soil was used for the investigation of soil texture. Grain size fractions according to DIN 19683-2 for every sample were then determined at the laboratory for geoecology of Jena University by a combined sieve and hydrometer analysis. Values for each plot were interpolated by ordinary kriging and the interpolated values were used for the investigation of field capacity and permanent wilting point.Soil bulk density was determined from undisturbed soil samples to a depth of 30 cm. Three soil cores per plot were taken with a split tube sampler with an inner diameter of 4.8 cm and separated in depth increments of five cm. The bulk material was passed through a sieve with 2 mm mesh size, dried to constant weight at 40 °C and subsequently weighed to calculate the density.The determination of field capacity and permanent wilting point was based on pedotransfer functions described in Zacharias and Wessolek (2007). Applied was equation four (where sand content 66.5 %) to derive the parameters of the water retention curve. Bulk density for 10 cm was obtained by taking the average of the measured bulk density of 5-10 cm and 10-15 cm, similarly for 20 cm. For 30 cm, bulk density was assumed to be equal to the one measured at 25-30 cm. Water contents at field capacity and permanent wilting point were obtained using the van Genuchte Eq (e.g. eq 1 in Zacharias and Wessolek), and calculating water contents at -330 cm matric potential (field capacity, 1/3 of atmospheric pressure) and at - 15000 cm.

The main experiment on the field site of the Jena Experiment comprises a split-plot design in which additional treatments (e.g. no weeding allowing for invasion of other species, or application of fertilizer) have been applied to subplots along the outer margin of the plots (see Treatment description in the section "further details"). While in this dataset only data from the core area (mown and weeding of all none-sown species twice a year, no additional treatments) is reported, all potential treatments are listed as the first parameters in the data file to guarantee compatibility with other datasets that include different treatments. There are two types of missing values contained in the dataset. Empty cells represent missing values that result from the design of the experiment when the respective value does not occur and could thus not be measured. For example, in the columns of species-specific biomass cells are left blank, when the species was not sown into the respective plot. Missing values that resulted from methodological problems, sampling errors, or lost samples/data are marked with "-9999".This dataset is part of a collection of measurements of physical and chemical soil properties in the Jena Experiment. Similar data from other experiments (e.g. Main Experiment, Dominance Experiment; see details above), other years, or other methods quantifying related data might be available (https://doi.pangaea.de/10.1594/PANGAEA.885439).