Changes in macro- and micronutrient contents of grasses and forbs following Miscanthus x giganteus feedstock, hydrochar and biochar application to temperate grassland S. Schimmelpfennig*, C. Kammann*, G. Moser*, L. Gr€ unhage* and C. M€ uller*,† *Institute for Experimental Plant Ecology, JLU Giessen, Giessen, Germany, †School of Biology and Environmental Science, University College Dublin, Dublin, Ireland Abstract Biochar and hydrochar application to soil holds prom- ise for climate change mitigation. This study provides first insights into the nutrient concentration and removal of grassland vegetation after addition of vari- ous carbon compounds together with pig slurry. Four treatments: control (no carbon application), feedstock, hydrochar and biochar from Miscanthus x giganteus were applied at a permanent grassland site near Gies- sen, Germany. Changes in plant functional groups, biomass production and nutrition status were moni- tored over 2 years. Total biomass production was not affected by the carbon amendments. However, biochar favoured growth of forbs over grasses, while legume growth was increased by all carbon amendments. The initial nutrient concentrations of the carbon com- pounds were enriched according to their degree of carbonization, potentially providing nutrients to plants. The plant biomass from hydro- and biochar amended plots, added up over 2 years, exhibited higher potassium concentrations compared to biomass from feedstock and control plots. All carbon amend- ments led to lower sodium concentrations in total bio- mass, compared to the control. Uncarbonized feedstock led to increased manganese concentrations in total biomass, while the concentrations of all other heavy metals were not influenced by any carbon amendment, compared to the control. From a plant and animal nutritional point of view, none of the car- bon amendments reduced grassland yield or fodder quality. The study suggests that hydrochar and, even more so, biochar may provide a source of potassium to plants. Keywords: biochar, hydrochar, plant growth, grassland, plant nutrients, nutrient concentration Introduction Carbon amendments such as hydrochar and biochar are currently being studied as an option for climate change mitigation (IPCC, 2007; Woolf et al., 2010), with positive side effects on physico-chemical as well as biological soil properties (Lehmann et al., 2006; Atkinson et al., 2010; Titirici, 2013). Depending on feedstock and process production conditions, biochar was found to improve the nutrient status of the amended soil directly by its nutrient content (Chan and Xu, 2009), direct or indirect pH effects (Hossain et al., 2011; Lehmann et al., 2011), or impacts on soil nutrient cycling due to biochar–fertilizer surface inter- actions (Clough et al., 2013). Two meta-studies on the effect of biochar on plant growth revealed an overall positive influence, with yield increases of 10–12% (Jeffery et al., 2011; Biederman and Harpole, 2013), largely depending on the plant species. In contrast, hydrochar has often proved to be detrimental to plant growth and germination, even generating genotoxic effects, assumedly due to N-limitation or labile carbon fractions attached to the hydrochar as residues from the production process (Gaji c and Koch, 2012; Barg- mann et al., 2013; Busch et al., 2013; Wagner and Kaupenjohann, 2014). Results on the long-term effects of carbon amend- ments on the soil–plant matrix in temperate soils are still scarce (Mukherjee and Lal, 2014). The opportuni- ties for biochar to create soils of high fertility require Correspondence to: S. Schimmelpfennig, Institute for Experi- mental Plant Ecology, JLU Giessen, Heinrich-Buff-Ring 26-32, 35390 Giessen, Germany. E-mail: sonja.schimmelpfennig@bot2.bio.uni-giessen.de Received 22 July 2014; Accepted 15 December 2014 doi: 10.1111/gfs.12158 © 2015 John Wiley & Sons Ltd. Grass and Forage Science 1 Grass and Forage Science The Journal of the British Grassland Society The Official Journal of the European Grassland Federation